1 /*
   2  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.  Oracle designates this
   7  * particular file as subject to the "Classpath" exception as provided
   8  * by Oracle in the LICENSE file that accompanied this code.
   9  *
  10  * This code is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13  * version 2 for more details (a copy is included in the LICENSE file that
  14  * accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License version
  17  * 2 along with this work; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19  *
  20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  */
  24 
  25 /* pngrtran.c - transforms the data in a row for PNG readers
  26  *
  27  * This file is available under and governed by the GNU General Public
  28  * License version 2 only, as published by the Free Software Foundation.
  29  * However, the following notice accompanied the original version of this
  30  * file and, per its terms, should not be removed:
  31  *
  32  * Last changed in libpng 1.6.22 [May 26, 2016]
  33  * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
  34  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  35  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  36  *
  37  * This code is released under the libpng license.
  38  * For conditions of distribution and use, see the disclaimer
  39  * and license in png.h
  40  *
  41  * This file contains functions optionally called by an application
  42  * in order to tell libpng how to handle data when reading a PNG.
  43  * Transformations that are used in both reading and writing are
  44  * in pngtrans.c.
  45  */
  46 
  47 #include "pngpriv.h"
  48 
  49 #ifdef PNG_READ_SUPPORTED
  50 
  51 /* Set the action on getting a CRC error for an ancillary or critical chunk. */
  52 void PNGAPI
  53 png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)
  54 {
  55    png_debug(1, "in png_set_crc_action");
  56 
  57    if (png_ptr == NULL)
  58       return;
  59 
  60    /* Tell libpng how we react to CRC errors in critical chunks */
  61    switch (crit_action)
  62    {
  63       case PNG_CRC_NO_CHANGE:                        /* Leave setting as is */
  64          break;
  65 
  66       case PNG_CRC_WARN_USE:                               /* Warn/use data */
  67          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
  68          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
  69          break;
  70 
  71       case PNG_CRC_QUIET_USE:                             /* Quiet/use data */
  72          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
  73          png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
  74                            PNG_FLAG_CRC_CRITICAL_IGNORE;
  75          break;
  76 
  77       case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
  78          png_warning(png_ptr,
  79             "Can't discard critical data on CRC error");
  80       case PNG_CRC_ERROR_QUIT:                                /* Error/quit */
  81 
  82       case PNG_CRC_DEFAULT:
  83       default:
  84          png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
  85          break;
  86    }
  87 
  88    /* Tell libpng how we react to CRC errors in ancillary chunks */
  89    switch (ancil_action)
  90    {
  91       case PNG_CRC_NO_CHANGE:                       /* Leave setting as is */
  92          break;
  93 
  94       case PNG_CRC_WARN_USE:                              /* Warn/use data */
  95          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
  96          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
  97          break;
  98 
  99       case PNG_CRC_QUIET_USE:                            /* Quiet/use data */
 100          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
 101          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
 102                            PNG_FLAG_CRC_ANCILLARY_NOWARN;
 103          break;
 104 
 105       case PNG_CRC_ERROR_QUIT:                               /* Error/quit */
 106          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
 107          png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
 108          break;
 109 
 110       case PNG_CRC_WARN_DISCARD:                      /* Warn/discard data */
 111 
 112       case PNG_CRC_DEFAULT:
 113       default:
 114          png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
 115          break;
 116    }
 117 }
 118 
 119 #ifdef PNG_READ_TRANSFORMS_SUPPORTED
 120 /* Is it OK to set a transformation now?  Only if png_start_read_image or
 121  * png_read_update_info have not been called.  It is not necessary for the IHDR
 122  * to have been read in all cases; the need_IHDR parameter allows for this
 123  * check too.
 124  */
 125 static int
 126 png_rtran_ok(png_structrp png_ptr, int need_IHDR)
 127 {
 128    if (png_ptr != NULL)
 129    {
 130       if ((png_ptr->flags & PNG_FLAG_ROW_INIT) != 0)
 131          png_app_error(png_ptr,
 132             "invalid after png_start_read_image or png_read_update_info");
 133 
 134       else if (need_IHDR && (png_ptr->mode & PNG_HAVE_IHDR) == 0)
 135          png_app_error(png_ptr, "invalid before the PNG header has been read");
 136 
 137       else
 138       {
 139          /* Turn on failure to initialize correctly for all transforms. */
 140          png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;
 141 
 142          return 1; /* Ok */
 143       }
 144    }
 145 
 146    return 0; /* no png_error possible! */
 147 }
 148 #endif
 149 
 150 #ifdef PNG_READ_BACKGROUND_SUPPORTED
 151 /* Handle alpha and tRNS via a background color */
 152 void PNGFAPI
 153 png_set_background_fixed(png_structrp png_ptr,
 154     png_const_color_16p background_color, int background_gamma_code,
 155     int need_expand, png_fixed_point background_gamma)
 156 {
 157    png_debug(1, "in png_set_background_fixed");
 158 
 159    if (png_rtran_ok(png_ptr, 0) == 0 || background_color == NULL)
 160       return;
 161 
 162    if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
 163    {
 164       png_warning(png_ptr, "Application must supply a known background gamma");
 165       return;
 166    }
 167 
 168    png_ptr->transformations |= PNG_COMPOSE | PNG_STRIP_ALPHA;
 169    png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
 170    png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
 171 
 172    png_ptr->background = *background_color;
 173    png_ptr->background_gamma = background_gamma;
 174    png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
 175    if (need_expand != 0)
 176       png_ptr->transformations |= PNG_BACKGROUND_EXPAND;
 177    else
 178       png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
 179 }
 180 
 181 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 182 void PNGAPI
 183 png_set_background(png_structrp png_ptr,
 184     png_const_color_16p background_color, int background_gamma_code,
 185     int need_expand, double background_gamma)
 186 {
 187    png_set_background_fixed(png_ptr, background_color, background_gamma_code,
 188       need_expand, png_fixed(png_ptr, background_gamma, "png_set_background"));
 189 }
 190 #  endif /* FLOATING_POINT */
 191 #endif /* READ_BACKGROUND */
 192 
 193 /* Scale 16-bit depth files to 8-bit depth.  If both of these are set then the
 194  * one that pngrtran does first (scale) happens.  This is necessary to allow the
 195  * TRANSFORM and API behavior to be somewhat consistent, and it's simpler.
 196  */
 197 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
 198 void PNGAPI
 199 png_set_scale_16(png_structrp png_ptr)
 200 {
 201    png_debug(1, "in png_set_scale_16");
 202 
 203    if (png_rtran_ok(png_ptr, 0) == 0)
 204       return;
 205 
 206    png_ptr->transformations |= PNG_SCALE_16_TO_8;
 207 }
 208 #endif
 209 
 210 #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
 211 /* Chop 16-bit depth files to 8-bit depth */
 212 void PNGAPI
 213 png_set_strip_16(png_structrp png_ptr)
 214 {
 215    png_debug(1, "in png_set_strip_16");
 216 
 217    if (png_rtran_ok(png_ptr, 0) == 0)
 218       return;
 219 
 220    png_ptr->transformations |= PNG_16_TO_8;
 221 }
 222 #endif
 223 
 224 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
 225 void PNGAPI
 226 png_set_strip_alpha(png_structrp png_ptr)
 227 {
 228    png_debug(1, "in png_set_strip_alpha");
 229 
 230    if (png_rtran_ok(png_ptr, 0) == 0)
 231       return;
 232 
 233    png_ptr->transformations |= PNG_STRIP_ALPHA;
 234 }
 235 #endif
 236 
 237 #if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
 238 static png_fixed_point
 239 translate_gamma_flags(png_structrp png_ptr, png_fixed_point output_gamma,
 240    int is_screen)
 241 {
 242    /* Check for flag values.  The main reason for having the old Mac value as a
 243     * flag is that it is pretty near impossible to work out what the correct
 244     * value is from Apple documentation - a working Mac system is needed to
 245     * discover the value!
 246     */
 247    if (output_gamma == PNG_DEFAULT_sRGB ||
 248       output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
 249    {
 250       /* If there is no sRGB support this just sets the gamma to the standard
 251        * sRGB value.  (This is a side effect of using this function!)
 252        */
 253 #     ifdef PNG_READ_sRGB_SUPPORTED
 254          png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
 255 #     else
 256          PNG_UNUSED(png_ptr)
 257 #     endif
 258       if (is_screen != 0)
 259          output_gamma = PNG_GAMMA_sRGB;
 260       else
 261          output_gamma = PNG_GAMMA_sRGB_INVERSE;
 262    }
 263 
 264    else if (output_gamma == PNG_GAMMA_MAC_18 ||
 265       output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
 266    {
 267       if (is_screen != 0)
 268          output_gamma = PNG_GAMMA_MAC_OLD;
 269       else
 270          output_gamma = PNG_GAMMA_MAC_INVERSE;
 271    }
 272 
 273    return output_gamma;
 274 }
 275 
 276 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 277 static png_fixed_point
 278 convert_gamma_value(png_structrp png_ptr, double output_gamma)
 279 {
 280    /* The following silently ignores cases where fixed point (times 100,000)
 281     * gamma values are passed to the floating point API.  This is safe and it
 282     * means the fixed point constants work just fine with the floating point
 283     * API.  The alternative would just lead to undetected errors and spurious
 284     * bug reports.  Negative values fail inside the _fixed API unless they
 285     * correspond to the flag values.
 286     */
 287    if (output_gamma > 0 && output_gamma < 128)
 288       output_gamma *= PNG_FP_1;
 289 
 290    /* This preserves -1 and -2 exactly: */
 291    output_gamma = floor(output_gamma + .5);
 292 
 293    if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
 294       png_fixed_error(png_ptr, "gamma value");
 295 
 296    return (png_fixed_point)output_gamma;
 297 }
 298 #  endif
 299 #endif /* READ_ALPHA_MODE || READ_GAMMA */
 300 
 301 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
 302 void PNGFAPI
 303 png_set_alpha_mode_fixed(png_structrp png_ptr, int mode,
 304    png_fixed_point output_gamma)
 305 {
 306    int compose = 0;
 307    png_fixed_point file_gamma;
 308 
 309    png_debug(1, "in png_set_alpha_mode");
 310 
 311    if (png_rtran_ok(png_ptr, 0) == 0)
 312       return;
 313 
 314    output_gamma = translate_gamma_flags(png_ptr, output_gamma, 1/*screen*/);
 315 
 316    /* Validate the value to ensure it is in a reasonable range. The value
 317     * is expected to be 1 or greater, but this range test allows for some
 318     * viewing correction values.  The intent is to weed out users of this API
 319     * who use the inverse of the gamma value accidentally!  Since some of these
 320     * values are reasonable this may have to be changed:
 321     *
 322     * 1.6.x: changed from 0.07..3 to 0.01..100 (to accomodate the optimal 16-bit
 323     * gamma of 36, and its reciprocal.)
 324     */
 325    if (output_gamma < 1000 || output_gamma > 10000000)
 326       png_error(png_ptr, "output gamma out of expected range");
 327 
 328    /* The default file gamma is the inverse of the output gamma; the output
 329     * gamma may be changed below so get the file value first:
 330     */
 331    file_gamma = png_reciprocal(output_gamma);
 332 
 333    /* There are really 8 possibilities here, composed of any combination
 334     * of:
 335     *
 336     *    premultiply the color channels
 337     *    do not encode non-opaque pixels
 338     *    encode the alpha as well as the color channels
 339     *
 340     * The differences disappear if the input/output ('screen') gamma is 1.0,
 341     * because then the encoding is a no-op and there is only the choice of
 342     * premultiplying the color channels or not.
 343     *
 344     * png_set_alpha_mode and png_set_background interact because both use
 345     * png_compose to do the work.  Calling both is only useful when
 346     * png_set_alpha_mode is used to set the default mode - PNG_ALPHA_PNG - along
 347     * with a default gamma value.  Otherwise PNG_COMPOSE must not be set.
 348     */
 349    switch (mode)
 350    {
 351       case PNG_ALPHA_PNG:        /* default: png standard */
 352          /* No compose, but it may be set by png_set_background! */
 353          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
 354          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
 355          break;
 356 
 357       case PNG_ALPHA_ASSOCIATED: /* color channels premultiplied */
 358          compose = 1;
 359          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
 360          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
 361          /* The output is linear: */
 362          output_gamma = PNG_FP_1;
 363          break;
 364 
 365       case PNG_ALPHA_OPTIMIZED:  /* associated, non-opaque pixels linear */
 366          compose = 1;
 367          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
 368          png_ptr->flags |= PNG_FLAG_OPTIMIZE_ALPHA;
 369          /* output_gamma records the encoding of opaque pixels! */
 370          break;
 371 
 372       case PNG_ALPHA_BROKEN:     /* associated, non-linear, alpha encoded */
 373          compose = 1;
 374          png_ptr->transformations |= PNG_ENCODE_ALPHA;
 375          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
 376          break;
 377 
 378       default:
 379          png_error(png_ptr, "invalid alpha mode");
 380    }
 381 
 382    /* Only set the default gamma if the file gamma has not been set (this has
 383     * the side effect that the gamma in a second call to png_set_alpha_mode will
 384     * be ignored.)
 385     */
 386    if (png_ptr->colorspace.gamma == 0)
 387    {
 388       png_ptr->colorspace.gamma = file_gamma;
 389       png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
 390    }
 391 
 392    /* But always set the output gamma: */
 393    png_ptr->screen_gamma = output_gamma;
 394 
 395    /* Finally, if pre-multiplying, set the background fields to achieve the
 396     * desired result.
 397     */
 398    if (compose != 0)
 399    {
 400       /* And obtain alpha pre-multiplication by composing on black: */
 401       memset(&png_ptr->background, 0, (sizeof png_ptr->background));
 402       png_ptr->background_gamma = png_ptr->colorspace.gamma; /* just in case */
 403       png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_FILE;
 404       png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
 405 
 406       if ((png_ptr->transformations & PNG_COMPOSE) != 0)
 407          png_error(png_ptr,
 408             "conflicting calls to set alpha mode and background");
 409 
 410       png_ptr->transformations |= PNG_COMPOSE;
 411    }
 412 }
 413 
 414 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 415 void PNGAPI
 416 png_set_alpha_mode(png_structrp png_ptr, int mode, double output_gamma)
 417 {
 418    png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
 419       output_gamma));
 420 }
 421 #  endif
 422 #endif
 423 
 424 #ifdef PNG_READ_QUANTIZE_SUPPORTED
 425 /* Dither file to 8-bit.  Supply a palette, the current number
 426  * of elements in the palette, the maximum number of elements
 427  * allowed, and a histogram if possible.  If the current number
 428  * of colors is greater than the maximum number, the palette will be
 429  * modified to fit in the maximum number.  "full_quantize" indicates
 430  * whether we need a quantizing cube set up for RGB images, or if we
 431  * simply are reducing the number of colors in a paletted image.
 432  */
 433 
 434 typedef struct png_dsort_struct
 435 {
 436    struct png_dsort_struct * next;
 437    png_byte left;
 438    png_byte right;
 439 } png_dsort;
 440 typedef png_dsort *   png_dsortp;
 441 typedef png_dsort * * png_dsortpp;
 442 
 443 void PNGAPI
 444 png_set_quantize(png_structrp png_ptr, png_colorp palette,
 445     int num_palette, int maximum_colors, png_const_uint_16p histogram,
 446     int full_quantize)
 447 {
 448    png_debug(1, "in png_set_quantize");
 449 
 450    if (png_rtran_ok(png_ptr, 0) == 0)
 451       return;
 452 
 453    png_ptr->transformations |= PNG_QUANTIZE;
 454 
 455    if (full_quantize == 0)
 456    {
 457       int i;
 458 
 459       png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
 460           (png_uint_32)(num_palette * (sizeof (png_byte))));
 461       for (i = 0; i < num_palette; i++)
 462          png_ptr->quantize_index[i] = (png_byte)i;
 463    }
 464 
 465    if (num_palette > maximum_colors)
 466    {
 467       if (histogram != NULL)
 468       {
 469          /* This is easy enough, just throw out the least used colors.
 470           * Perhaps not the best solution, but good enough.
 471           */
 472 
 473          int i;
 474 
 475          /* Initialize an array to sort colors */
 476          png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
 477              (png_uint_32)(num_palette * (sizeof (png_byte))));
 478 
 479          /* Initialize the quantize_sort array */
 480          for (i = 0; i < num_palette; i++)
 481             png_ptr->quantize_sort[i] = (png_byte)i;
 482 
 483          /* Find the least used palette entries by starting a
 484           * bubble sort, and running it until we have sorted
 485           * out enough colors.  Note that we don't care about
 486           * sorting all the colors, just finding which are
 487           * least used.
 488           */
 489 
 490          for (i = num_palette - 1; i >= maximum_colors; i--)
 491          {
 492             int done; /* To stop early if the list is pre-sorted */
 493             int j;
 494 
 495             done = 1;
 496             for (j = 0; j < i; j++)
 497             {
 498                if (histogram[png_ptr->quantize_sort[j]]
 499                    < histogram[png_ptr->quantize_sort[j + 1]])
 500                {
 501                   png_byte t;
 502 
 503                   t = png_ptr->quantize_sort[j];
 504                   png_ptr->quantize_sort[j] = png_ptr->quantize_sort[j + 1];
 505                   png_ptr->quantize_sort[j + 1] = t;
 506                   done = 0;
 507                }
 508             }
 509 
 510             if (done != 0)
 511                break;
 512          }
 513 
 514          /* Swap the palette around, and set up a table, if necessary */
 515          if (full_quantize != 0)
 516          {
 517             int j = num_palette;
 518 
 519             /* Put all the useful colors within the max, but don't
 520              * move the others.
 521              */
 522             for (i = 0; i < maximum_colors; i++)
 523             {
 524                if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
 525                {
 526                   do
 527                      j--;
 528                   while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
 529 
 530                   palette[i] = palette[j];
 531                }
 532             }
 533          }
 534          else
 535          {
 536             int j = num_palette;
 537 
 538             /* Move all the used colors inside the max limit, and
 539              * develop a translation table.
 540              */
 541             for (i = 0; i < maximum_colors; i++)
 542             {
 543                /* Only move the colors we need to */
 544                if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
 545                {
 546                   png_color tmp_color;
 547 
 548                   do
 549                      j--;
 550                   while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
 551 
 552                   tmp_color = palette[j];
 553                   palette[j] = palette[i];
 554                   palette[i] = tmp_color;
 555                   /* Indicate where the color went */
 556                   png_ptr->quantize_index[j] = (png_byte)i;
 557                   png_ptr->quantize_index[i] = (png_byte)j;
 558                }
 559             }
 560 
 561             /* Find closest color for those colors we are not using */
 562             for (i = 0; i < num_palette; i++)
 563             {
 564                if ((int)png_ptr->quantize_index[i] >= maximum_colors)
 565                {
 566                   int min_d, k, min_k, d_index;
 567 
 568                   /* Find the closest color to one we threw out */
 569                   d_index = png_ptr->quantize_index[i];
 570                   min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
 571                   for (k = 1, min_k = 0; k < maximum_colors; k++)
 572                   {
 573                      int d;
 574 
 575                      d = PNG_COLOR_DIST(palette[d_index], palette[k]);
 576 
 577                      if (d < min_d)
 578                      {
 579                         min_d = d;
 580                         min_k = k;
 581                      }
 582                   }
 583                   /* Point to closest color */
 584                   png_ptr->quantize_index[i] = (png_byte)min_k;
 585                }
 586             }
 587          }
 588          png_free(png_ptr, png_ptr->quantize_sort);
 589          png_ptr->quantize_sort = NULL;
 590       }
 591       else
 592       {
 593          /* This is much harder to do simply (and quickly).  Perhaps
 594           * we need to go through a median cut routine, but those
 595           * don't always behave themselves with only a few colors
 596           * as input.  So we will just find the closest two colors,
 597           * and throw out one of them (chosen somewhat randomly).
 598           * [We don't understand this at all, so if someone wants to
 599           *  work on improving it, be our guest - AED, GRP]
 600           */
 601          int i;
 602          int max_d;
 603          int num_new_palette;
 604          png_dsortp t;
 605          png_dsortpp hash;
 606 
 607          t = NULL;
 608 
 609          /* Initialize palette index arrays */
 610          png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
 611              (png_uint_32)(num_palette * (sizeof (png_byte))));
 612          png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
 613              (png_uint_32)(num_palette * (sizeof (png_byte))));
 614 
 615          /* Initialize the sort array */
 616          for (i = 0; i < num_palette; i++)
 617          {
 618             png_ptr->index_to_palette[i] = (png_byte)i;
 619             png_ptr->palette_to_index[i] = (png_byte)i;
 620          }
 621 
 622          hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(769 *
 623              (sizeof (png_dsortp))));
 624 
 625          num_new_palette = num_palette;
 626 
 627          /* Initial wild guess at how far apart the farthest pixel
 628           * pair we will be eliminating will be.  Larger
 629           * numbers mean more areas will be allocated, Smaller
 630           * numbers run the risk of not saving enough data, and
 631           * having to do this all over again.
 632           *
 633           * I have not done extensive checking on this number.
 634           */
 635          max_d = 96;
 636 
 637          while (num_new_palette > maximum_colors)
 638          {
 639             for (i = 0; i < num_new_palette - 1; i++)
 640             {
 641                int j;
 642 
 643                for (j = i + 1; j < num_new_palette; j++)
 644                {
 645                   int d;
 646 
 647                   d = PNG_COLOR_DIST(palette[i], palette[j]);
 648 
 649                   if (d <= max_d)
 650                   {
 651 
 652                      t = (png_dsortp)png_malloc_warn(png_ptr,
 653                          (png_uint_32)(sizeof (png_dsort)));
 654 
 655                      if (t == NULL)
 656                          break;
 657 
 658                      t->next = hash[d];
 659                      t->left = (png_byte)i;
 660                      t->right = (png_byte)j;
 661                      hash[d] = t;
 662                   }
 663                }
 664                if (t == NULL)
 665                   break;
 666             }
 667 
 668             if (t != NULL)
 669             for (i = 0; i <= max_d; i++)
 670             {
 671                if (hash[i] != NULL)
 672                {
 673                   png_dsortp p;
 674 
 675                   for (p = hash[i]; p; p = p->next)
 676                   {
 677                      if ((int)png_ptr->index_to_palette[p->left]
 678                          < num_new_palette &&
 679                          (int)png_ptr->index_to_palette[p->right]
 680                          < num_new_palette)
 681                      {
 682                         int j, next_j;
 683 
 684                         if (num_new_palette & 0x01)
 685                         {
 686                            j = p->left;
 687                            next_j = p->right;
 688                         }
 689                         else
 690                         {
 691                            j = p->right;
 692                            next_j = p->left;
 693                         }
 694 
 695                         num_new_palette--;
 696                         palette[png_ptr->index_to_palette[j]]
 697                             = palette[num_new_palette];
 698                         if (full_quantize == 0)
 699                         {
 700                            int k;
 701 
 702                            for (k = 0; k < num_palette; k++)
 703                            {
 704                               if (png_ptr->quantize_index[k] ==
 705                                   png_ptr->index_to_palette[j])
 706                                  png_ptr->quantize_index[k] =
 707                                      png_ptr->index_to_palette[next_j];
 708 
 709                               if ((int)png_ptr->quantize_index[k] ==
 710                                   num_new_palette)
 711                                  png_ptr->quantize_index[k] =
 712                                      png_ptr->index_to_palette[j];
 713                            }
 714                         }
 715 
 716                         png_ptr->index_to_palette[png_ptr->palette_to_index
 717                             [num_new_palette]] = png_ptr->index_to_palette[j];
 718 
 719                         png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
 720                             = png_ptr->palette_to_index[num_new_palette];
 721 
 722                         png_ptr->index_to_palette[j] =
 723                             (png_byte)num_new_palette;
 724 
 725                         png_ptr->palette_to_index[num_new_palette] =
 726                             (png_byte)j;
 727                      }
 728                      if (num_new_palette <= maximum_colors)
 729                         break;
 730                   }
 731                   if (num_new_palette <= maximum_colors)
 732                      break;
 733                }
 734             }
 735 
 736             for (i = 0; i < 769; i++)
 737             {
 738                if (hash[i] != NULL)
 739                {
 740                   png_dsortp p = hash[i];
 741                   while (p)
 742                   {
 743                      t = p->next;
 744                      png_free(png_ptr, p);
 745                      p = t;
 746                   }
 747                }
 748                hash[i] = 0;
 749             }
 750             max_d += 96;
 751          }
 752          png_free(png_ptr, hash);
 753          png_free(png_ptr, png_ptr->palette_to_index);
 754          png_free(png_ptr, png_ptr->index_to_palette);
 755          png_ptr->palette_to_index = NULL;
 756          png_ptr->index_to_palette = NULL;
 757       }
 758       num_palette = maximum_colors;
 759    }
 760    if (png_ptr->palette == NULL)
 761    {
 762       png_ptr->palette = palette;
 763    }
 764    png_ptr->num_palette = (png_uint_16)num_palette;
 765 
 766    if (full_quantize != 0)
 767    {
 768       int i;
 769       png_bytep distance;
 770       int total_bits = PNG_QUANTIZE_RED_BITS + PNG_QUANTIZE_GREEN_BITS +
 771           PNG_QUANTIZE_BLUE_BITS;
 772       int num_red = (1 << PNG_QUANTIZE_RED_BITS);
 773       int num_green = (1 << PNG_QUANTIZE_GREEN_BITS);
 774       int num_blue = (1 << PNG_QUANTIZE_BLUE_BITS);
 775       png_size_t num_entries = ((png_size_t)1 << total_bits);
 776 
 777       png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
 778           (png_uint_32)(num_entries * (sizeof (png_byte))));
 779 
 780       distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
 781           (sizeof (png_byte))));
 782 
 783       memset(distance, 0xff, num_entries * (sizeof (png_byte)));
 784 
 785       for (i = 0; i < num_palette; i++)
 786       {
 787          int ir, ig, ib;
 788          int r = (palette[i].red >> (8 - PNG_QUANTIZE_RED_BITS));
 789          int g = (palette[i].green >> (8 - PNG_QUANTIZE_GREEN_BITS));
 790          int b = (palette[i].blue >> (8 - PNG_QUANTIZE_BLUE_BITS));
 791 
 792          for (ir = 0; ir < num_red; ir++)
 793          {
 794             /* int dr = abs(ir - r); */
 795             int dr = ((ir > r) ? ir - r : r - ir);
 796             int index_r = (ir << (PNG_QUANTIZE_BLUE_BITS +
 797                 PNG_QUANTIZE_GREEN_BITS));
 798 
 799             for (ig = 0; ig < num_green; ig++)
 800             {
 801                /* int dg = abs(ig - g); */
 802                int dg = ((ig > g) ? ig - g : g - ig);
 803                int dt = dr + dg;
 804                int dm = ((dr > dg) ? dr : dg);
 805                int index_g = index_r | (ig << PNG_QUANTIZE_BLUE_BITS);
 806 
 807                for (ib = 0; ib < num_blue; ib++)
 808                {
 809                   int d_index = index_g | ib;
 810                   /* int db = abs(ib - b); */
 811                   int db = ((ib > b) ? ib - b : b - ib);
 812                   int dmax = ((dm > db) ? dm : db);
 813                   int d = dmax + dt + db;
 814 
 815                   if (d < (int)distance[d_index])
 816                   {
 817                      distance[d_index] = (png_byte)d;
 818                      png_ptr->palette_lookup[d_index] = (png_byte)i;
 819                   }
 820                }
 821             }
 822          }
 823       }
 824 
 825       png_free(png_ptr, distance);
 826    }
 827 }
 828 #endif /* READ_QUANTIZE */
 829 
 830 #ifdef PNG_READ_GAMMA_SUPPORTED
 831 void PNGFAPI
 832 png_set_gamma_fixed(png_structrp png_ptr, png_fixed_point scrn_gamma,
 833    png_fixed_point file_gamma)
 834 {
 835    png_debug(1, "in png_set_gamma_fixed");
 836 
 837    if (png_rtran_ok(png_ptr, 0) == 0)
 838       return;
 839 
 840    /* New in libpng-1.5.4 - reserve particular negative values as flags. */
 841    scrn_gamma = translate_gamma_flags(png_ptr, scrn_gamma, 1/*screen*/);
 842    file_gamma = translate_gamma_flags(png_ptr, file_gamma, 0/*file*/);
 843 
 844    /* Checking the gamma values for being >0 was added in 1.5.4 along with the
 845     * premultiplied alpha support; this actually hides an undocumented feature
 846     * of the previous implementation which allowed gamma processing to be
 847     * disabled in background handling.  There is no evidence (so far) that this
 848     * was being used; however, png_set_background itself accepted and must still
 849     * accept '0' for the gamma value it takes, because it isn't always used.
 850     *
 851     * Since this is an API change (albeit a very minor one that removes an
 852     * undocumented API feature) the following checks were only enabled in
 853     * libpng-1.6.0.
 854     */
 855    if (file_gamma <= 0)
 856       png_error(png_ptr, "invalid file gamma in png_set_gamma");
 857 
 858    if (scrn_gamma <= 0)
 859       png_error(png_ptr, "invalid screen gamma in png_set_gamma");
 860 
 861    /* Set the gamma values unconditionally - this overrides the value in the PNG
 862     * file if a gAMA chunk was present.  png_set_alpha_mode provides a
 863     * different, easier, way to default the file gamma.
 864     */
 865    png_ptr->colorspace.gamma = file_gamma;
 866    png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
 867    png_ptr->screen_gamma = scrn_gamma;
 868 }
 869 
 870 #  ifdef PNG_FLOATING_POINT_SUPPORTED
 871 void PNGAPI
 872 png_set_gamma(png_structrp png_ptr, double scrn_gamma, double file_gamma)
 873 {
 874    png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
 875       convert_gamma_value(png_ptr, file_gamma));
 876 }
 877 #  endif /* FLOATING_POINT */
 878 #endif /* READ_GAMMA */
 879 
 880 #ifdef PNG_READ_EXPAND_SUPPORTED
 881 /* Expand paletted images to RGB, expand grayscale images of
 882  * less than 8-bit depth to 8-bit depth, and expand tRNS chunks
 883  * to alpha channels.
 884  */
 885 void PNGAPI
 886 png_set_expand(png_structrp png_ptr)
 887 {
 888    png_debug(1, "in png_set_expand");
 889 
 890    if (png_rtran_ok(png_ptr, 0) == 0)
 891       return;
 892 
 893    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
 894 }
 895 
 896 /* GRR 19990627:  the following three functions currently are identical
 897  *  to png_set_expand().  However, it is entirely reasonable that someone
 898  *  might wish to expand an indexed image to RGB but *not* expand a single,
 899  *  fully transparent palette entry to a full alpha channel--perhaps instead
 900  *  convert tRNS to the grayscale/RGB format (16-bit RGB value), or replace
 901  *  the transparent color with a particular RGB value, or drop tRNS entirely.
 902  *  IOW, a future version of the library may make the transformations flag
 903  *  a bit more fine-grained, with separate bits for each of these three
 904  *  functions.
 905  *
 906  *  More to the point, these functions make it obvious what libpng will be
 907  *  doing, whereas "expand" can (and does) mean any number of things.
 908  *
 909  *  GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
 910  *  to expand only the sample depth but not to expand the tRNS to alpha
 911  *  and its name was changed to png_set_expand_gray_1_2_4_to_8().
 912  */
 913 
 914 /* Expand paletted images to RGB. */
 915 void PNGAPI
 916 png_set_palette_to_rgb(png_structrp png_ptr)
 917 {
 918    png_debug(1, "in png_set_palette_to_rgb");
 919 
 920    if (png_rtran_ok(png_ptr, 0) == 0)
 921       return;
 922 
 923    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
 924 }
 925 
 926 /* Expand grayscale images of less than 8-bit depth to 8 bits. */
 927 void PNGAPI
 928 png_set_expand_gray_1_2_4_to_8(png_structrp png_ptr)
 929 {
 930    png_debug(1, "in png_set_expand_gray_1_2_4_to_8");
 931 
 932    if (png_rtran_ok(png_ptr, 0) == 0)
 933       return;
 934 
 935    png_ptr->transformations |= PNG_EXPAND;
 936 }
 937 
 938 /* Expand tRNS chunks to alpha channels. */
 939 void PNGAPI
 940 png_set_tRNS_to_alpha(png_structrp png_ptr)
 941 {
 942    png_debug(1, "in png_set_tRNS_to_alpha");
 943 
 944    if (png_rtran_ok(png_ptr, 0) == 0)
 945       return;
 946 
 947    png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
 948 }
 949 #endif /* READ_EXPAND */
 950 
 951 #ifdef PNG_READ_EXPAND_16_SUPPORTED
 952 /* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
 953  * it may not work correctly.)
 954  */
 955 void PNGAPI
 956 png_set_expand_16(png_structrp png_ptr)
 957 {
 958    png_debug(1, "in png_set_expand_16");
 959 
 960    if (png_rtran_ok(png_ptr, 0) == 0)
 961       return;
 962 
 963    png_ptr->transformations |= (PNG_EXPAND_16 | PNG_EXPAND | PNG_EXPAND_tRNS);
 964 }
 965 #endif
 966 
 967 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
 968 void PNGAPI
 969 png_set_gray_to_rgb(png_structrp png_ptr)
 970 {
 971    png_debug(1, "in png_set_gray_to_rgb");
 972 
 973    if (png_rtran_ok(png_ptr, 0) == 0)
 974       return;
 975 
 976    /* Because rgb must be 8 bits or more: */
 977    png_set_expand_gray_1_2_4_to_8(png_ptr);
 978    png_ptr->transformations |= PNG_GRAY_TO_RGB;
 979 }
 980 #endif
 981 
 982 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
 983 void PNGFAPI
 984 png_set_rgb_to_gray_fixed(png_structrp png_ptr, int error_action,
 985     png_fixed_point red, png_fixed_point green)
 986 {
 987    png_debug(1, "in png_set_rgb_to_gray");
 988 
 989    /* Need the IHDR here because of the check on color_type below. */
 990    /* TODO: fix this */
 991    if (png_rtran_ok(png_ptr, 1) == 0)
 992       return;
 993 
 994    switch (error_action)
 995    {
 996       case PNG_ERROR_ACTION_NONE:
 997          png_ptr->transformations |= PNG_RGB_TO_GRAY;
 998          break;
 999 
1000       case PNG_ERROR_ACTION_WARN:
1001          png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
1002          break;
1003 
1004       case PNG_ERROR_ACTION_ERROR:
1005          png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
1006          break;
1007 
1008       default:
1009          png_error(png_ptr, "invalid error action to rgb_to_gray");
1010    }
1011 
1012    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
1013 #ifdef PNG_READ_EXPAND_SUPPORTED
1014       png_ptr->transformations |= PNG_EXPAND;
1015 #else
1016    {
1017       /* Make this an error in 1.6 because otherwise the application may assume
1018        * that it just worked and get a memory overwrite.
1019        */
1020       png_error(png_ptr,
1021         "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED");
1022 
1023       /* png_ptr->transformations &= ~PNG_RGB_TO_GRAY; */
1024    }
1025 #endif
1026    {
1027       if (red >= 0 && green >= 0 && red + green <= PNG_FP_1)
1028       {
1029          png_uint_16 red_int, green_int;
1030 
1031          /* NOTE: this calculation does not round, but this behavior is retained
1032           * for consistency; the inaccuracy is very small.  The code here always
1033           * overwrites the coefficients, regardless of whether they have been
1034           * defaulted or set already.
1035           */
1036          red_int = (png_uint_16)(((png_uint_32)red*32768)/100000);
1037          green_int = (png_uint_16)(((png_uint_32)green*32768)/100000);
1038 
1039          png_ptr->rgb_to_gray_red_coeff   = red_int;
1040          png_ptr->rgb_to_gray_green_coeff = green_int;
1041          png_ptr->rgb_to_gray_coefficients_set = 1;
1042       }
1043 
1044       else
1045       {
1046          if (red >= 0 && green >= 0)
1047             png_app_warning(png_ptr,
1048                "ignoring out of range rgb_to_gray coefficients");
1049 
1050          /* Use the defaults, from the cHRM chunk if set, else the historical
1051           * values which are close to the sRGB/HDTV/ITU-Rec 709 values.  See
1052           * png_do_rgb_to_gray for more discussion of the values.  In this case
1053           * the coefficients are not marked as 'set' and are not overwritten if
1054           * something has already provided a default.
1055           */
1056          if (png_ptr->rgb_to_gray_red_coeff == 0 &&
1057             png_ptr->rgb_to_gray_green_coeff == 0)
1058          {
1059             png_ptr->rgb_to_gray_red_coeff   = 6968;
1060             png_ptr->rgb_to_gray_green_coeff = 23434;
1061             /* png_ptr->rgb_to_gray_blue_coeff  = 2366; */
1062          }
1063       }
1064    }
1065 }
1066 
1067 #ifdef PNG_FLOATING_POINT_SUPPORTED
1068 /* Convert a RGB image to a grayscale of the same width.  This allows us,
1069  * for example, to convert a 24 bpp RGB image into an 8 bpp grayscale image.
1070  */
1071 
1072 void PNGAPI
1073 png_set_rgb_to_gray(png_structrp png_ptr, int error_action, double red,
1074    double green)
1075 {
1076    png_set_rgb_to_gray_fixed(png_ptr, error_action,
1077       png_fixed(png_ptr, red, "rgb to gray red coefficient"),
1078       png_fixed(png_ptr, green, "rgb to gray green coefficient"));
1079 }
1080 #endif /* FLOATING POINT */
1081 
1082 #endif /* RGB_TO_GRAY */
1083 
1084 #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
1085     defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
1086 void PNGAPI
1087 png_set_read_user_transform_fn(png_structrp png_ptr, png_user_transform_ptr
1088     read_user_transform_fn)
1089 {
1090    png_debug(1, "in png_set_read_user_transform_fn");
1091 
1092 #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
1093    png_ptr->transformations |= PNG_USER_TRANSFORM;
1094    png_ptr->read_user_transform_fn = read_user_transform_fn;
1095 #endif
1096 }
1097 #endif
1098 
1099 #ifdef PNG_READ_TRANSFORMS_SUPPORTED
1100 #ifdef PNG_READ_GAMMA_SUPPORTED
1101 /* In the case of gamma transformations only do transformations on images where
1102  * the [file] gamma and screen_gamma are not close reciprocals, otherwise it
1103  * slows things down slightly, and also needlessly introduces small errors.
1104  */
1105 static int /* PRIVATE */
1106 png_gamma_threshold(png_fixed_point screen_gamma, png_fixed_point file_gamma)
1107 {
1108    /* PNG_GAMMA_THRESHOLD is the threshold for performing gamma
1109     * correction as a difference of the overall transform from 1.0
1110     *
1111     * We want to compare the threshold with s*f - 1, if we get
1112     * overflow here it is because of wacky gamma values so we
1113     * turn on processing anyway.
1114     */
1115    png_fixed_point gtest;
1116    return !png_muldiv(&gtest, screen_gamma, file_gamma, PNG_FP_1) ||
1117        png_gamma_significant(gtest);
1118 }
1119 #endif
1120 
1121 /* Initialize everything needed for the read.  This includes modifying
1122  * the palette.
1123  */
1124 
1125 /* For the moment 'png_init_palette_transformations' and
1126  * 'png_init_rgb_transformations' only do some flag canceling optimizations.
1127  * The intent is that these two routines should have palette or rgb operations
1128  * extracted from 'png_init_read_transformations'.
1129  */
1130 static void /* PRIVATE */
1131 png_init_palette_transformations(png_structrp png_ptr)
1132 {
1133    /* Called to handle the (input) palette case.  In png_do_read_transformations
1134     * the first step is to expand the palette if requested, so this code must
1135     * take care to only make changes that are invariant with respect to the
1136     * palette expansion, or only do them if there is no expansion.
1137     *
1138     * STRIP_ALPHA has already been handled in the caller (by setting num_trans
1139     * to 0.)
1140     */
1141    int input_has_alpha = 0;
1142    int input_has_transparency = 0;
1143 
1144    if (png_ptr->num_trans > 0)
1145    {
1146       int i;
1147 
1148       /* Ignore if all the entries are opaque (unlikely!) */
1149       for (i=0; i<png_ptr->num_trans; ++i)
1150       {
1151          if (png_ptr->trans_alpha[i] == 255)
1152             continue;
1153          else if (png_ptr->trans_alpha[i] == 0)
1154             input_has_transparency = 1;
1155          else
1156          {
1157             input_has_transparency = 1;
1158             input_has_alpha = 1;
1159             break;
1160          }
1161       }
1162    }
1163 
1164    /* If no alpha we can optimize. */
1165    if (input_has_alpha == 0)
1166    {
1167       /* Any alpha means background and associative alpha processing is
1168        * required, however if the alpha is 0 or 1 throughout OPTIMIZE_ALPHA
1169        * and ENCODE_ALPHA are irrelevant.
1170        */
1171       png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
1172       png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
1173 
1174       if (input_has_transparency == 0)
1175          png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
1176    }
1177 
1178 #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
1179    /* png_set_background handling - deals with the complexity of whether the
1180     * background color is in the file format or the screen format in the case
1181     * where an 'expand' will happen.
1182     */
1183 
1184    /* The following code cannot be entered in the alpha pre-multiplication case
1185     * because PNG_BACKGROUND_EXPAND is cancelled below.
1186     */
1187    if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) != 0 &&
1188        (png_ptr->transformations & PNG_EXPAND) != 0)
1189    {
1190       {
1191          png_ptr->background.red   =
1192              png_ptr->palette[png_ptr->background.index].red;
1193          png_ptr->background.green =
1194              png_ptr->palette[png_ptr->background.index].green;
1195          png_ptr->background.blue  =
1196              png_ptr->palette[png_ptr->background.index].blue;
1197 
1198 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
1199         if ((png_ptr->transformations & PNG_INVERT_ALPHA) != 0)
1200         {
1201            if ((png_ptr->transformations & PNG_EXPAND_tRNS) == 0)
1202            {
1203               /* Invert the alpha channel (in tRNS) unless the pixels are
1204                * going to be expanded, in which case leave it for later
1205                */
1206               int i, istop = png_ptr->num_trans;
1207 
1208               for (i=0; i<istop; i++)
1209                  png_ptr->trans_alpha[i] = (png_byte)(255 -
1210                     png_ptr->trans_alpha[i]);
1211            }
1212         }
1213 #endif /* READ_INVERT_ALPHA */
1214       }
1215    } /* background expand and (therefore) no alpha association. */
1216 #endif /* READ_EXPAND && READ_BACKGROUND */
1217 }
1218 
1219 static void /* PRIVATE */
1220 png_init_rgb_transformations(png_structrp png_ptr)
1221 {
1222    /* Added to libpng-1.5.4: check the color type to determine whether there
1223     * is any alpha or transparency in the image and simply cancel the
1224     * background and alpha mode stuff if there isn't.
1225     */
1226    int input_has_alpha = (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0;
1227    int input_has_transparency = png_ptr->num_trans > 0;
1228 
1229    /* If no alpha we can optimize. */
1230    if (input_has_alpha == 0)
1231    {
1232       /* Any alpha means background and associative alpha processing is
1233        * required, however if the alpha is 0 or 1 throughout OPTIMIZE_ALPHA
1234        * and ENCODE_ALPHA are irrelevant.
1235        */
1236 #     ifdef PNG_READ_ALPHA_MODE_SUPPORTED
1237          png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
1238          png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
1239 #     endif
1240 
1241       if (input_has_transparency == 0)
1242          png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
1243    }
1244 
1245 #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
1246    /* png_set_background handling - deals with the complexity of whether the
1247     * background color is in the file format or the screen format in the case
1248     * where an 'expand' will happen.
1249     */
1250 
1251    /* The following code cannot be entered in the alpha pre-multiplication case
1252     * because PNG_BACKGROUND_EXPAND is cancelled below.
1253     */
1254    if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) != 0 &&
1255        (png_ptr->transformations & PNG_EXPAND) != 0 &&
1256        (png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0)
1257        /* i.e., GRAY or GRAY_ALPHA */
1258    {
1259       {
1260          /* Expand background and tRNS chunks */
1261          int gray = png_ptr->background.gray;
1262          int trans_gray = png_ptr->trans_color.gray;
1263 
1264          switch (png_ptr->bit_depth)
1265          {
1266             case 1:
1267                gray *= 0xff;
1268                trans_gray *= 0xff;
1269                break;
1270 
1271             case 2:
1272                gray *= 0x55;
1273                trans_gray *= 0x55;
1274                break;
1275 
1276             case 4:
1277                gray *= 0x11;
1278                trans_gray *= 0x11;
1279                break;
1280 
1281             default:
1282 
1283             case 8:
1284                /* FALL THROUGH (Already 8 bits) */
1285 
1286             case 16:
1287                /* Already a full 16 bits */
1288                break;
1289          }
1290 
1291          png_ptr->background.red = png_ptr->background.green =
1292             png_ptr->background.blue = (png_uint_16)gray;
1293 
1294          if ((png_ptr->transformations & PNG_EXPAND_tRNS) == 0)
1295          {
1296             png_ptr->trans_color.red = png_ptr->trans_color.green =
1297                png_ptr->trans_color.blue = (png_uint_16)trans_gray;
1298          }
1299       }
1300    } /* background expand and (therefore) no alpha association. */
1301 #endif /* READ_EXPAND && READ_BACKGROUND */
1302 }
1303 
1304 void /* PRIVATE */
1305 png_init_read_transformations(png_structrp png_ptr)
1306 {
1307    png_debug(1, "in png_init_read_transformations");
1308 
1309    /* This internal function is called from png_read_start_row in pngrutil.c
1310     * and it is called before the 'rowbytes' calculation is done, so the code
1311     * in here can change or update the transformations flags.
1312     *
1313     * First do updates that do not depend on the details of the PNG image data
1314     * being processed.
1315     */
1316 
1317 #ifdef PNG_READ_GAMMA_SUPPORTED
1318    /* Prior to 1.5.4 these tests were performed from png_set_gamma, 1.5.4 adds
1319     * png_set_alpha_mode and this is another source for a default file gamma so
1320     * the test needs to be performed later - here.  In addition prior to 1.5.4
1321     * the tests were repeated for the PALETTE color type here - this is no
1322     * longer necessary (and doesn't seem to have been necessary before.)
1323     */
1324    {
1325       /* The following temporary indicates if overall gamma correction is
1326        * required.
1327        */
1328       int gamma_correction = 0;
1329 
1330       if (png_ptr->colorspace.gamma != 0) /* has been set */
1331       {
1332          if (png_ptr->screen_gamma != 0) /* screen set too */
1333             gamma_correction = png_gamma_threshold(png_ptr->colorspace.gamma,
1334                png_ptr->screen_gamma);
1335 
1336          else
1337             /* Assume the output matches the input; a long time default behavior
1338              * of libpng, although the standard has nothing to say about this.
1339              */
1340             png_ptr->screen_gamma = png_reciprocal(png_ptr->colorspace.gamma);
1341       }
1342 
1343       else if (png_ptr->screen_gamma != 0)
1344          /* The converse - assume the file matches the screen, note that this
1345           * perhaps undesireable default can (from 1.5.4) be changed by calling
1346           * png_set_alpha_mode (even if the alpha handling mode isn't required
1347           * or isn't changed from the default.)
1348           */
1349          png_ptr->colorspace.gamma = png_reciprocal(png_ptr->screen_gamma);
1350 
1351       else /* neither are set */
1352          /* Just in case the following prevents any processing - file and screen
1353           * are both assumed to be linear and there is no way to introduce a
1354           * third gamma value other than png_set_background with 'UNIQUE', and,
1355           * prior to 1.5.4
1356           */
1357          png_ptr->screen_gamma = png_ptr->colorspace.gamma = PNG_FP_1;
1358 
1359       /* We have a gamma value now. */
1360       png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
1361 
1362       /* Now turn the gamma transformation on or off as appropriate.  Notice
1363        * that PNG_GAMMA just refers to the file->screen correction.  Alpha
1364        * composition may independently cause gamma correction because it needs
1365        * linear data (e.g. if the file has a gAMA chunk but the screen gamma
1366        * hasn't been specified.)  In any case this flag may get turned off in
1367        * the code immediately below if the transform can be handled outside the
1368        * row loop.
1369        */
1370       if (gamma_correction != 0)
1371          png_ptr->transformations |= PNG_GAMMA;
1372 
1373       else
1374          png_ptr->transformations &= ~PNG_GAMMA;
1375    }
1376 #endif
1377 
1378    /* Certain transformations have the effect of preventing other
1379     * transformations that happen afterward in png_do_read_transformations;
1380     * resolve the interdependencies here.  From the code of
1381     * png_do_read_transformations the order is:
1382     *
1383     *  1) PNG_EXPAND (including PNG_EXPAND_tRNS)
1384     *  2) PNG_STRIP_ALPHA (if no compose)
1385     *  3) PNG_RGB_TO_GRAY
1386     *  4) PNG_GRAY_TO_RGB iff !PNG_BACKGROUND_IS_GRAY
1387     *  5) PNG_COMPOSE
1388     *  6) PNG_GAMMA
1389     *  7) PNG_STRIP_ALPHA (if compose)
1390     *  8) PNG_ENCODE_ALPHA
1391     *  9) PNG_SCALE_16_TO_8
1392     * 10) PNG_16_TO_8
1393     * 11) PNG_QUANTIZE (converts to palette)
1394     * 12) PNG_EXPAND_16
1395     * 13) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
1396     * 14) PNG_INVERT_MONO
1397     * 15) PNG_INVERT_ALPHA
1398     * 16) PNG_SHIFT
1399     * 17) PNG_PACK
1400     * 18) PNG_BGR
1401     * 19) PNG_PACKSWAP
1402     * 20) PNG_FILLER (includes PNG_ADD_ALPHA)
1403     * 21) PNG_SWAP_ALPHA
1404     * 22) PNG_SWAP_BYTES
1405     * 23) PNG_USER_TRANSFORM [must be last]
1406     */
1407 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
1408    if ((png_ptr->transformations & PNG_STRIP_ALPHA) != 0 &&
1409        (png_ptr->transformations & PNG_COMPOSE) == 0)
1410    {
1411       /* Stripping the alpha channel happens immediately after the 'expand'
1412        * transformations, before all other transformation, so it cancels out
1413        * the alpha handling.  It has the side effect negating the effect of
1414        * PNG_EXPAND_tRNS too:
1415        */
1416       png_ptr->transformations &= ~(PNG_BACKGROUND_EXPAND | PNG_ENCODE_ALPHA |
1417          PNG_EXPAND_tRNS);
1418       png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
1419 
1420       /* Kill the tRNS chunk itself too.  Prior to 1.5.4 this did not happen
1421        * so transparency information would remain just so long as it wasn't
1422        * expanded.  This produces unexpected API changes if the set of things
1423        * that do PNG_EXPAND_tRNS changes (perfectly possible given the
1424        * documentation - which says ask for what you want, accept what you
1425        * get.)  This makes the behavior consistent from 1.5.4:
1426        */
1427       png_ptr->num_trans = 0;
1428    }
1429 #endif /* STRIP_ALPHA supported, no COMPOSE */
1430 
1431 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
1432    /* If the screen gamma is about 1.0 then the OPTIMIZE_ALPHA and ENCODE_ALPHA
1433     * settings will have no effect.
1434     */
1435    if (png_gamma_significant(png_ptr->screen_gamma) == 0)
1436    {
1437       png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
1438       png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
1439    }
1440 #endif
1441 
1442 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
1443    /* Make sure the coefficients for the rgb to gray conversion are set
1444     * appropriately.
1445     */
1446    if ((png_ptr->transformations & PNG_RGB_TO_GRAY) != 0)
1447       png_colorspace_set_rgb_coefficients(png_ptr);
1448 #endif
1449 
1450 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
1451 #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
1452    /* Detect gray background and attempt to enable optimization for
1453     * gray --> RGB case.
1454     *
1455     * Note:  if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
1456     * RGB_ALPHA (in which case need_expand is superfluous anyway), the
1457     * background color might actually be gray yet not be flagged as such.
1458     * This is not a problem for the current code, which uses
1459     * PNG_BACKGROUND_IS_GRAY only to decide when to do the
1460     * png_do_gray_to_rgb() transformation.
1461     *
1462     * TODO: this code needs to be revised to avoid the complexity and
1463     * interdependencies.  The color type of the background should be recorded in
1464     * png_set_background, along with the bit depth, then the code has a record
1465     * of exactly what color space the background is currently in.
1466     */
1467    if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) != 0)
1468    {
1469       /* PNG_BACKGROUND_EXPAND: the background is in the file color space, so if
1470        * the file was grayscale the background value is gray.
1471        */
1472       if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0)
1473          png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
1474    }
1475 
1476    else if ((png_ptr->transformations & PNG_COMPOSE) != 0)
1477    {
1478       /* PNG_COMPOSE: png_set_background was called with need_expand false,
1479        * so the color is in the color space of the output or png_set_alpha_mode
1480        * was called and the color is black.  Ignore RGB_TO_GRAY because that
1481        * happens before GRAY_TO_RGB.
1482        */
1483       if ((png_ptr->transformations & PNG_GRAY_TO_RGB) != 0)
1484       {
1485          if (png_ptr->background.red == png_ptr->background.green &&
1486              png_ptr->background.red == png_ptr->background.blue)
1487          {
1488             png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
1489             png_ptr->background.gray = png_ptr->background.red;
1490          }
1491       }
1492    }
1493 #endif /* READ_EXPAND && READ_BACKGROUND */
1494 #endif /* READ_GRAY_TO_RGB */
1495 
1496    /* For indexed PNG data (PNG_COLOR_TYPE_PALETTE) many of the transformations
1497     * can be performed directly on the palette, and some (such as rgb to gray)
1498     * can be optimized inside the palette.  This is particularly true of the
1499     * composite (background and alpha) stuff, which can be pretty much all done
1500     * in the palette even if the result is expanded to RGB or gray afterward.
1501     *
1502     * NOTE: this is Not Yet Implemented, the code behaves as in 1.5.1 and
1503     * earlier and the palette stuff is actually handled on the first row.  This
1504     * leads to the reported bug that the palette returned by png_get_PLTE is not
1505     * updated.
1506     */
1507    if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
1508       png_init_palette_transformations(png_ptr);
1509 
1510    else
1511       png_init_rgb_transformations(png_ptr);
1512 
1513 #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
1514    defined(PNG_READ_EXPAND_16_SUPPORTED)
1515    if ((png_ptr->transformations & PNG_EXPAND_16) != 0 &&
1516        (png_ptr->transformations & PNG_COMPOSE) != 0 &&
1517        (png_ptr->transformations & PNG_BACKGROUND_EXPAND) == 0 &&
1518        png_ptr->bit_depth != 16)
1519    {
1520       /* TODO: fix this.  Because the expand_16 operation is after the compose
1521        * handling the background color must be 8, not 16, bits deep, but the
1522        * application will supply a 16-bit value so reduce it here.
1523        *
1524        * The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
1525        * present, so that case is ok (until do_expand_16 is moved.)
1526        *
1527        * NOTE: this discards the low 16 bits of the user supplied background
1528        * color, but until expand_16 works properly there is no choice!
1529        */
1530 #     define CHOP(x) (x)=((png_uint_16)PNG_DIV257(x))
1531       CHOP(png_ptr->background.red);
1532       CHOP(png_ptr->background.green);
1533       CHOP(png_ptr->background.blue);
1534       CHOP(png_ptr->background.gray);
1535 #     undef CHOP
1536    }
1537 #endif /* READ_BACKGROUND && READ_EXPAND_16 */
1538 
1539 #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
1540    (defined(PNG_READ_SCALE_16_TO_8_SUPPORTED) || \
1541    defined(PNG_READ_STRIP_16_TO_8_SUPPORTED))
1542    if ((png_ptr->transformations & (PNG_16_TO_8|PNG_SCALE_16_TO_8)) != 0 &&
1543        (png_ptr->transformations & PNG_COMPOSE) != 0 &&
1544        (png_ptr->transformations & PNG_BACKGROUND_EXPAND) == 0 &&
1545        png_ptr->bit_depth == 16)
1546    {
1547       /* On the other hand, if a 16-bit file is to be reduced to 8-bits per
1548        * component this will also happen after PNG_COMPOSE and so the background
1549        * color must be pre-expanded here.
1550        *
1551        * TODO: fix this too.
1552        */
1553       png_ptr->background.red = (png_uint_16)(png_ptr->background.red * 257);
1554       png_ptr->background.green =
1555          (png_uint_16)(png_ptr->background.green * 257);
1556       png_ptr->background.blue = (png_uint_16)(png_ptr->background.blue * 257);
1557       png_ptr->background.gray = (png_uint_16)(png_ptr->background.gray * 257);
1558    }
1559 #endif
1560 
1561    /* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
1562     * background support (see the comments in scripts/pnglibconf.dfa), this
1563     * allows pre-multiplication of the alpha channel to be implemented as
1564     * compositing on black.  This is probably sub-optimal and has been done in
1565     * 1.5.4 betas simply to enable external critique and testing (i.e. to
1566     * implement the new API quickly, without lots of internal changes.)
1567     */
1568 
1569 #ifdef PNG_READ_GAMMA_SUPPORTED
1570 #  ifdef PNG_READ_BACKGROUND_SUPPORTED
1571       /* Includes ALPHA_MODE */
1572       png_ptr->background_1 = png_ptr->background;
1573 #  endif
1574 
1575    /* This needs to change - in the palette image case a whole set of tables are
1576     * built when it would be quicker to just calculate the correct value for
1577     * each palette entry directly.  Also, the test is too tricky - why check
1578     * PNG_RGB_TO_GRAY if PNG_GAMMA is not set?  The answer seems to be that
1579     * PNG_GAMMA is cancelled even if the gamma is known?  The test excludes the
1580     * PNG_COMPOSE case, so apparently if there is no *overall* gamma correction
1581     * the gamma tables will not be built even if composition is required on a
1582     * gamma encoded value.
1583     *
1584     * In 1.5.4 this is addressed below by an additional check on the individual
1585     * file gamma - if it is not 1.0 both RGB_TO_GRAY and COMPOSE need the
1586     * tables.
1587     */
1588    if ((png_ptr->transformations & PNG_GAMMA) != 0 ||
1589        ((png_ptr->transformations & PNG_RGB_TO_GRAY) != 0 &&
1590         (png_gamma_significant(png_ptr->colorspace.gamma) != 0 ||
1591          png_gamma_significant(png_ptr->screen_gamma) != 0)) ||
1592         ((png_ptr->transformations & PNG_COMPOSE) != 0 &&
1593          (png_gamma_significant(png_ptr->colorspace.gamma) != 0 ||
1594           png_gamma_significant(png_ptr->screen_gamma) != 0
1595 #  ifdef PNG_READ_BACKGROUND_SUPPORTED
1596          || (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_UNIQUE &&
1597            png_gamma_significant(png_ptr->background_gamma) != 0)
1598 #  endif
1599         )) || ((png_ptr->transformations & PNG_ENCODE_ALPHA) != 0 &&
1600        png_gamma_significant(png_ptr->screen_gamma) != 0))
1601    {
1602       png_build_gamma_table(png_ptr, png_ptr->bit_depth);
1603 
1604 #ifdef PNG_READ_BACKGROUND_SUPPORTED
1605       if ((png_ptr->transformations & PNG_COMPOSE) != 0)
1606       {
1607          /* Issue a warning about this combination: because RGB_TO_GRAY is
1608           * optimized to do the gamma transform if present yet do_background has
1609           * to do the same thing if both options are set a
1610           * double-gamma-correction happens.  This is true in all versions of
1611           * libpng to date.
1612           */
1613          if ((png_ptr->transformations & PNG_RGB_TO_GRAY) != 0)
1614             png_warning(png_ptr,
1615                "libpng does not support gamma+background+rgb_to_gray");
1616 
1617          if ((png_ptr->color_type == PNG_COLOR_TYPE_PALETTE) != 0)
1618          {
1619             /* We don't get to here unless there is a tRNS chunk with non-opaque
1620              * entries - see the checking code at the start of this function.
1621              */
1622             png_color back, back_1;
1623             png_colorp palette = png_ptr->palette;
1624             int num_palette = png_ptr->num_palette;
1625             int i;
1626             if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
1627             {
1628 
1629                back.red = png_ptr->gamma_table[png_ptr->background.red];
1630                back.green = png_ptr->gamma_table[png_ptr->background.green];
1631                back.blue = png_ptr->gamma_table[png_ptr->background.blue];
1632 
1633                back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
1634                back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
1635                back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
1636             }
1637             else
1638             {
1639                png_fixed_point g, gs;
1640 
1641                switch (png_ptr->background_gamma_type)
1642                {
1643                   case PNG_BACKGROUND_GAMMA_SCREEN:
1644                      g = (png_ptr->screen_gamma);
1645                      gs = PNG_FP_1;
1646                      break;
1647 
1648                   case PNG_BACKGROUND_GAMMA_FILE:
1649                      g = png_reciprocal(png_ptr->colorspace.gamma);
1650                      gs = png_reciprocal2(png_ptr->colorspace.gamma,
1651                         png_ptr->screen_gamma);
1652                      break;
1653 
1654                   case PNG_BACKGROUND_GAMMA_UNIQUE:
1655                      g = png_reciprocal(png_ptr->background_gamma);
1656                      gs = png_reciprocal2(png_ptr->background_gamma,
1657                         png_ptr->screen_gamma);
1658                      break;
1659                   default:
1660                      g = PNG_FP_1;    /* back_1 */
1661                      gs = PNG_FP_1;   /* back */
1662                      break;
1663                }
1664 
1665                if (png_gamma_significant(gs) != 0)
1666                {
1667                   back.red = png_gamma_8bit_correct(png_ptr->background.red,
1668                       gs);
1669                   back.green = png_gamma_8bit_correct(png_ptr->background.green,
1670                       gs);
1671                   back.blue = png_gamma_8bit_correct(png_ptr->background.blue,
1672                       gs);
1673                }
1674 
1675                else
1676                {
1677                   back.red   = (png_byte)png_ptr->background.red;
1678                   back.green = (png_byte)png_ptr->background.green;
1679                   back.blue  = (png_byte)png_ptr->background.blue;
1680                }
1681 
1682                if (png_gamma_significant(g) != 0)
1683                {
1684                   back_1.red = png_gamma_8bit_correct(png_ptr->background.red,
1685                      g);
1686                   back_1.green = png_gamma_8bit_correct(
1687                      png_ptr->background.green, g);
1688                   back_1.blue = png_gamma_8bit_correct(png_ptr->background.blue,
1689                      g);
1690                }
1691 
1692                else
1693                {
1694                   back_1.red   = (png_byte)png_ptr->background.red;
1695                   back_1.green = (png_byte)png_ptr->background.green;
1696                   back_1.blue  = (png_byte)png_ptr->background.blue;
1697                }
1698             }
1699 
1700             for (i = 0; i < num_palette; i++)
1701             {
1702                if (i < (int)png_ptr->num_trans &&
1703                    png_ptr->trans_alpha[i] != 0xff)
1704                {
1705                   if (png_ptr->trans_alpha[i] == 0)
1706                   {
1707                      palette[i] = back;
1708                   }
1709                   else /* if (png_ptr->trans_alpha[i] != 0xff) */
1710                   {
1711                      png_byte v, w;
1712 
1713                      v = png_ptr->gamma_to_1[palette[i].red];
1714                      png_composite(w, v, png_ptr->trans_alpha[i], back_1.red);
1715                      palette[i].red = png_ptr->gamma_from_1[w];
1716 
1717                      v = png_ptr->gamma_to_1[palette[i].green];
1718                      png_composite(w, v, png_ptr->trans_alpha[i], back_1.green);
1719                      palette[i].green = png_ptr->gamma_from_1[w];
1720 
1721                      v = png_ptr->gamma_to_1[palette[i].blue];
1722                      png_composite(w, v, png_ptr->trans_alpha[i], back_1.blue);
1723                      palette[i].blue = png_ptr->gamma_from_1[w];
1724                   }
1725                }
1726                else
1727                {
1728                   palette[i].red = png_ptr->gamma_table[palette[i].red];
1729                   palette[i].green = png_ptr->gamma_table[palette[i].green];
1730                   palette[i].blue = png_ptr->gamma_table[palette[i].blue];
1731                }
1732             }
1733 
1734             /* Prevent the transformations being done again.
1735              *
1736              * NOTE: this is highly dubious; it removes the transformations in
1737              * place.  This seems inconsistent with the general treatment of the
1738              * transformations elsewhere.
1739              */
1740             png_ptr->transformations &= ~(PNG_COMPOSE | PNG_GAMMA);
1741          } /* color_type == PNG_COLOR_TYPE_PALETTE */
1742 
1743          /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
1744          else /* color_type != PNG_COLOR_TYPE_PALETTE */
1745          {
1746             int gs_sig, g_sig;
1747             png_fixed_point g = PNG_FP_1;  /* Correction to linear */
1748             png_fixed_point gs = PNG_FP_1; /* Correction to screen */
1749 
1750             switch (png_ptr->background_gamma_type)
1751             {
1752                case PNG_BACKGROUND_GAMMA_SCREEN:
1753                   g = png_ptr->screen_gamma;
1754                   /* gs = PNG_FP_1; */
1755                   break;
1756 
1757                case PNG_BACKGROUND_GAMMA_FILE:
1758                   g = png_reciprocal(png_ptr->colorspace.gamma);
1759                   gs = png_reciprocal2(png_ptr->colorspace.gamma,
1760                      png_ptr->screen_gamma);
1761                   break;
1762 
1763                case PNG_BACKGROUND_GAMMA_UNIQUE:
1764                   g = png_reciprocal(png_ptr->background_gamma);
1765                   gs = png_reciprocal2(png_ptr->background_gamma,
1766                       png_ptr->screen_gamma);
1767                   break;
1768 
1769                default:
1770                   png_error(png_ptr, "invalid background gamma type");
1771             }
1772 
1773             g_sig = png_gamma_significant(g);
1774             gs_sig = png_gamma_significant(gs);
1775 
1776             if (g_sig != 0)
1777                png_ptr->background_1.gray = png_gamma_correct(png_ptr,
1778                    png_ptr->background.gray, g);
1779 
1780             if (gs_sig != 0)
1781                png_ptr->background.gray = png_gamma_correct(png_ptr,
1782                    png_ptr->background.gray, gs);
1783 
1784             if ((png_ptr->background.red != png_ptr->background.green) ||
1785                 (png_ptr->background.red != png_ptr->background.blue) ||
1786                 (png_ptr->background.red != png_ptr->background.gray))
1787             {
1788                /* RGB or RGBA with color background */
1789                if (g_sig != 0)
1790                {
1791                   png_ptr->background_1.red = png_gamma_correct(png_ptr,
1792                       png_ptr->background.red, g);
1793 
1794                   png_ptr->background_1.green = png_gamma_correct(png_ptr,
1795                       png_ptr->background.green, g);
1796 
1797                   png_ptr->background_1.blue = png_gamma_correct(png_ptr,
1798                       png_ptr->background.blue, g);
1799                }
1800 
1801                if (gs_sig != 0)
1802                {
1803                   png_ptr->background.red = png_gamma_correct(png_ptr,
1804                       png_ptr->background.red, gs);
1805 
1806                   png_ptr->background.green = png_gamma_correct(png_ptr,
1807                       png_ptr->background.green, gs);
1808 
1809                   png_ptr->background.blue = png_gamma_correct(png_ptr,
1810                       png_ptr->background.blue, gs);
1811                }
1812             }
1813 
1814             else
1815             {
1816                /* GRAY, GRAY ALPHA, RGB, or RGBA with gray background */
1817                png_ptr->background_1.red = png_ptr->background_1.green
1818                    = png_ptr->background_1.blue = png_ptr->background_1.gray;
1819 
1820                png_ptr->background.red = png_ptr->background.green
1821                    = png_ptr->background.blue = png_ptr->background.gray;
1822             }
1823 
1824             /* The background is now in screen gamma: */
1825             png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_SCREEN;
1826          } /* color_type != PNG_COLOR_TYPE_PALETTE */
1827       }/* png_ptr->transformations & PNG_BACKGROUND */
1828 
1829       else
1830       /* Transformation does not include PNG_BACKGROUND */
1831 #endif /* READ_BACKGROUND */
1832       if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE
1833 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
1834          /* RGB_TO_GRAY needs to have non-gamma-corrected values! */
1835          && ((png_ptr->transformations & PNG_EXPAND) == 0 ||
1836          (png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
1837 #endif
1838          )
1839       {
1840          png_colorp palette = png_ptr->palette;
1841          int num_palette = png_ptr->num_palette;
1842          int i;
1843 
1844          /* NOTE: there are other transformations that should probably be in
1845           * here too.
1846           */
1847          for (i = 0; i < num_palette; i++)
1848          {
1849             palette[i].red = png_ptr->gamma_table[palette[i].red];
1850             palette[i].green = png_ptr->gamma_table[palette[i].green];
1851             palette[i].blue = png_ptr->gamma_table[palette[i].blue];
1852          }
1853 
1854          /* Done the gamma correction. */
1855          png_ptr->transformations &= ~PNG_GAMMA;
1856       } /* color_type == PALETTE && !PNG_BACKGROUND transformation */
1857    }
1858 #ifdef PNG_READ_BACKGROUND_SUPPORTED
1859    else
1860 #endif
1861 #endif /* READ_GAMMA */
1862 
1863 #ifdef PNG_READ_BACKGROUND_SUPPORTED
1864    /* No GAMMA transformation (see the hanging else 4 lines above) */
1865    if ((png_ptr->transformations & PNG_COMPOSE) != 0 &&
1866        (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
1867    {
1868       int i;
1869       int istop = (int)png_ptr->num_trans;
1870       png_color back;
1871       png_colorp palette = png_ptr->palette;
1872 
1873       back.red   = (png_byte)png_ptr->background.red;
1874       back.green = (png_byte)png_ptr->background.green;
1875       back.blue  = (png_byte)png_ptr->background.blue;
1876 
1877       for (i = 0; i < istop; i++)
1878       {
1879          if (png_ptr->trans_alpha[i] == 0)
1880          {
1881             palette[i] = back;
1882          }
1883 
1884          else if (png_ptr->trans_alpha[i] != 0xff)
1885          {
1886             /* The png_composite() macro is defined in png.h */
1887             png_composite(palette[i].red, palette[i].red,
1888                 png_ptr->trans_alpha[i], back.red);
1889 
1890             png_composite(palette[i].green, palette[i].green,
1891                 png_ptr->trans_alpha[i], back.green);
1892 
1893             png_composite(palette[i].blue, palette[i].blue,
1894                 png_ptr->trans_alpha[i], back.blue);
1895          }
1896       }
1897 
1898       png_ptr->transformations &= ~PNG_COMPOSE;
1899    }
1900 #endif /* READ_BACKGROUND */
1901 
1902 #ifdef PNG_READ_SHIFT_SUPPORTED
1903    if ((png_ptr->transformations & PNG_SHIFT) != 0 &&
1904        (png_ptr->transformations & PNG_EXPAND) == 0 &&
1905        (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
1906    {
1907       int i;
1908       int istop = png_ptr->num_palette;
1909       int shift = 8 - png_ptr->sig_bit.red;
1910 
1911       png_ptr->transformations &= ~PNG_SHIFT;
1912 
1913       /* significant bits can be in the range 1 to 7 for a meaninful result, if
1914        * the number of significant bits is 0 then no shift is done (this is an
1915        * error condition which is silently ignored.)
1916        */
1917       if (shift > 0 && shift < 8)
1918          for (i=0; i<istop; ++i)
1919          {
1920             int component = png_ptr->palette[i].red;
1921 
1922             component >>= shift;
1923             png_ptr->palette[i].red = (png_byte)component;
1924          }
1925 
1926       shift = 8 - png_ptr->sig_bit.green;
1927       if (shift > 0 && shift < 8)
1928          for (i=0; i<istop; ++i)
1929          {
1930             int component = png_ptr->palette[i].green;
1931 
1932             component >>= shift;
1933             png_ptr->palette[i].green = (png_byte)component;
1934          }
1935 
1936       shift = 8 - png_ptr->sig_bit.blue;
1937       if (shift > 0 && shift < 8)
1938          for (i=0; i<istop; ++i)
1939          {
1940             int component = png_ptr->palette[i].blue;
1941 
1942             component >>= shift;
1943             png_ptr->palette[i].blue = (png_byte)component;
1944          }
1945    }
1946 #endif /* READ_SHIFT */
1947 }
1948 
1949 /* Modify the info structure to reflect the transformations.  The
1950  * info should be updated so a PNG file could be written with it,
1951  * assuming the transformations result in valid PNG data.
1952  */
1953 void /* PRIVATE */
1954 png_read_transform_info(png_structrp png_ptr, png_inforp info_ptr)
1955 {
1956    png_debug(1, "in png_read_transform_info");
1957 
1958 #ifdef PNG_READ_EXPAND_SUPPORTED
1959    if ((png_ptr->transformations & PNG_EXPAND) != 0)
1960    {
1961       if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
1962       {
1963          /* This check must match what actually happens in
1964           * png_do_expand_palette; if it ever checks the tRNS chunk to see if
1965           * it is all opaque we must do the same (at present it does not.)
1966           */
1967          if (png_ptr->num_trans > 0)
1968             info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
1969 
1970          else
1971             info_ptr->color_type = PNG_COLOR_TYPE_RGB;
1972 
1973          info_ptr->bit_depth = 8;
1974          info_ptr->num_trans = 0;
1975 
1976          if (png_ptr->palette == NULL)
1977             png_error (png_ptr, "Palette is NULL in indexed image");
1978       }
1979       else
1980       {
1981          if (png_ptr->num_trans != 0)
1982          {
1983             if ((png_ptr->transformations & PNG_EXPAND_tRNS) != 0)
1984                info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
1985          }
1986          if (info_ptr->bit_depth < 8)
1987             info_ptr->bit_depth = 8;
1988 
1989          info_ptr->num_trans = 0;
1990       }
1991    }
1992 #endif
1993 
1994 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
1995    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
1996    /* The following is almost certainly wrong unless the background value is in
1997     * the screen space!
1998     */
1999    if ((png_ptr->transformations & PNG_COMPOSE) != 0)
2000       info_ptr->background = png_ptr->background;
2001 #endif
2002 
2003 #ifdef PNG_READ_GAMMA_SUPPORTED
2004    /* The following used to be conditional on PNG_GAMMA (prior to 1.5.4),
2005     * however it seems that the code in png_init_read_transformations, which has
2006     * been called before this from png_read_update_info->png_read_start_row
2007     * sometimes does the gamma transform and cancels the flag.
2008     *
2009     * TODO: this looks wrong; the info_ptr should end up with a gamma equal to
2010     * the screen_gamma value.  The following probably results in weirdness if
2011     * the info_ptr is used by the app after the rows have been read.
2012     */
2013    info_ptr->colorspace.gamma = png_ptr->colorspace.gamma;
2014 #endif
2015 
2016    if (info_ptr->bit_depth == 16)
2017    {
2018 #  ifdef PNG_READ_16BIT_SUPPORTED
2019 #     ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
2020          if ((png_ptr->transformations & PNG_SCALE_16_TO_8) != 0)
2021             info_ptr->bit_depth = 8;
2022 #     endif
2023 
2024 #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
2025          if ((png_ptr->transformations & PNG_16_TO_8) != 0)
2026             info_ptr->bit_depth = 8;
2027 #     endif
2028 
2029 #  else
2030       /* No 16-bit support: force chopping 16-bit input down to 8, in this case
2031        * the app program can chose if both APIs are available by setting the
2032        * correct scaling to use.
2033        */
2034 #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
2035          /* For compatibility with previous versions use the strip method by
2036           * default.  This code works because if PNG_SCALE_16_TO_8 is already
2037           * set the code below will do that in preference to the chop.
2038           */
2039          png_ptr->transformations |= PNG_16_TO_8;
2040          info_ptr->bit_depth = 8;
2041 #     else
2042 
2043 #        ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
2044             png_ptr->transformations |= PNG_SCALE_16_TO_8;
2045             info_ptr->bit_depth = 8;
2046 #        else
2047 
2048             CONFIGURATION ERROR: you must enable at least one 16 to 8 method
2049 #        endif
2050 #    endif
2051 #endif /* !READ_16BIT */
2052    }
2053 
2054 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
2055    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) != 0)
2056       info_ptr->color_type = (png_byte)(info_ptr->color_type |
2057          PNG_COLOR_MASK_COLOR);
2058 #endif
2059 
2060 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
2061    if ((png_ptr->transformations & PNG_RGB_TO_GRAY) != 0)
2062       info_ptr->color_type = (png_byte)(info_ptr->color_type &
2063          ~PNG_COLOR_MASK_COLOR);
2064 #endif
2065 
2066 #ifdef PNG_READ_QUANTIZE_SUPPORTED
2067    if ((png_ptr->transformations & PNG_QUANTIZE) != 0)
2068    {
2069       if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
2070           (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
2071           png_ptr->palette_lookup != 0 && info_ptr->bit_depth == 8)
2072       {
2073          info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
2074       }
2075    }
2076 #endif
2077 
2078 #ifdef PNG_READ_EXPAND_16_SUPPORTED
2079    if ((png_ptr->transformations & PNG_EXPAND_16) != 0 &&
2080        info_ptr->bit_depth == 8 &&
2081        info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
2082    {
2083       info_ptr->bit_depth = 16;
2084    }
2085 #endif
2086 
2087 #ifdef PNG_READ_PACK_SUPPORTED
2088    if ((png_ptr->transformations & PNG_PACK) != 0 &&
2089        (info_ptr->bit_depth < 8))
2090       info_ptr->bit_depth = 8;
2091 #endif
2092 
2093    if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
2094       info_ptr->channels = 1;
2095 
2096    else if ((info_ptr->color_type & PNG_COLOR_MASK_COLOR) != 0)
2097       info_ptr->channels = 3;
2098 
2099    else
2100       info_ptr->channels = 1;
2101 
2102 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
2103    if ((png_ptr->transformations & PNG_STRIP_ALPHA) != 0)
2104    {
2105       info_ptr->color_type = (png_byte)(info_ptr->color_type &
2106          ~PNG_COLOR_MASK_ALPHA);
2107       info_ptr->num_trans = 0;
2108    }
2109 #endif
2110 
2111    if ((info_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0)
2112       info_ptr->channels++;
2113 
2114 #ifdef PNG_READ_FILLER_SUPPORTED
2115    /* STRIP_ALPHA and FILLER allowed:  MASK_ALPHA bit stripped above */
2116    if ((png_ptr->transformations & PNG_FILLER) != 0 &&
2117        (info_ptr->color_type == PNG_COLOR_TYPE_RGB ||
2118        info_ptr->color_type == PNG_COLOR_TYPE_GRAY))
2119    {
2120       info_ptr->channels++;
2121       /* If adding a true alpha channel not just filler */
2122       if ((png_ptr->transformations & PNG_ADD_ALPHA) != 0)
2123          info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
2124    }
2125 #endif
2126 
2127 #if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED) && \
2128 defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
2129    if ((png_ptr->transformations & PNG_USER_TRANSFORM) != 0)
2130    {
2131       if (png_ptr->user_transform_depth != 0)
2132          info_ptr->bit_depth = png_ptr->user_transform_depth;
2133 
2134       if (png_ptr->user_transform_channels != 0)
2135          info_ptr->channels = png_ptr->user_transform_channels;
2136    }
2137 #endif
2138 
2139    info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
2140        info_ptr->bit_depth);
2141 
2142    info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, info_ptr->width);
2143 
2144    /* Adding in 1.5.4: cache the above value in png_struct so that we can later
2145     * check in png_rowbytes that the user buffer won't get overwritten.  Note
2146     * that the field is not always set - if png_read_update_info isn't called
2147     * the application has to either not do any transforms or get the calculation
2148     * right itself.
2149     */
2150    png_ptr->info_rowbytes = info_ptr->rowbytes;
2151 
2152 #ifndef PNG_READ_EXPAND_SUPPORTED
2153    if (png_ptr != NULL)
2154       return;
2155 #endif
2156 }
2157 
2158 #ifdef PNG_READ_PACK_SUPPORTED
2159 /* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
2160  * without changing the actual values.  Thus, if you had a row with
2161  * a bit depth of 1, you would end up with bytes that only contained
2162  * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
2163  * png_do_shift() after this.
2164  */
2165 static void
2166 png_do_unpack(png_row_infop row_info, png_bytep row)
2167 {
2168    png_debug(1, "in png_do_unpack");
2169 
2170    if (row_info->bit_depth < 8)
2171    {
2172       png_uint_32 i;
2173       png_uint_32 row_width=row_info->width;
2174 
2175       switch (row_info->bit_depth)
2176       {
2177          case 1:
2178          {
2179             png_bytep sp = row + (png_size_t)((row_width - 1) >> 3);
2180             png_bytep dp = row + (png_size_t)row_width - 1;
2181             png_uint_32 shift = 7 - (int)((row_width + 7) & 0x07);
2182             for (i = 0; i < row_width; i++)
2183             {
2184                *dp = (png_byte)((*sp >> shift) & 0x01);
2185 
2186                if (shift == 7)
2187                {
2188                   shift = 0;
2189                   sp--;
2190                }
2191 
2192                else
2193                   shift++;
2194 
2195                dp--;
2196             }
2197             break;
2198          }
2199 
2200          case 2:
2201          {
2202 
2203             png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
2204             png_bytep dp = row + (png_size_t)row_width - 1;
2205             png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
2206             for (i = 0; i < row_width; i++)
2207             {
2208                *dp = (png_byte)((*sp >> shift) & 0x03);
2209 
2210                if (shift == 6)
2211                {
2212                   shift = 0;
2213                   sp--;
2214                }
2215 
2216                else
2217                   shift += 2;
2218 
2219                dp--;
2220             }
2221             break;
2222          }
2223 
2224          case 4:
2225          {
2226             png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
2227             png_bytep dp = row + (png_size_t)row_width - 1;
2228             png_uint_32 shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
2229             for (i = 0; i < row_width; i++)
2230             {
2231                *dp = (png_byte)((*sp >> shift) & 0x0f);
2232 
2233                if (shift == 4)
2234                {
2235                   shift = 0;
2236                   sp--;
2237                }
2238 
2239                else
2240                   shift = 4;
2241 
2242                dp--;
2243             }
2244             break;
2245          }
2246 
2247          default:
2248             break;
2249       }
2250       row_info->bit_depth = 8;
2251       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
2252       row_info->rowbytes = row_width * row_info->channels;
2253    }
2254 }
2255 #endif
2256 
2257 #ifdef PNG_READ_SHIFT_SUPPORTED
2258 /* Reverse the effects of png_do_shift.  This routine merely shifts the
2259  * pixels back to their significant bits values.  Thus, if you have
2260  * a row of bit depth 8, but only 5 are significant, this will shift
2261  * the values back to 0 through 31.
2262  */
2263 static void
2264 png_do_unshift(png_row_infop row_info, png_bytep row,
2265     png_const_color_8p sig_bits)
2266 {
2267    int color_type;
2268 
2269    png_debug(1, "in png_do_unshift");
2270 
2271    /* The palette case has already been handled in the _init routine. */
2272    color_type = row_info->color_type;
2273 
2274    if (color_type != PNG_COLOR_TYPE_PALETTE)
2275    {
2276       int shift[4];
2277       int channels = 0;
2278       int bit_depth = row_info->bit_depth;
2279 
2280       if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
2281       {
2282          shift[channels++] = bit_depth - sig_bits->red;
2283          shift[channels++] = bit_depth - sig_bits->green;
2284          shift[channels++] = bit_depth - sig_bits->blue;
2285       }
2286 
2287       else
2288       {
2289          shift[channels++] = bit_depth - sig_bits->gray;
2290       }
2291 
2292       if ((color_type & PNG_COLOR_MASK_ALPHA) != 0)
2293       {
2294          shift[channels++] = bit_depth - sig_bits->alpha;
2295       }
2296 
2297       {
2298          int c, have_shift;
2299 
2300          for (c = have_shift = 0; c < channels; ++c)
2301          {
2302             /* A shift of more than the bit depth is an error condition but it
2303              * gets ignored here.
2304              */
2305             if (shift[c] <= 0 || shift[c] >= bit_depth)
2306                shift[c] = 0;
2307 
2308             else
2309                have_shift = 1;
2310          }
2311 
2312          if (have_shift == 0)
2313             return;
2314       }
2315 
2316       switch (bit_depth)
2317       {
2318          default:
2319          /* Must be 1bpp gray: should not be here! */
2320             /* NOTREACHED */
2321             break;
2322 
2323          case 2:
2324          /* Must be 2bpp gray */
2325          /* assert(channels == 1 && shift[0] == 1) */
2326          {
2327             png_bytep bp = row;
2328             png_bytep bp_end = bp + row_info->rowbytes;
2329 
2330             while (bp < bp_end)
2331             {
2332                int b = (*bp >> 1) & 0x55;
2333                *bp++ = (png_byte)b;
2334             }
2335             break;
2336          }
2337 
2338          case 4:
2339          /* Must be 4bpp gray */
2340          /* assert(channels == 1) */
2341          {
2342             png_bytep bp = row;
2343             png_bytep bp_end = bp + row_info->rowbytes;
2344             int gray_shift = shift[0];
2345             int mask =  0xf >> gray_shift;
2346 
2347             mask |= mask << 4;
2348 
2349             while (bp < bp_end)
2350             {
2351                int b = (*bp >> gray_shift) & mask;
2352                *bp++ = (png_byte)b;
2353             }
2354             break;
2355          }
2356 
2357          case 8:
2358          /* Single byte components, G, GA, RGB, RGBA */
2359          {
2360             png_bytep bp = row;
2361             png_bytep bp_end = bp + row_info->rowbytes;
2362             int channel = 0;
2363 
2364             while (bp < bp_end)
2365             {
2366                int b = *bp >> shift[channel];
2367                if (++channel >= channels)
2368                   channel = 0;
2369                *bp++ = (png_byte)b;
2370             }
2371             break;
2372          }
2373 
2374 #ifdef PNG_READ_16BIT_SUPPORTED
2375          case 16:
2376          /* Double byte components, G, GA, RGB, RGBA */
2377          {
2378             png_bytep bp = row;
2379             png_bytep bp_end = bp + row_info->rowbytes;
2380             int channel = 0;
2381 
2382             while (bp < bp_end)
2383             {
2384                int value = (bp[0] << 8) + bp[1];
2385 
2386                value >>= shift[channel];
2387                if (++channel >= channels)
2388                   channel = 0;
2389                *bp++ = (png_byte)(value >> 8);
2390                *bp++ = (png_byte)value;
2391             }
2392             break;
2393          }
2394 #endif
2395       }
2396    }
2397 }
2398 #endif
2399 
2400 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
2401 /* Scale rows of bit depth 16 down to 8 accurately */
2402 static void
2403 png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
2404 {
2405    png_debug(1, "in png_do_scale_16_to_8");
2406 
2407    if (row_info->bit_depth == 16)
2408    {
2409       png_bytep sp = row; /* source */
2410       png_bytep dp = row; /* destination */
2411       png_bytep ep = sp + row_info->rowbytes; /* end+1 */
2412 
2413       while (sp < ep)
2414       {
2415          /* The input is an array of 16-bit components, these must be scaled to
2416           * 8 bits each.  For a 16-bit value V the required value (from the PNG
2417           * specification) is:
2418           *
2419           *    (V * 255) / 65535
2420           *
2421           * This reduces to round(V / 257), or floor((V + 128.5)/257)
2422           *
2423           * Represent V as the two byte value vhi.vlo.  Make a guess that the
2424           * result is the top byte of V, vhi, then the correction to this value
2425           * is:
2426           *
2427           *    error = floor(((V-vhi.vhi) + 128.5) / 257)
2428           *          = floor(((vlo-vhi) + 128.5) / 257)
2429           *
2430           * This can be approximated using integer arithmetic (and a signed
2431           * shift):
2432           *
2433           *    error = (vlo-vhi+128) >> 8;
2434           *
2435           * The approximate differs from the exact answer only when (vlo-vhi) is
2436           * 128; it then gives a correction of +1 when the exact correction is
2437           * 0.  This gives 128 errors.  The exact answer (correct for all 16-bit
2438           * input values) is:
2439           *
2440           *    error = (vlo-vhi+128)*65535 >> 24;
2441           *
2442           * An alternative arithmetic calculation which also gives no errors is:
2443           *
2444           *    (V * 255 + 32895) >> 16
2445           */
2446 
2447          png_int_32 tmp = *sp++; /* must be signed! */
2448          tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
2449          *dp++ = (png_byte)tmp;
2450       }
2451 
2452       row_info->bit_depth = 8;
2453       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
2454       row_info->rowbytes = row_info->width * row_info->channels;
2455    }
2456 }
2457 #endif
2458 
2459 #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
2460 static void
2461 /* Simply discard the low byte.  This was the default behavior prior
2462  * to libpng-1.5.4.
2463  */
2464 png_do_chop(png_row_infop row_info, png_bytep row)
2465 {
2466    png_debug(1, "in png_do_chop");
2467 
2468    if (row_info->bit_depth == 16)
2469    {
2470       png_bytep sp = row; /* source */
2471       png_bytep dp = row; /* destination */
2472       png_bytep ep = sp + row_info->rowbytes; /* end+1 */
2473 
2474       while (sp < ep)
2475       {
2476          *dp++ = *sp;
2477          sp += 2; /* skip low byte */
2478       }
2479 
2480       row_info->bit_depth = 8;
2481       row_info->pixel_depth = (png_byte)(8 * row_info->channels);
2482       row_info->rowbytes = row_info->width * row_info->channels;
2483    }
2484 }
2485 #endif
2486 
2487 #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
2488 static void
2489 png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
2490 {
2491    png_debug(1, "in png_do_read_swap_alpha");
2492 
2493    {
2494       png_uint_32 row_width = row_info->width;
2495       if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2496       {
2497          /* This converts from RGBA to ARGB */
2498          if (row_info->bit_depth == 8)
2499          {
2500             png_bytep sp = row + row_info->rowbytes;
2501             png_bytep dp = sp;
2502             png_byte save;
2503             png_uint_32 i;
2504 
2505             for (i = 0; i < row_width; i++)
2506             {
2507                save = *(--sp);
2508                *(--dp) = *(--sp);
2509                *(--dp) = *(--sp);
2510                *(--dp) = *(--sp);
2511                *(--dp) = save;
2512             }
2513          }
2514 
2515 #ifdef PNG_READ_16BIT_SUPPORTED
2516          /* This converts from RRGGBBAA to AARRGGBB */
2517          else
2518          {
2519             png_bytep sp = row + row_info->rowbytes;
2520             png_bytep dp = sp;
2521             png_byte save[2];
2522             png_uint_32 i;
2523 
2524             for (i = 0; i < row_width; i++)
2525             {
2526                save[0] = *(--sp);
2527                save[1] = *(--sp);
2528                *(--dp) = *(--sp);
2529                *(--dp) = *(--sp);
2530                *(--dp) = *(--sp);
2531                *(--dp) = *(--sp);
2532                *(--dp) = *(--sp);
2533                *(--dp) = *(--sp);
2534                *(--dp) = save[0];
2535                *(--dp) = save[1];
2536             }
2537          }
2538 #endif
2539       }
2540 
2541       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2542       {
2543          /* This converts from GA to AG */
2544          if (row_info->bit_depth == 8)
2545          {
2546             png_bytep sp = row + row_info->rowbytes;
2547             png_bytep dp = sp;
2548             png_byte save;
2549             png_uint_32 i;
2550 
2551             for (i = 0; i < row_width; i++)
2552             {
2553                save = *(--sp);
2554                *(--dp) = *(--sp);
2555                *(--dp) = save;
2556             }
2557          }
2558 
2559 #ifdef PNG_READ_16BIT_SUPPORTED
2560          /* This converts from GGAA to AAGG */
2561          else
2562          {
2563             png_bytep sp = row + row_info->rowbytes;
2564             png_bytep dp = sp;
2565             png_byte save[2];
2566             png_uint_32 i;
2567 
2568             for (i = 0; i < row_width; i++)
2569             {
2570                save[0] = *(--sp);
2571                save[1] = *(--sp);
2572                *(--dp) = *(--sp);
2573                *(--dp) = *(--sp);
2574                *(--dp) = save[0];
2575                *(--dp) = save[1];
2576             }
2577          }
2578 #endif
2579       }
2580    }
2581 }
2582 #endif
2583 
2584 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
2585 static void
2586 png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
2587 {
2588    png_uint_32 row_width;
2589    png_debug(1, "in png_do_read_invert_alpha");
2590 
2591    row_width = row_info->width;
2592    if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
2593    {
2594       if (row_info->bit_depth == 8)
2595       {
2596          /* This inverts the alpha channel in RGBA */
2597          png_bytep sp = row + row_info->rowbytes;
2598          png_bytep dp = sp;
2599          png_uint_32 i;
2600 
2601          for (i = 0; i < row_width; i++)
2602          {
2603             *(--dp) = (png_byte)(255 - *(--sp));
2604 
2605 /*          This does nothing:
2606             *(--dp) = *(--sp);
2607             *(--dp) = *(--sp);
2608             *(--dp) = *(--sp);
2609             We can replace it with:
2610 */
2611             sp-=3;
2612             dp=sp;
2613          }
2614       }
2615 
2616 #ifdef PNG_READ_16BIT_SUPPORTED
2617       /* This inverts the alpha channel in RRGGBBAA */
2618       else
2619       {
2620          png_bytep sp = row + row_info->rowbytes;
2621          png_bytep dp = sp;
2622          png_uint_32 i;
2623 
2624          for (i = 0; i < row_width; i++)
2625          {
2626             *(--dp) = (png_byte)(255 - *(--sp));
2627             *(--dp) = (png_byte)(255 - *(--sp));
2628 
2629 /*          This does nothing:
2630             *(--dp) = *(--sp);
2631             *(--dp) = *(--sp);
2632             *(--dp) = *(--sp);
2633             *(--dp) = *(--sp);
2634             *(--dp) = *(--sp);
2635             *(--dp) = *(--sp);
2636             We can replace it with:
2637 */
2638             sp-=6;
2639             dp=sp;
2640          }
2641       }
2642 #endif
2643    }
2644    else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2645    {
2646       if (row_info->bit_depth == 8)
2647       {
2648          /* This inverts the alpha channel in GA */
2649          png_bytep sp = row + row_info->rowbytes;
2650          png_bytep dp = sp;
2651          png_uint_32 i;
2652 
2653          for (i = 0; i < row_width; i++)
2654          {
2655             *(--dp) = (png_byte)(255 - *(--sp));
2656             *(--dp) = *(--sp);
2657          }
2658       }
2659 
2660 #ifdef PNG_READ_16BIT_SUPPORTED
2661       else
2662       {
2663          /* This inverts the alpha channel in GGAA */
2664          png_bytep sp  = row + row_info->rowbytes;
2665          png_bytep dp = sp;
2666          png_uint_32 i;
2667 
2668          for (i = 0; i < row_width; i++)
2669          {
2670             *(--dp) = (png_byte)(255 - *(--sp));
2671             *(--dp) = (png_byte)(255 - *(--sp));
2672 /*
2673             *(--dp) = *(--sp);
2674             *(--dp) = *(--sp);
2675 */
2676             sp-=2;
2677             dp=sp;
2678          }
2679       }
2680 #endif
2681    }
2682 }
2683 #endif
2684 
2685 #ifdef PNG_READ_FILLER_SUPPORTED
2686 /* Add filler channel if we have RGB color */
2687 static void
2688 png_do_read_filler(png_row_infop row_info, png_bytep row,
2689     png_uint_32 filler, png_uint_32 flags)
2690 {
2691    png_uint_32 i;
2692    png_uint_32 row_width = row_info->width;
2693 
2694 #ifdef PNG_READ_16BIT_SUPPORTED
2695    png_byte hi_filler = (png_byte)(filler>>8);
2696 #endif
2697    png_byte lo_filler = (png_byte)filler;
2698 
2699    png_debug(1, "in png_do_read_filler");
2700 
2701    if (
2702        row_info->color_type == PNG_COLOR_TYPE_GRAY)
2703    {
2704       if (row_info->bit_depth == 8)
2705       {
2706          if ((flags & PNG_FLAG_FILLER_AFTER) != 0)
2707          {
2708             /* This changes the data from G to GX */
2709             png_bytep sp = row + (png_size_t)row_width;
2710             png_bytep dp =  sp + (png_size_t)row_width;
2711             for (i = 1; i < row_width; i++)
2712             {
2713                *(--dp) = lo_filler;
2714                *(--dp) = *(--sp);
2715             }
2716             *(--dp) = lo_filler;
2717             row_info->channels = 2;
2718             row_info->pixel_depth = 16;
2719             row_info->rowbytes = row_width * 2;
2720          }
2721 
2722          else
2723          {
2724             /* This changes the data from G to XG */
2725             png_bytep sp = row + (png_size_t)row_width;
2726             png_bytep dp = sp  + (png_size_t)row_width;
2727             for (i = 0; i < row_width; i++)
2728             {
2729                *(--dp) = *(--sp);
2730                *(--dp) = lo_filler;
2731             }
2732             row_info->channels = 2;
2733             row_info->pixel_depth = 16;
2734             row_info->rowbytes = row_width * 2;
2735          }
2736       }
2737 
2738 #ifdef PNG_READ_16BIT_SUPPORTED
2739       else if (row_info->bit_depth == 16)
2740       {
2741          if ((flags & PNG_FLAG_FILLER_AFTER) != 0)
2742          {
2743             /* This changes the data from GG to GGXX */
2744             png_bytep sp = row + (png_size_t)row_width * 2;
2745             png_bytep dp = sp  + (png_size_t)row_width * 2;
2746             for (i = 1; i < row_width; i++)
2747             {
2748                *(--dp) = lo_filler;
2749                *(--dp) = hi_filler;
2750                *(--dp) = *(--sp);
2751                *(--dp) = *(--sp);
2752             }
2753             *(--dp) = lo_filler;
2754             *(--dp) = hi_filler;
2755             row_info->channels = 2;
2756             row_info->pixel_depth = 32;
2757             row_info->rowbytes = row_width * 4;
2758          }
2759 
2760          else
2761          {
2762             /* This changes the data from GG to XXGG */
2763             png_bytep sp = row + (png_size_t)row_width * 2;
2764             png_bytep dp = sp  + (png_size_t)row_width * 2;
2765             for (i = 0; i < row_width; i++)
2766             {
2767                *(--dp) = *(--sp);
2768                *(--dp) = *(--sp);
2769                *(--dp) = lo_filler;
2770                *(--dp) = hi_filler;
2771             }
2772             row_info->channels = 2;
2773             row_info->pixel_depth = 32;
2774             row_info->rowbytes = row_width * 4;
2775          }
2776       }
2777 #endif
2778    } /* COLOR_TYPE == GRAY */
2779    else if (row_info->color_type == PNG_COLOR_TYPE_RGB)
2780    {
2781       if (row_info->bit_depth == 8)
2782       {
2783          if ((flags & PNG_FLAG_FILLER_AFTER) != 0)
2784          {
2785             /* This changes the data from RGB to RGBX */
2786             png_bytep sp = row + (png_size_t)row_width * 3;
2787             png_bytep dp = sp  + (png_size_t)row_width;
2788             for (i = 1; i < row_width; i++)
2789             {
2790                *(--dp) = lo_filler;
2791                *(--dp) = *(--sp);
2792                *(--dp) = *(--sp);
2793                *(--dp) = *(--sp);
2794             }
2795             *(--dp) = lo_filler;
2796             row_info->channels = 4;
2797             row_info->pixel_depth = 32;
2798             row_info->rowbytes = row_width * 4;
2799          }
2800 
2801          else
2802          {
2803             /* This changes the data from RGB to XRGB */
2804             png_bytep sp = row + (png_size_t)row_width * 3;
2805             png_bytep dp = sp + (png_size_t)row_width;
2806             for (i = 0; i < row_width; i++)
2807             {
2808                *(--dp) = *(--sp);
2809                *(--dp) = *(--sp);
2810                *(--dp) = *(--sp);
2811                *(--dp) = lo_filler;
2812             }
2813             row_info->channels = 4;
2814             row_info->pixel_depth = 32;
2815             row_info->rowbytes = row_width * 4;
2816          }
2817       }
2818 
2819 #ifdef PNG_READ_16BIT_SUPPORTED
2820       else if (row_info->bit_depth == 16)
2821       {
2822          if ((flags & PNG_FLAG_FILLER_AFTER) != 0)
2823          {
2824             /* This changes the data from RRGGBB to RRGGBBXX */
2825             png_bytep sp = row + (png_size_t)row_width * 6;
2826             png_bytep dp = sp  + (png_size_t)row_width * 2;
2827             for (i = 1; i < row_width; i++)
2828             {
2829                *(--dp) = lo_filler;
2830                *(--dp) = hi_filler;
2831                *(--dp) = *(--sp);
2832                *(--dp) = *(--sp);
2833                *(--dp) = *(--sp);
2834                *(--dp) = *(--sp);
2835                *(--dp) = *(--sp);
2836                *(--dp) = *(--sp);
2837             }
2838             *(--dp) = lo_filler;
2839             *(--dp) = hi_filler;
2840             row_info->channels = 4;
2841             row_info->pixel_depth = 64;
2842             row_info->rowbytes = row_width * 8;
2843          }
2844 
2845          else
2846          {
2847             /* This changes the data from RRGGBB to XXRRGGBB */
2848             png_bytep sp = row + (png_size_t)row_width * 6;
2849             png_bytep dp = sp  + (png_size_t)row_width * 2;
2850             for (i = 0; i < row_width; i++)
2851             {
2852                *(--dp) = *(--sp);
2853                *(--dp) = *(--sp);
2854                *(--dp) = *(--sp);
2855                *(--dp) = *(--sp);
2856                *(--dp) = *(--sp);
2857                *(--dp) = *(--sp);
2858                *(--dp) = lo_filler;
2859                *(--dp) = hi_filler;
2860             }
2861 
2862             row_info->channels = 4;
2863             row_info->pixel_depth = 64;
2864             row_info->rowbytes = row_width * 8;
2865          }
2866       }
2867 #endif
2868    } /* COLOR_TYPE == RGB */
2869 }
2870 #endif
2871 
2872 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
2873 /* Expand grayscale files to RGB, with or without alpha */
2874 static void
2875 png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
2876 {
2877    png_uint_32 i;
2878    png_uint_32 row_width = row_info->width;
2879 
2880    png_debug(1, "in png_do_gray_to_rgb");
2881 
2882    if (row_info->bit_depth >= 8 &&
2883        (row_info->color_type & PNG_COLOR_MASK_COLOR) == 0)
2884    {
2885       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
2886       {
2887          if (row_info->bit_depth == 8)
2888          {
2889             /* This changes G to RGB */
2890             png_bytep sp = row + (png_size_t)row_width - 1;
2891             png_bytep dp = sp  + (png_size_t)row_width * 2;
2892             for (i = 0; i < row_width; i++)
2893             {
2894                *(dp--) = *sp;
2895                *(dp--) = *sp;
2896                *(dp--) = *(sp--);
2897             }
2898          }
2899 
2900          else
2901          {
2902             /* This changes GG to RRGGBB */
2903             png_bytep sp = row + (png_size_t)row_width * 2 - 1;
2904             png_bytep dp = sp  + (png_size_t)row_width * 4;
2905             for (i = 0; i < row_width; i++)
2906             {
2907                *(dp--) = *sp;
2908                *(dp--) = *(sp - 1);
2909                *(dp--) = *sp;
2910                *(dp--) = *(sp - 1);
2911                *(dp--) = *(sp--);
2912                *(dp--) = *(sp--);
2913             }
2914          }
2915       }
2916 
2917       else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
2918       {
2919          if (row_info->bit_depth == 8)
2920          {
2921             /* This changes GA to RGBA */
2922             png_bytep sp = row + (png_size_t)row_width * 2 - 1;
2923             png_bytep dp = sp  + (png_size_t)row_width * 2;
2924             for (i = 0; i < row_width; i++)
2925             {
2926                *(dp--) = *(sp--);
2927                *(dp--) = *sp;
2928                *(dp--) = *sp;
2929                *(dp--) = *(sp--);
2930             }
2931          }
2932 
2933          else
2934          {
2935             /* This changes GGAA to RRGGBBAA */
2936             png_bytep sp = row + (png_size_t)row_width * 4 - 1;
2937             png_bytep dp = sp  + (png_size_t)row_width * 4;
2938             for (i = 0; i < row_width; i++)
2939             {
2940                *(dp--) = *(sp--);
2941                *(dp--) = *(sp--);
2942                *(dp--) = *sp;
2943                *(dp--) = *(sp - 1);
2944                *(dp--) = *sp;
2945                *(dp--) = *(sp - 1);
2946                *(dp--) = *(sp--);
2947                *(dp--) = *(sp--);
2948             }
2949          }
2950       }
2951       row_info->channels = (png_byte)(row_info->channels + 2);
2952       row_info->color_type |= PNG_COLOR_MASK_COLOR;
2953       row_info->pixel_depth = (png_byte)(row_info->channels *
2954           row_info->bit_depth);
2955       row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
2956    }
2957 }
2958 #endif
2959 
2960 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
2961 /* Reduce RGB files to grayscale, with or without alpha
2962  * using the equation given in Poynton's ColorFAQ of 1998-01-04 at
2963  * <http://www.inforamp.net/~poynton/>  (THIS LINK IS DEAD June 2008 but
2964  * versions dated 1998 through November 2002 have been archived at
2965  * http://web.archive.org/web/20000816232553/http://www.inforamp.net/
2966  * ~poynton/notes/colour_and_gamma/ColorFAQ.txt )
2967  * Charles Poynton poynton at poynton.com
2968  *
2969  *     Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
2970  *
2971  *  which can be expressed with integers as
2972  *
2973  *     Y = (6969 * R + 23434 * G + 2365 * B)/32768
2974  *
2975  * Poynton's current link (as of January 2003 through July 2011):
2976  * <http://www.poynton.com/notes/colour_and_gamma/>
2977  * has changed the numbers slightly:
2978  *
2979  *     Y = 0.2126*R + 0.7152*G + 0.0722*B
2980  *
2981  *  which can be expressed with integers as
2982  *
2983  *     Y = (6966 * R + 23436 * G + 2366 * B)/32768
2984  *
2985  *  Historically, however, libpng uses numbers derived from the ITU-R Rec 709
2986  *  end point chromaticities and the D65 white point.  Depending on the
2987  *  precision used for the D65 white point this produces a variety of different
2988  *  numbers, however if the four decimal place value used in ITU-R Rec 709 is
2989  *  used (0.3127,0.3290) the Y calculation would be:
2990  *
2991  *     Y = (6968 * R + 23435 * G + 2366 * B)/32768
2992  *
2993  *  While this is correct the rounding results in an overflow for white, because
2994  *  the sum of the rounded coefficients is 32769, not 32768.  Consequently
2995  *  libpng uses, instead, the closest non-overflowing approximation:
2996  *
2997  *     Y = (6968 * R + 23434 * G + 2366 * B)/32768
2998  *
2999  *  Starting with libpng-1.5.5, if the image being converted has a cHRM chunk
3000  *  (including an sRGB chunk) then the chromaticities are used to calculate the
3001  *  coefficients.  See the chunk handling in pngrutil.c for more information.
3002  *
3003  *  In all cases the calculation is to be done in a linear colorspace.  If no
3004  *  gamma information is available to correct the encoding of the original RGB
3005  *  values this results in an implicit assumption that the original PNG RGB
3006  *  values were linear.
3007  *
3008  *  Other integer coefficents can be used via png_set_rgb_to_gray().  Because
3009  *  the API takes just red and green coefficients the blue coefficient is
3010  *  calculated to make the sum 32768.  This will result in different rounding
3011  *  to that used above.
3012  */
3013 static int
3014 png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
3015 
3016 {
3017    int rgb_error = 0;
3018 
3019    png_debug(1, "in png_do_rgb_to_gray");
3020 
3021    if ((row_info->color_type & PNG_COLOR_MASK_PALETTE) == 0 &&
3022        (row_info->color_type & PNG_COLOR_MASK_COLOR) != 0)
3023    {
3024       PNG_CONST png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
3025       PNG_CONST png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
3026       PNG_CONST png_uint_32 bc = 32768 - rc - gc;
3027       PNG_CONST png_uint_32 row_width = row_info->width;
3028       PNG_CONST int have_alpha =
3029          (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;
3030 
3031       if (row_info->bit_depth == 8)
3032       {
3033 #ifdef PNG_READ_GAMMA_SUPPORTED
3034          /* Notice that gamma to/from 1 are not necessarily inverses (if
3035           * there is an overall gamma correction).  Prior to 1.5.5 this code
3036           * checked the linearized values for equality; this doesn't match
3037           * the documentation, the original values must be checked.
3038           */
3039          if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
3040          {
3041             png_bytep sp = row;
3042             png_bytep dp = row;
3043             png_uint_32 i;
3044 
3045             for (i = 0; i < row_width; i++)
3046             {
3047                png_byte red   = *(sp++);
3048                png_byte green = *(sp++);
3049                png_byte blue  = *(sp++);
3050 
3051                if (red != green || red != blue)
3052                {
3053                   red = png_ptr->gamma_to_1[red];
3054                   green = png_ptr->gamma_to_1[green];
3055                   blue = png_ptr->gamma_to_1[blue];
3056 
3057                   rgb_error |= 1;
3058                   *(dp++) = png_ptr->gamma_from_1[
3059                       (rc*red + gc*green + bc*blue + 16384)>>15];
3060                }
3061 
3062                else
3063                {
3064                   /* If there is no overall correction the table will not be
3065                    * set.
3066                    */
3067                   if (png_ptr->gamma_table != NULL)
3068                      red = png_ptr->gamma_table[red];
3069 
3070                   *(dp++) = red;
3071                }
3072 
3073                if (have_alpha != 0)
3074                   *(dp++) = *(sp++);
3075             }
3076          }
3077          else
3078 #endif
3079          {
3080             png_bytep sp = row;
3081             png_bytep dp = row;
3082             png_uint_32 i;
3083 
3084             for (i = 0; i < row_width; i++)
3085             {
3086                png_byte red   = *(sp++);
3087                png_byte green = *(sp++);
3088                png_byte blue  = *(sp++);
3089 
3090                if (red != green || red != blue)
3091                {
3092                   rgb_error |= 1;
3093                   /* NOTE: this is the historical approach which simply
3094                    * truncates the results.
3095                    */
3096                   *(dp++) = (png_byte)((rc*red + gc*green + bc*blue)>>15);
3097                }
3098 
3099                else
3100                   *(dp++) = red;
3101 
3102                if (have_alpha != 0)
3103                   *(dp++) = *(sp++);
3104             }
3105          }
3106       }
3107 
3108       else /* RGB bit_depth == 16 */
3109       {
3110 #ifdef PNG_READ_GAMMA_SUPPORTED
3111          if (png_ptr->gamma_16_to_1 != NULL && png_ptr->gamma_16_from_1 != NULL)
3112          {
3113             png_bytep sp = row;
3114             png_bytep dp = row;
3115             png_uint_32 i;
3116 
3117             for (i = 0; i < row_width; i++)
3118             {
3119                png_uint_16 red, green, blue, w;
3120                png_byte hi,lo;
3121 
3122                hi=*(sp)++; lo=*(sp)++; red   = (png_uint_16)((hi << 8) | (lo));
3123                hi=*(sp)++; lo=*(sp)++; green = (png_uint_16)((hi << 8) | (lo));
3124                hi=*(sp)++; lo=*(sp)++; blue  = (png_uint_16)((hi << 8) | (lo));
3125 
3126                if (red == green && red == blue)
3127                {
3128                   if (png_ptr->gamma_16_table != NULL)
3129                      w = png_ptr->gamma_16_table[(red & 0xff)
3130                          >> png_ptr->gamma_shift][red >> 8];
3131 
3132                   else
3133                      w = red;
3134                }
3135 
3136                else
3137                {
3138                   png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red & 0xff)
3139                       >> png_ptr->gamma_shift][red>>8];
3140                   png_uint_16 green_1 =
3141                       png_ptr->gamma_16_to_1[(green & 0xff) >>
3142                       png_ptr->gamma_shift][green>>8];
3143                   png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue & 0xff)
3144                       >> png_ptr->gamma_shift][blue>>8];
3145                   png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
3146                       + bc*blue_1 + 16384)>>15);
3147                   w = png_ptr->gamma_16_from_1[(gray16 & 0xff) >>
3148                       png_ptr->gamma_shift][gray16 >> 8];
3149                   rgb_error |= 1;
3150                }
3151 
3152                *(dp++) = (png_byte)((w>>8) & 0xff);
3153                *(dp++) = (png_byte)(w & 0xff);
3154 
3155                if (have_alpha != 0)
3156                {
3157                   *(dp++) = *(sp++);
3158                   *(dp++) = *(sp++);
3159                }
3160             }
3161          }
3162          else
3163 #endif
3164          {
3165             png_bytep sp = row;
3166             png_bytep dp = row;
3167             png_uint_32 i;
3168 
3169             for (i = 0; i < row_width; i++)
3170             {
3171                png_uint_16 red, green, blue, gray16;
3172                png_byte hi,lo;
3173 
3174                hi=*(sp)++; lo=*(sp)++; red   = (png_uint_16)((hi << 8) | (lo));
3175                hi=*(sp)++; lo=*(sp)++; green = (png_uint_16)((hi << 8) | (lo));
3176                hi=*(sp)++; lo=*(sp)++; blue  = (png_uint_16)((hi << 8) | (lo));
3177 
3178                if (red != green || red != blue)
3179                   rgb_error |= 1;
3180 
3181                /* From 1.5.5 in the 16-bit case do the accurate conversion even
3182                 * in the 'fast' case - this is because this is where the code
3183                 * ends up when handling linear 16-bit data.
3184                 */
3185                gray16  = (png_uint_16)((rc*red + gc*green + bc*blue + 16384) >>
3186                   15);
3187                *(dp++) = (png_byte)((gray16 >> 8) & 0xff);
3188                *(dp++) = (png_byte)(gray16 & 0xff);
3189 
3190                if (have_alpha != 0)
3191                {
3192                   *(dp++) = *(sp++);
3193                   *(dp++) = *(sp++);
3194                }
3195             }
3196          }
3197       }
3198 
3199       row_info->channels = (png_byte)(row_info->channels - 2);
3200       row_info->color_type = (png_byte)(row_info->color_type &
3201           ~PNG_COLOR_MASK_COLOR);
3202       row_info->pixel_depth = (png_byte)(row_info->channels *
3203           row_info->bit_depth);
3204       row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
3205    }
3206    return rgb_error;
3207 }
3208 #endif
3209 
3210 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
3211    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
3212 /* Replace any alpha or transparency with the supplied background color.
3213  * "background" is already in the screen gamma, while "background_1" is
3214  * at a gamma of 1.0.  Paletted files have already been taken care of.
3215  */
3216 static void
3217 png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
3218 {
3219 #ifdef PNG_READ_GAMMA_SUPPORTED
3220    png_const_bytep gamma_table = png_ptr->gamma_table;
3221    png_const_bytep gamma_from_1 = png_ptr->gamma_from_1;
3222    png_const_bytep gamma_to_1 = png_ptr->gamma_to_1;
3223    png_const_uint_16pp gamma_16 = png_ptr->gamma_16_table;
3224    png_const_uint_16pp gamma_16_from_1 = png_ptr->gamma_16_from_1;
3225    png_const_uint_16pp gamma_16_to_1 = png_ptr->gamma_16_to_1;
3226    int gamma_shift = png_ptr->gamma_shift;
3227    int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
3228 #endif
3229 
3230    png_bytep sp;
3231    png_uint_32 i;
3232    png_uint_32 row_width = row_info->width;
3233    int shift;
3234 
3235    png_debug(1, "in png_do_compose");
3236 
3237    {
3238       switch (row_info->color_type)
3239       {
3240          case PNG_COLOR_TYPE_GRAY:
3241          {
3242             switch (row_info->bit_depth)
3243             {
3244                case 1:
3245                {
3246                   sp = row;
3247                   shift = 7;
3248                   for (i = 0; i < row_width; i++)
3249                   {
3250                      if ((png_uint_16)((*sp >> shift) & 0x01)
3251                         == png_ptr->trans_color.gray)
3252                      {
3253                         unsigned int tmp = *sp & (0x7f7f >> (7 - shift));
3254                         tmp |= png_ptr->background.gray << shift;
3255                         *sp = (png_byte)(tmp & 0xff);
3256                      }
3257 
3258                      if (shift == 0)
3259                      {
3260                         shift = 7;
3261                         sp++;
3262                      }
3263 
3264                      else
3265                         shift--;
3266                   }
3267                   break;
3268                }
3269 
3270                case 2:
3271                {
3272 #ifdef PNG_READ_GAMMA_SUPPORTED
3273                   if (gamma_table != NULL)
3274                   {
3275                      sp = row;
3276                      shift = 6;
3277                      for (i = 0; i < row_width; i++)
3278                      {
3279                         if ((png_uint_16)((*sp >> shift) & 0x03)
3280                             == png_ptr->trans_color.gray)
3281                         {
3282                            unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
3283                            tmp |= png_ptr->background.gray << shift;
3284                            *sp = (png_byte)(tmp & 0xff);
3285                         }
3286 
3287                         else
3288                         {
3289                            unsigned int p = (*sp >> shift) & 0x03;
3290                            unsigned int g = (gamma_table [p | (p << 2) |
3291                                (p << 4) | (p << 6)] >> 6) & 0x03;
3292                            unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
3293                            tmp |= g << shift;
3294                            *sp = (png_byte)(tmp & 0xff);
3295                         }
3296 
3297                         if (shift == 0)
3298                         {
3299                            shift = 6;
3300                            sp++;
3301                         }
3302 
3303                         else
3304                            shift -= 2;
3305                      }
3306                   }
3307 
3308                   else
3309 #endif
3310                   {
3311                      sp = row;
3312                      shift = 6;
3313                      for (i = 0; i < row_width; i++)
3314                      {
3315                         if ((png_uint_16)((*sp >> shift) & 0x03)
3316                             == png_ptr->trans_color.gray)
3317                         {
3318                            unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
3319                            tmp |= png_ptr->background.gray << shift;
3320                            *sp = (png_byte)(tmp & 0xff);
3321                         }
3322 
3323                         if (shift == 0)
3324                         {
3325                            shift = 6;
3326                            sp++;
3327                         }
3328 
3329                         else
3330                            shift -= 2;
3331                      }
3332                   }
3333                   break;
3334                }
3335 
3336                case 4:
3337                {
3338 #ifdef PNG_READ_GAMMA_SUPPORTED
3339                   if (gamma_table != NULL)
3340                   {
3341                      sp = row;
3342                      shift = 4;
3343                      for (i = 0; i < row_width; i++)
3344                      {
3345                         if ((png_uint_16)((*sp >> shift) & 0x0f)
3346                             == png_ptr->trans_color.gray)
3347                         {
3348                            unsigned int tmp = *sp & (0x0f0f >> (4 - shift));
3349                            tmp |= png_ptr->background.gray << shift;
3350                            *sp = (png_byte)(tmp & 0xff);
3351                         }
3352 
3353                         else
3354                         {
3355                            unsigned int p = (*sp >> shift) & 0x0f;
3356                            unsigned int g = (gamma_table[p | (p << 4)] >> 4) &
3357                               0x0f;
3358                            unsigned int tmp = *sp & (0x0f0f >> (4 - shift));
3359                            tmp |= g << shift;
3360                            *sp = (png_byte)(tmp & 0xff);
3361                         }
3362 
3363                         if (shift == 0)
3364                         {
3365                            shift = 4;
3366                            sp++;
3367                         }
3368 
3369                         else
3370                            shift -= 4;
3371                      }
3372                   }
3373 
3374                   else
3375 #endif
3376                   {
3377                      sp = row;
3378                      shift = 4;
3379                      for (i = 0; i < row_width; i++)
3380                      {
3381                         if ((png_uint_16)((*sp >> shift) & 0x0f)
3382                             == png_ptr->trans_color.gray)
3383                         {
3384                            unsigned int tmp = *sp & (0x0f0f >> (4 - shift));
3385                            tmp |= png_ptr->background.gray << shift;
3386                            *sp = (png_byte)(tmp & 0xff);
3387                         }
3388 
3389                         if (shift == 0)
3390                         {
3391                            shift = 4;
3392                            sp++;
3393                         }
3394 
3395                         else
3396                            shift -= 4;
3397                      }
3398                   }
3399                   break;
3400                }
3401 
3402                case 8:
3403                {
3404 #ifdef PNG_READ_GAMMA_SUPPORTED
3405                   if (gamma_table != NULL)
3406                   {
3407                      sp = row;
3408                      for (i = 0; i < row_width; i++, sp++)
3409                      {
3410                         if (*sp == png_ptr->trans_color.gray)
3411                            *sp = (png_byte)png_ptr->background.gray;
3412 
3413                         else
3414                            *sp = gamma_table[*sp];
3415                      }
3416                   }
3417                   else
3418 #endif
3419                   {
3420                      sp = row;
3421                      for (i = 0; i < row_width; i++, sp++)
3422                      {
3423                         if (*sp == png_ptr->trans_color.gray)
3424                            *sp = (png_byte)png_ptr->background.gray;
3425                      }
3426                   }
3427                   break;
3428                }
3429 
3430                case 16:
3431                {
3432 #ifdef PNG_READ_GAMMA_SUPPORTED
3433                   if (gamma_16 != NULL)
3434                   {
3435                      sp = row;
3436                      for (i = 0; i < row_width; i++, sp += 2)
3437                      {
3438                         png_uint_16 v;
3439 
3440                         v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
3441 
3442                         if (v == png_ptr->trans_color.gray)
3443                         {
3444                            /* Background is already in screen gamma */
3445                            *sp = (png_byte)((png_ptr->background.gray >> 8)
3446                                 & 0xff);
3447                            *(sp + 1) = (png_byte)(png_ptr->background.gray
3448                                 & 0xff);
3449                         }
3450 
3451                         else
3452                         {
3453                            v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
3454                            *sp = (png_byte)((v >> 8) & 0xff);
3455                            *(sp + 1) = (png_byte)(v & 0xff);
3456                         }
3457                      }
3458                   }
3459                   else
3460 #endif
3461                   {
3462                      sp = row;
3463                      for (i = 0; i < row_width; i++, sp += 2)
3464                      {
3465                         png_uint_16 v;
3466 
3467                         v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
3468 
3469                         if (v == png_ptr->trans_color.gray)
3470                         {
3471                            *sp = (png_byte)((png_ptr->background.gray >> 8)
3472                                 & 0xff);
3473                            *(sp + 1) = (png_byte)(png_ptr->background.gray
3474                                 & 0xff);
3475                         }
3476                      }
3477                   }
3478                   break;
3479                }
3480 
3481                default:
3482                   break;
3483             }
3484             break;
3485          }
3486 
3487          case PNG_COLOR_TYPE_RGB:
3488          {
3489             if (row_info->bit_depth == 8)
3490             {
3491 #ifdef PNG_READ_GAMMA_SUPPORTED
3492                if (gamma_table != NULL)
3493                {
3494                   sp = row;
3495                   for (i = 0; i < row_width; i++, sp += 3)
3496                   {
3497                      if (*sp == png_ptr->trans_color.red &&
3498                          *(sp + 1) == png_ptr->trans_color.green &&
3499                          *(sp + 2) == png_ptr->trans_color.blue)
3500                      {
3501                         *sp = (png_byte)png_ptr->background.red;
3502                         *(sp + 1) = (png_byte)png_ptr->background.green;
3503                         *(sp + 2) = (png_byte)png_ptr->background.blue;
3504                      }
3505 
3506                      else
3507                      {
3508                         *sp = gamma_table[*sp];
3509                         *(sp + 1) = gamma_table[*(sp + 1)];
3510                         *(sp + 2) = gamma_table[*(sp + 2)];
3511                      }
3512                   }
3513                }
3514                else
3515 #endif
3516                {
3517                   sp = row;
3518                   for (i = 0; i < row_width; i++, sp += 3)
3519                   {
3520                      if (*sp == png_ptr->trans_color.red &&
3521                          *(sp + 1) == png_ptr->trans_color.green &&
3522                          *(sp + 2) == png_ptr->trans_color.blue)
3523                      {
3524                         *sp = (png_byte)png_ptr->background.red;
3525                         *(sp + 1) = (png_byte)png_ptr->background.green;
3526                         *(sp + 2) = (png_byte)png_ptr->background.blue;
3527                      }
3528                   }
3529                }
3530             }
3531             else /* if (row_info->bit_depth == 16) */
3532             {
3533 #ifdef PNG_READ_GAMMA_SUPPORTED
3534                if (gamma_16 != NULL)
3535                {
3536                   sp = row;
3537                   for (i = 0; i < row_width; i++, sp += 6)
3538                   {
3539                      png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
3540 
3541                      png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
3542                          + *(sp + 3));
3543 
3544                      png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
3545                          + *(sp + 5));
3546 
3547                      if (r == png_ptr->trans_color.red &&
3548                          g == png_ptr->trans_color.green &&
3549                          b == png_ptr->trans_color.blue)
3550                      {
3551                         /* Background is already in screen gamma */
3552                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
3553                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
3554                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
3555                                 & 0xff);
3556                         *(sp + 3) = (png_byte)(png_ptr->background.green
3557                                 & 0xff);
3558                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
3559                                 & 0xff);
3560                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
3561                      }
3562 
3563                      else
3564                      {
3565                         png_uint_16 v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
3566                         *sp = (png_byte)((v >> 8) & 0xff);
3567                         *(sp + 1) = (png_byte)(v & 0xff);
3568 
3569                         v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
3570                         *(sp + 2) = (png_byte)((v >> 8) & 0xff);
3571                         *(sp + 3) = (png_byte)(v & 0xff);
3572 
3573                         v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
3574                         *(sp + 4) = (png_byte)((v >> 8) & 0xff);
3575                         *(sp + 5) = (png_byte)(v & 0xff);
3576                      }
3577                   }
3578                }
3579 
3580                else
3581 #endif
3582                {
3583                   sp = row;
3584                   for (i = 0; i < row_width; i++, sp += 6)
3585                   {
3586                      png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
3587 
3588                      png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
3589                          + *(sp + 3));
3590 
3591                      png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
3592                          + *(sp + 5));
3593 
3594                      if (r == png_ptr->trans_color.red &&
3595                          g == png_ptr->trans_color.green &&
3596                          b == png_ptr->trans_color.blue)
3597                      {
3598                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
3599                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
3600                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
3601                                 & 0xff);
3602                         *(sp + 3) = (png_byte)(png_ptr->background.green
3603                                 & 0xff);
3604                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
3605                                 & 0xff);
3606                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
3607                      }
3608                   }
3609                }
3610             }
3611             break;
3612          }
3613 
3614          case PNG_COLOR_TYPE_GRAY_ALPHA:
3615          {
3616             if (row_info->bit_depth == 8)
3617             {
3618 #ifdef PNG_READ_GAMMA_SUPPORTED
3619                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
3620                    gamma_table != NULL)
3621                {
3622                   sp = row;
3623                   for (i = 0; i < row_width; i++, sp += 2)
3624                   {
3625                      png_uint_16 a = *(sp + 1);
3626 
3627                      if (a == 0xff)
3628                         *sp = gamma_table[*sp];
3629 
3630                      else if (a == 0)
3631                      {
3632                         /* Background is already in screen gamma */
3633                         *sp = (png_byte)png_ptr->background.gray;
3634                      }
3635 
3636                      else
3637                      {
3638                         png_byte v, w;
3639 
3640                         v = gamma_to_1[*sp];
3641                         png_composite(w, v, a, png_ptr->background_1.gray);
3642                         if (optimize == 0)
3643                            w = gamma_from_1[w];
3644                         *sp = w;
3645                      }
3646                   }
3647                }
3648                else
3649 #endif
3650                {
3651                   sp = row;
3652                   for (i = 0; i < row_width; i++, sp += 2)
3653                   {
3654                      png_byte a = *(sp + 1);
3655 
3656                      if (a == 0)
3657                         *sp = (png_byte)png_ptr->background.gray;
3658 
3659                      else if (a < 0xff)
3660                         png_composite(*sp, *sp, a, png_ptr->background.gray);
3661                   }
3662                }
3663             }
3664             else /* if (png_ptr->bit_depth == 16) */
3665             {
3666 #ifdef PNG_READ_GAMMA_SUPPORTED
3667                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
3668                    gamma_16_to_1 != NULL)
3669                {
3670                   sp = row;
3671                   for (i = 0; i < row_width; i++, sp += 4)
3672                   {
3673                      png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
3674                          + *(sp + 3));
3675 
3676                      if (a == (png_uint_16)0xffff)
3677                      {
3678                         png_uint_16 v;
3679 
3680                         v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
3681                         *sp = (png_byte)((v >> 8) & 0xff);
3682                         *(sp + 1) = (png_byte)(v & 0xff);
3683                      }
3684 
3685                      else if (a == 0)
3686                      {
3687                         /* Background is already in screen gamma */
3688                         *sp = (png_byte)((png_ptr->background.gray >> 8)
3689                                 & 0xff);
3690                         *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
3691                      }
3692 
3693                      else
3694                      {
3695                         png_uint_16 g, v, w;
3696 
3697                         g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
3698                         png_composite_16(v, g, a, png_ptr->background_1.gray);
3699                         if (optimize != 0)
3700                            w = v;
3701                         else
3702                            w = gamma_16_from_1[(v & 0xff) >>
3703                                gamma_shift][v >> 8];
3704                         *sp = (png_byte)((w >> 8) & 0xff);
3705                         *(sp + 1) = (png_byte)(w & 0xff);
3706                      }
3707                   }
3708                }
3709                else
3710 #endif
3711                {
3712                   sp = row;
3713                   for (i = 0; i < row_width; i++, sp += 4)
3714                   {
3715                      png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
3716                          + *(sp + 3));
3717 
3718                      if (a == 0)
3719                      {
3720                         *sp = (png_byte)((png_ptr->background.gray >> 8)
3721                                 & 0xff);
3722                         *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
3723                      }
3724 
3725                      else if (a < 0xffff)
3726                      {
3727                         png_uint_16 g, v;
3728 
3729                         g = (png_uint_16)(((*sp) << 8) + *(sp + 1));
3730                         png_composite_16(v, g, a, png_ptr->background.gray);
3731                         *sp = (png_byte)((v >> 8) & 0xff);
3732                         *(sp + 1) = (png_byte)(v & 0xff);
3733                      }
3734                   }
3735                }
3736             }
3737             break;
3738          }
3739 
3740          case PNG_COLOR_TYPE_RGB_ALPHA:
3741          {
3742             if (row_info->bit_depth == 8)
3743             {
3744 #ifdef PNG_READ_GAMMA_SUPPORTED
3745                if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
3746                    gamma_table != NULL)
3747                {
3748                   sp = row;
3749                   for (i = 0; i < row_width; i++, sp += 4)
3750                   {
3751                      png_byte a = *(sp + 3);
3752 
3753                      if (a == 0xff)
3754                      {
3755                         *sp = gamma_table[*sp];
3756                         *(sp + 1) = gamma_table[*(sp + 1)];
3757                         *(sp + 2) = gamma_table[*(sp + 2)];
3758                      }
3759 
3760                      else if (a == 0)
3761                      {
3762                         /* Background is already in screen gamma */
3763                         *sp = (png_byte)png_ptr->background.red;
3764                         *(sp + 1) = (png_byte)png_ptr->background.green;
3765                         *(sp + 2) = (png_byte)png_ptr->background.blue;
3766                      }
3767 
3768                      else
3769                      {
3770                         png_byte v, w;
3771 
3772                         v = gamma_to_1[*sp];
3773                         png_composite(w, v, a, png_ptr->background_1.red);
3774                         if (optimize == 0) w = gamma_from_1[w];
3775                         *sp = w;
3776 
3777                         v = gamma_to_1[*(sp + 1)];
3778                         png_composite(w, v, a, png_ptr->background_1.green);
3779                         if (optimize == 0) w = gamma_from_1[w];
3780                         *(sp + 1) = w;
3781 
3782                         v = gamma_to_1[*(sp + 2)];
3783                         png_composite(w, v, a, png_ptr->background_1.blue);
3784                         if (optimize == 0) w = gamma_from_1[w];
3785                         *(sp + 2) = w;
3786                      }
3787                   }
3788                }
3789                else
3790 #endif
3791                {
3792                   sp = row;
3793                   for (i = 0; i < row_width; i++, sp += 4)
3794                   {
3795                      png_byte a = *(sp + 3);
3796 
3797                      if (a == 0)
3798                      {
3799                         *sp = (png_byte)png_ptr->background.red;
3800                         *(sp + 1) = (png_byte)png_ptr->background.green;
3801                         *(sp + 2) = (png_byte)png_ptr->background.blue;
3802                      }
3803 
3804                      else if (a < 0xff)
3805                      {
3806                         png_composite(*sp, *sp, a, png_ptr->background.red);
3807 
3808                         png_composite(*(sp + 1), *(sp + 1), a,
3809                             png_ptr->background.green);
3810 
3811                         png_composite(*(sp + 2), *(sp + 2), a,
3812                             png_ptr->background.blue);
3813                      }
3814                   }
3815                }
3816             }
3817             else /* if (row_info->bit_depth == 16) */
3818             {
3819 #ifdef PNG_READ_GAMMA_SUPPORTED
3820                if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
3821                    gamma_16_to_1 != NULL)
3822                {
3823                   sp = row;
3824                   for (i = 0; i < row_width; i++, sp += 8)
3825                   {
3826                      png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
3827                          << 8) + (png_uint_16)(*(sp + 7)));
3828 
3829                      if (a == (png_uint_16)0xffff)
3830                      {
3831                         png_uint_16 v;
3832 
3833                         v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
3834                         *sp = (png_byte)((v >> 8) & 0xff);
3835                         *(sp + 1) = (png_byte)(v & 0xff);
3836 
3837                         v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
3838                         *(sp + 2) = (png_byte)((v >> 8) & 0xff);
3839                         *(sp + 3) = (png_byte)(v & 0xff);
3840 
3841                         v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
3842                         *(sp + 4) = (png_byte)((v >> 8) & 0xff);
3843                         *(sp + 5) = (png_byte)(v & 0xff);
3844                      }
3845 
3846                      else if (a == 0)
3847                      {
3848                         /* Background is already in screen gamma */
3849                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
3850                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
3851                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
3852                                 & 0xff);
3853                         *(sp + 3) = (png_byte)(png_ptr->background.green
3854                                 & 0xff);
3855                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
3856                                 & 0xff);
3857                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
3858                      }
3859 
3860                      else
3861                      {
3862                         png_uint_16 v, w;
3863 
3864                         v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
3865                         png_composite_16(w, v, a, png_ptr->background_1.red);
3866                         if (optimize == 0)
3867                            w = gamma_16_from_1[((w & 0xff) >> gamma_shift)][w >>
3868                                 8];
3869                         *sp = (png_byte)((w >> 8) & 0xff);
3870                         *(sp + 1) = (png_byte)(w & 0xff);
3871 
3872                         v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
3873                         png_composite_16(w, v, a, png_ptr->background_1.green);
3874                         if (optimize == 0)
3875                            w = gamma_16_from_1[((w & 0xff) >> gamma_shift)][w >>
3876                                 8];
3877 
3878                         *(sp + 2) = (png_byte)((w >> 8) & 0xff);
3879                         *(sp + 3) = (png_byte)(w & 0xff);
3880 
3881                         v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
3882                         png_composite_16(w, v, a, png_ptr->background_1.blue);
3883                         if (optimize == 0)
3884                            w = gamma_16_from_1[((w & 0xff) >> gamma_shift)][w >>
3885                                 8];
3886 
3887                         *(sp + 4) = (png_byte)((w >> 8) & 0xff);
3888                         *(sp + 5) = (png_byte)(w & 0xff);
3889                      }
3890                   }
3891                }
3892 
3893                else
3894 #endif
3895                {
3896                   sp = row;
3897                   for (i = 0; i < row_width; i++, sp += 8)
3898                   {
3899                      png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
3900                          << 8) + (png_uint_16)(*(sp + 7)));
3901 
3902                      if (a == 0)
3903                      {
3904                         *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
3905                         *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
3906                         *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
3907                                 & 0xff);
3908                         *(sp + 3) = (png_byte)(png_ptr->background.green
3909                                 & 0xff);
3910                         *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
3911                                 & 0xff);
3912                         *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
3913                      }
3914 
3915                      else if (a < 0xffff)
3916                      {
3917                         png_uint_16 v;
3918 
3919                         png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
3920                         png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
3921                             + *(sp + 3));
3922                         png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
3923                             + *(sp + 5));
3924 
3925                         png_composite_16(v, r, a, png_ptr->background.red);
3926                         *sp = (png_byte)((v >> 8) & 0xff);
3927                         *(sp + 1) = (png_byte)(v & 0xff);
3928 
3929                         png_composite_16(v, g, a, png_ptr->background.green);
3930                         *(sp + 2) = (png_byte)((v >> 8) & 0xff);
3931                         *(sp + 3) = (png_byte)(v & 0xff);
3932 
3933                         png_composite_16(v, b, a, png_ptr->background.blue);
3934                         *(sp + 4) = (png_byte)((v >> 8) & 0xff);
3935                         *(sp + 5) = (png_byte)(v & 0xff);
3936                      }
3937                   }
3938                }
3939             }
3940             break;
3941          }
3942 
3943          default:
3944             break;
3945       }
3946    }
3947 }
3948 #endif /* READ_BACKGROUND || READ_ALPHA_MODE */
3949 
3950 #ifdef PNG_READ_GAMMA_SUPPORTED
3951 /* Gamma correct the image, avoiding the alpha channel.  Make sure
3952  * you do this after you deal with the transparency issue on grayscale
3953  * or RGB images. If your bit depth is 8, use gamma_table, if it
3954  * is 16, use gamma_16_table and gamma_shift.  Build these with
3955  * build_gamma_table().
3956  */
3957 static void
3958 png_do_gamma(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
3959 {
3960    png_const_bytep gamma_table = png_ptr->gamma_table;
3961    png_const_uint_16pp gamma_16_table = png_ptr->gamma_16_table;
3962    int gamma_shift = png_ptr->gamma_shift;
3963 
3964    png_bytep sp;
3965    png_uint_32 i;
3966    png_uint_32 row_width=row_info->width;
3967 
3968    png_debug(1, "in png_do_gamma");
3969 
3970    if (((row_info->bit_depth <= 8 && gamma_table != NULL) ||
3971        (row_info->bit_depth == 16 && gamma_16_table != NULL)))
3972    {
3973       switch (row_info->color_type)
3974       {
3975          case PNG_COLOR_TYPE_RGB:
3976          {
3977             if (row_info->bit_depth == 8)
3978             {
3979                sp = row;
3980                for (i = 0; i < row_width; i++)
3981                {
3982                   *sp = gamma_table[*sp];
3983                   sp++;
3984                   *sp = gamma_table[*sp];
3985                   sp++;
3986                   *sp = gamma_table[*sp];
3987                   sp++;
3988                }
3989             }
3990 
3991             else /* if (row_info->bit_depth == 16) */
3992             {
3993                sp = row;
3994                for (i = 0; i < row_width; i++)
3995                {
3996                   png_uint_16 v;
3997 
3998                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
3999                   *sp = (png_byte)((v >> 8) & 0xff);
4000                   *(sp + 1) = (png_byte)(v & 0xff);
4001                   sp += 2;
4002 
4003                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
4004                   *sp = (png_byte)((v >> 8) & 0xff);
4005                   *(sp + 1) = (png_byte)(v & 0xff);
4006                   sp += 2;
4007 
4008                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
4009                   *sp = (png_byte)((v >> 8) & 0xff);
4010                   *(sp + 1) = (png_byte)(v & 0xff);
4011                   sp += 2;
4012                }
4013             }
4014             break;
4015          }
4016 
4017          case PNG_COLOR_TYPE_RGB_ALPHA:
4018          {
4019             if (row_info->bit_depth == 8)
4020             {
4021                sp = row;
4022                for (i = 0; i < row_width; i++)
4023                {
4024                   *sp = gamma_table[*sp];
4025                   sp++;
4026 
4027                   *sp = gamma_table[*sp];
4028                   sp++;
4029 
4030                   *sp = gamma_table[*sp];
4031                   sp++;
4032 
4033                   sp++;
4034                }
4035             }
4036 
4037             else /* if (row_info->bit_depth == 16) */
4038             {
4039                sp = row;
4040                for (i = 0; i < row_width; i++)
4041                {
4042                   png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
4043                   *sp = (png_byte)((v >> 8) & 0xff);
4044                   *(sp + 1) = (png_byte)(v & 0xff);
4045                   sp += 2;
4046 
4047                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
4048                   *sp = (png_byte)((v >> 8) & 0xff);
4049                   *(sp + 1) = (png_byte)(v & 0xff);
4050                   sp += 2;
4051 
4052                   v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
4053                   *sp = (png_byte)((v >> 8) & 0xff);
4054                   *(sp + 1) = (png_byte)(v & 0xff);
4055                   sp += 4;
4056                }
4057             }
4058             break;
4059          }
4060 
4061          case PNG_COLOR_TYPE_GRAY_ALPHA:
4062          {
4063             if (row_info->bit_depth == 8)
4064             {
4065                sp = row;
4066                for (i = 0; i < row_width; i++)
4067                {
4068                   *sp = gamma_table[*sp];
4069                   sp += 2;
4070                }
4071             }
4072 
4073             else /* if (row_info->bit_depth == 16) */
4074             {
4075                sp = row;
4076                for (i = 0; i < row_width; i++)
4077                {
4078                   png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
4079                   *sp = (png_byte)((v >> 8) & 0xff);
4080                   *(sp + 1) = (png_byte)(v & 0xff);
4081                   sp += 4;
4082                }
4083             }
4084             break;
4085          }
4086 
4087          case PNG_COLOR_TYPE_GRAY:
4088          {
4089             if (row_info->bit_depth == 2)
4090             {
4091                sp = row;
4092                for (i = 0; i < row_width; i += 4)
4093                {
4094                   int a = *sp & 0xc0;
4095                   int b = *sp & 0x30;
4096                   int c = *sp & 0x0c;
4097                   int d = *sp & 0x03;
4098 
4099                   *sp = (png_byte)(
4100                       ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
4101                       ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
4102                       ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
4103                       ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
4104                   sp++;
4105                }
4106             }
4107 
4108             if (row_info->bit_depth == 4)
4109             {
4110                sp = row;
4111                for (i = 0; i < row_width; i += 2)
4112                {
4113                   int msb = *sp & 0xf0;
4114                   int lsb = *sp & 0x0f;
4115 
4116                   *sp = (png_byte)((((int)gamma_table[msb | (msb >> 4)]) & 0xf0)
4117                       | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
4118                   sp++;
4119                }
4120             }
4121 
4122             else if (row_info->bit_depth == 8)
4123             {
4124                sp = row;
4125                for (i = 0; i < row_width; i++)
4126                {
4127                   *sp = gamma_table[*sp];
4128                   sp++;
4129                }
4130             }
4131 
4132             else if (row_info->bit_depth == 16)
4133             {
4134                sp = row;
4135                for (i = 0; i < row_width; i++)
4136                {
4137                   png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
4138                   *sp = (png_byte)((v >> 8) & 0xff);
4139                   *(sp + 1) = (png_byte)(v & 0xff);
4140                   sp += 2;
4141                }
4142             }
4143             break;
4144          }
4145 
4146          default:
4147             break;
4148       }
4149    }
4150 }
4151 #endif
4152 
4153 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
4154 /* Encode the alpha channel to the output gamma (the input channel is always
4155  * linear.)  Called only with color types that have an alpha channel.  Needs the
4156  * from_1 tables.
4157  */
4158 static void
4159 png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
4160 {
4161    png_uint_32 row_width = row_info->width;
4162 
4163    png_debug(1, "in png_do_encode_alpha");
4164 
4165    if ((row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0)
4166    {
4167       if (row_info->bit_depth == 8)
4168       {
4169          PNG_CONST png_bytep table = png_ptr->gamma_from_1;
4170 
4171          if (table != NULL)
4172          {
4173             PNG_CONST int step =
4174                (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;
4175 
4176             /* The alpha channel is the last component: */
4177             row += step - 1;
4178 
4179             for (; row_width > 0; --row_width, row += step)
4180                *row = table[*row];
4181 
4182             return;
4183          }
4184       }
4185 
4186       else if (row_info->bit_depth == 16)
4187       {
4188          PNG_CONST png_uint_16pp table = png_ptr->gamma_16_from_1;
4189          PNG_CONST int gamma_shift = png_ptr->gamma_shift;
4190 
4191          if (table != NULL)
4192          {
4193             PNG_CONST int step =
4194                (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;
4195 
4196             /* The alpha channel is the last component: */
4197             row += step - 2;
4198 
4199             for (; row_width > 0; --row_width, row += step)
4200             {
4201                png_uint_16 v;
4202 
4203                v = table[*(row + 1) >> gamma_shift][*row];
4204                *row = (png_byte)((v >> 8) & 0xff);
4205                *(row + 1) = (png_byte)(v & 0xff);
4206             }
4207 
4208             return;
4209          }
4210       }
4211    }
4212 
4213    /* Only get to here if called with a weird row_info; no harm has been done,
4214     * so just issue a warning.
4215     */
4216    png_warning(png_ptr, "png_do_encode_alpha: unexpected call");
4217 }
4218 #endif
4219 
4220 #ifdef PNG_READ_EXPAND_SUPPORTED
4221 /* Expands a palette row to an RGB or RGBA row depending
4222  * upon whether you supply trans and num_trans.
4223  */
4224 static void
4225 png_do_expand_palette(png_row_infop row_info, png_bytep row,
4226    png_const_colorp palette, png_const_bytep trans_alpha, int num_trans)
4227 {
4228    int shift, value;
4229    png_bytep sp, dp;
4230    png_uint_32 i;
4231    png_uint_32 row_width=row_info->width;
4232 
4233    png_debug(1, "in png_do_expand_palette");
4234 
4235    if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
4236    {
4237       if (row_info->bit_depth < 8)
4238       {
4239          switch (row_info->bit_depth)
4240          {
4241             case 1:
4242             {
4243                sp = row + (png_size_t)((row_width - 1) >> 3);
4244                dp = row + (png_size_t)row_width - 1;
4245                shift = 7 - (int)((row_width + 7) & 0x07);
4246                for (i = 0; i < row_width; i++)
4247                {
4248                   if ((*sp >> shift) & 0x01)
4249                      *dp = 1;
4250 
4251                   else
4252                      *dp = 0;
4253 
4254                   if (shift == 7)
4255                   {
4256                      shift = 0;
4257                      sp--;
4258                   }
4259 
4260                   else
4261                      shift++;
4262 
4263                   dp--;
4264                }
4265                break;
4266             }
4267 
4268             case 2:
4269             {
4270                sp = row + (png_size_t)((row_width - 1) >> 2);
4271                dp = row + (png_size_t)row_width - 1;
4272                shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
4273                for (i = 0; i < row_width; i++)
4274                {
4275                   value = (*sp >> shift) & 0x03;
4276                   *dp = (png_byte)value;
4277                   if (shift == 6)
4278                   {
4279                      shift = 0;
4280                      sp--;
4281                   }
4282 
4283                   else
4284                      shift += 2;
4285 
4286                   dp--;
4287                }
4288                break;
4289             }
4290 
4291             case 4:
4292             {
4293                sp = row + (png_size_t)((row_width - 1) >> 1);
4294                dp = row + (png_size_t)row_width - 1;
4295                shift = (int)((row_width & 0x01) << 2);
4296                for (i = 0; i < row_width; i++)
4297                {
4298                   value = (*sp >> shift) & 0x0f;
4299                   *dp = (png_byte)value;
4300                   if (shift == 4)
4301                   {
4302                      shift = 0;
4303                      sp--;
4304                   }
4305 
4306                   else
4307                      shift += 4;
4308 
4309                   dp--;
4310                }
4311                break;
4312             }
4313 
4314             default:
4315                break;
4316          }
4317          row_info->bit_depth = 8;
4318          row_info->pixel_depth = 8;
4319          row_info->rowbytes = row_width;
4320       }
4321 
4322       if (row_info->bit_depth == 8)
4323       {
4324          {
4325             if (num_trans > 0)
4326             {
4327                sp = row + (png_size_t)row_width - 1;
4328                dp = row + (png_size_t)(row_width << 2) - 1;
4329 
4330                for (i = 0; i < row_width; i++)
4331                {
4332                   if ((int)(*sp) >= num_trans)
4333                      *dp-- = 0xff;
4334 
4335                   else
4336                      *dp-- = trans_alpha[*sp];
4337 
4338                   *dp-- = palette[*sp].blue;
4339                   *dp-- = palette[*sp].green;
4340                   *dp-- = palette[*sp].red;
4341                   sp--;
4342                }
4343                row_info->bit_depth = 8;
4344                row_info->pixel_depth = 32;
4345                row_info->rowbytes = row_width * 4;
4346                row_info->color_type = 6;
4347                row_info->channels = 4;
4348             }
4349 
4350             else
4351             {
4352                sp = row + (png_size_t)row_width - 1;
4353                dp = row + (png_size_t)(row_width * 3) - 1;
4354 
4355                for (i = 0; i < row_width; i++)
4356                {
4357                   *dp-- = palette[*sp].blue;
4358                   *dp-- = palette[*sp].green;
4359                   *dp-- = palette[*sp].red;
4360                   sp--;
4361                }
4362 
4363                row_info->bit_depth = 8;
4364                row_info->pixel_depth = 24;
4365                row_info->rowbytes = row_width * 3;
4366                row_info->color_type = 2;
4367                row_info->channels = 3;
4368             }
4369          }
4370       }
4371    }
4372 }
4373 
4374 /* If the bit depth < 8, it is expanded to 8.  Also, if the already
4375  * expanded transparency value is supplied, an alpha channel is built.
4376  */
4377 static void
4378 png_do_expand(png_row_infop row_info, png_bytep row,
4379     png_const_color_16p trans_color)
4380 {
4381    int shift, value;
4382    png_bytep sp, dp;
4383    png_uint_32 i;
4384    png_uint_32 row_width=row_info->width;
4385 
4386    png_debug(1, "in png_do_expand");
4387 
4388    {
4389       if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
4390       {
4391          unsigned int gray = trans_color != NULL ? trans_color->gray : 0;
4392 
4393          if (row_info->bit_depth < 8)
4394          {
4395             switch (row_info->bit_depth)
4396             {
4397                case 1:
4398                {
4399                   gray = (gray & 0x01) * 0xff;
4400                   sp = row + (png_size_t)((row_width - 1) >> 3);
4401                   dp = row + (png_size_t)row_width - 1;
4402                   shift = 7 - (int)((row_width + 7) & 0x07);
4403                   for (i = 0; i < row_width; i++)
4404                   {
4405                      if ((*sp >> shift) & 0x01)
4406                         *dp = 0xff;
4407 
4408                      else
4409                         *dp = 0;
4410 
4411                      if (shift == 7)
4412                      {
4413                         shift = 0;
4414                         sp--;
4415                      }
4416 
4417                      else
4418                         shift++;
4419 
4420                      dp--;
4421                   }
4422                   break;
4423                }
4424 
4425                case 2:
4426                {
4427                   gray = (gray & 0x03) * 0x55;
4428                   sp = row + (png_size_t)((row_width - 1) >> 2);
4429                   dp = row + (png_size_t)row_width - 1;
4430                   shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
4431                   for (i = 0; i < row_width; i++)
4432                   {
4433                      value = (*sp >> shift) & 0x03;
4434                      *dp = (png_byte)(value | (value << 2) | (value << 4) |
4435                         (value << 6));
4436                      if (shift == 6)
4437                      {
4438                         shift = 0;
4439                         sp--;
4440                      }
4441 
4442                      else
4443                         shift += 2;
4444 
4445                      dp--;
4446                   }
4447                   break;
4448                }
4449 
4450                case 4:
4451                {
4452                   gray = (gray & 0x0f) * 0x11;
4453                   sp = row + (png_size_t)((row_width - 1) >> 1);
4454                   dp = row + (png_size_t)row_width - 1;
4455                   shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
4456                   for (i = 0; i < row_width; i++)
4457                   {
4458                      value = (*sp >> shift) & 0x0f;
4459                      *dp = (png_byte)(value | (value << 4));
4460                      if (shift == 4)
4461                      {
4462                         shift = 0;
4463                         sp--;
4464                      }
4465 
4466                      else
4467                         shift = 4;
4468 
4469                      dp--;
4470                   }
4471                   break;
4472                }
4473 
4474                default:
4475                   break;
4476             }
4477 
4478             row_info->bit_depth = 8;
4479             row_info->pixel_depth = 8;
4480             row_info->rowbytes = row_width;
4481          }
4482 
4483          if (trans_color != NULL)
4484          {
4485             if (row_info->bit_depth == 8)
4486             {
4487                gray = gray & 0xff;
4488                sp = row + (png_size_t)row_width - 1;
4489                dp = row + (png_size_t)(row_width << 1) - 1;
4490 
4491                for (i = 0; i < row_width; i++)
4492                {
4493                   if ((*sp & 0xffU) == gray)
4494                      *dp-- = 0;
4495 
4496                   else
4497                      *dp-- = 0xff;
4498 
4499                   *dp-- = *sp--;
4500                }
4501             }
4502 
4503             else if (row_info->bit_depth == 16)
4504             {
4505                unsigned int gray_high = (gray >> 8) & 0xff;
4506                unsigned int gray_low = gray & 0xff;
4507                sp = row + row_info->rowbytes - 1;
4508                dp = row + (row_info->rowbytes << 1) - 1;
4509                for (i = 0; i < row_width; i++)
4510                {
4511                   if ((*(sp - 1) & 0xffU) == gray_high &&
4512                       (*(sp) & 0xffU) == gray_low)
4513                   {
4514                      *dp-- = 0;
4515                      *dp-- = 0;
4516                   }
4517 
4518                   else
4519                   {
4520                      *dp-- = 0xff;
4521                      *dp-- = 0xff;
4522                   }
4523 
4524                   *dp-- = *sp--;
4525                   *dp-- = *sp--;
4526                }
4527             }
4528 
4529             row_info->color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
4530             row_info->channels = 2;
4531             row_info->pixel_depth = (png_byte)(row_info->bit_depth << 1);
4532             row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
4533                row_width);
4534          }
4535       }
4536       else if (row_info->color_type == PNG_COLOR_TYPE_RGB &&
4537           trans_color != NULL)
4538       {
4539          if (row_info->bit_depth == 8)
4540          {
4541             png_byte red = (png_byte)(trans_color->red & 0xff);
4542             png_byte green = (png_byte)(trans_color->green & 0xff);
4543             png_byte blue = (png_byte)(trans_color->blue & 0xff);
4544             sp = row + (png_size_t)row_info->rowbytes - 1;
4545             dp = row + (png_size_t)(row_width << 2) - 1;
4546             for (i = 0; i < row_width; i++)
4547             {
4548                if (*(sp - 2) == red && *(sp - 1) == green && *(sp) == blue)
4549                   *dp-- = 0;
4550 
4551                else
4552                   *dp-- = 0xff;
4553 
4554                *dp-- = *sp--;
4555                *dp-- = *sp--;
4556                *dp-- = *sp--;
4557             }
4558          }
4559          else if (row_info->bit_depth == 16)
4560          {
4561             png_byte red_high = (png_byte)((trans_color->red >> 8) & 0xff);
4562             png_byte green_high = (png_byte)((trans_color->green >> 8) & 0xff);
4563             png_byte blue_high = (png_byte)((trans_color->blue >> 8) & 0xff);
4564             png_byte red_low = (png_byte)(trans_color->red & 0xff);
4565             png_byte green_low = (png_byte)(trans_color->green & 0xff);
4566             png_byte blue_low = (png_byte)(trans_color->blue & 0xff);
4567             sp = row + row_info->rowbytes - 1;
4568             dp = row + (png_size_t)(row_width << 3) - 1;
4569             for (i = 0; i < row_width; i++)
4570             {
4571                if (*(sp - 5) == red_high &&
4572                    *(sp - 4) == red_low &&
4573                    *(sp - 3) == green_high &&
4574                    *(sp - 2) == green_low &&
4575                    *(sp - 1) == blue_high &&
4576                    *(sp    ) == blue_low)
4577                {
4578                   *dp-- = 0;
4579                   *dp-- = 0;
4580                }
4581 
4582                else
4583                {
4584                   *dp-- = 0xff;
4585                   *dp-- = 0xff;
4586                }
4587 
4588                *dp-- = *sp--;
4589                *dp-- = *sp--;
4590                *dp-- = *sp--;
4591                *dp-- = *sp--;
4592                *dp-- = *sp--;
4593                *dp-- = *sp--;
4594             }
4595          }
4596          row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
4597          row_info->channels = 4;
4598          row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
4599          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
4600       }
4601    }
4602 }
4603 #endif
4604 
4605 #ifdef PNG_READ_EXPAND_16_SUPPORTED
4606 /* If the bit depth is 8 and the color type is not a palette type expand the
4607  * whole row to 16 bits.  Has no effect otherwise.
4608  */
4609 static void
4610 png_do_expand_16(png_row_infop row_info, png_bytep row)
4611 {
4612    if (row_info->bit_depth == 8 &&
4613       row_info->color_type != PNG_COLOR_TYPE_PALETTE)
4614    {
4615       /* The row have a sequence of bytes containing [0..255] and we need
4616        * to turn it into another row containing [0..65535], to do this we
4617        * calculate:
4618        *
4619        *  (input / 255) * 65535
4620        *
4621        *  Which happens to be exactly input * 257 and this can be achieved
4622        *  simply by byte replication in place (copying backwards).
4623        */
4624       png_byte *sp = row + row_info->rowbytes; /* source, last byte + 1 */
4625       png_byte *dp = sp + row_info->rowbytes;  /* destination, end + 1 */
4626       while (dp > sp)
4627          dp[-2] = dp[-1] = *--sp, dp -= 2;
4628 
4629       row_info->rowbytes *= 2;
4630       row_info->bit_depth = 16;
4631       row_info->pixel_depth = (png_byte)(row_info->channels * 16);
4632    }
4633 }
4634 #endif
4635 
4636 #ifdef PNG_READ_QUANTIZE_SUPPORTED
4637 static void
4638 png_do_quantize(png_row_infop row_info, png_bytep row,
4639     png_const_bytep palette_lookup, png_const_bytep quantize_lookup)
4640 {
4641    png_bytep sp, dp;
4642    png_uint_32 i;
4643    png_uint_32 row_width=row_info->width;
4644 
4645    png_debug(1, "in png_do_quantize");
4646 
4647    if (row_info->bit_depth == 8)
4648    {
4649       if (row_info->color_type == PNG_COLOR_TYPE_RGB && palette_lookup)
4650       {
4651          int r, g, b, p;
4652          sp = row;
4653          dp = row;
4654          for (i = 0; i < row_width; i++)
4655          {
4656             r = *sp++;
4657             g = *sp++;
4658             b = *sp++;
4659 
4660             /* This looks real messy, but the compiler will reduce
4661              * it down to a reasonable formula.  For example, with
4662              * 5 bits per color, we get:
4663              * p = (((r >> 3) & 0x1f) << 10) |
4664              *    (((g >> 3) & 0x1f) << 5) |
4665              *    ((b >> 3) & 0x1f);
4666              */
4667             p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
4668                 ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
4669                 (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
4670                 (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
4671                 ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
4672                 (PNG_QUANTIZE_BLUE_BITS)) |
4673                 ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
4674                 ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
4675 
4676             *dp++ = palette_lookup[p];
4677          }
4678 
4679          row_info->color_type = PNG_COLOR_TYPE_PALETTE;
4680          row_info->channels = 1;
4681          row_info->pixel_depth = row_info->bit_depth;
4682          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
4683       }
4684 
4685       else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
4686          palette_lookup != NULL)
4687       {
4688          int r, g, b, p;
4689          sp = row;
4690          dp = row;
4691          for (i = 0; i < row_width; i++)
4692          {
4693             r = *sp++;
4694             g = *sp++;
4695             b = *sp++;
4696             sp++;
4697 
4698             p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
4699                 ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
4700                 (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
4701                 (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
4702                 ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
4703                 (PNG_QUANTIZE_BLUE_BITS)) |
4704                 ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
4705                 ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
4706 
4707             *dp++ = palette_lookup[p];
4708          }
4709 
4710          row_info->color_type = PNG_COLOR_TYPE_PALETTE;
4711          row_info->channels = 1;
4712          row_info->pixel_depth = row_info->bit_depth;
4713          row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
4714       }
4715 
4716       else if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
4717          quantize_lookup)
4718       {
4719          sp = row;
4720 
4721          for (i = 0; i < row_width; i++, sp++)
4722          {
4723             *sp = quantize_lookup[*sp];
4724          }
4725       }
4726    }
4727 }
4728 #endif /* READ_QUANTIZE */
4729 
4730 /* Transform the row.  The order of transformations is significant,
4731  * and is very touchy.  If you add a transformation, take care to
4732  * decide how it fits in with the other transformations here.
4733  */
4734 void /* PRIVATE */
4735 png_do_read_transformations(png_structrp png_ptr, png_row_infop row_info)
4736 {
4737    png_debug(1, "in png_do_read_transformations");
4738 
4739    if (png_ptr->row_buf == NULL)
4740    {
4741       /* Prior to 1.5.4 this output row/pass where the NULL pointer is, but this
4742        * error is incredibly rare and incredibly easy to debug without this
4743        * information.
4744        */
4745       png_error(png_ptr, "NULL row buffer");
4746    }
4747 
4748    /* The following is debugging; prior to 1.5.4 the code was never compiled in;
4749     * in 1.5.4 PNG_FLAG_DETECT_UNINITIALIZED was added and the macro
4750     * PNG_WARN_UNINITIALIZED_ROW removed.  In 1.6 the new flag is set only for
4751     * all transformations, however in practice the ROW_INIT always gets done on
4752     * demand, if necessary.
4753     */
4754    if ((png_ptr->flags & PNG_FLAG_DETECT_UNINITIALIZED) != 0 &&
4755        (png_ptr->flags & PNG_FLAG_ROW_INIT) == 0)
4756    {
4757       /* Application has failed to call either png_read_start_image() or
4758        * png_read_update_info() after setting transforms that expand pixels.
4759        * This check added to libpng-1.2.19 (but not enabled until 1.5.4).
4760        */
4761       png_error(png_ptr, "Uninitialized row");
4762    }
4763 
4764 #ifdef PNG_READ_EXPAND_SUPPORTED
4765    if ((png_ptr->transformations & PNG_EXPAND) != 0)
4766    {
4767       if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
4768       {
4769          png_do_expand_palette(row_info, png_ptr->row_buf + 1,
4770              png_ptr->palette, png_ptr->trans_alpha, png_ptr->num_trans);
4771       }
4772 
4773       else
4774       {
4775          if (png_ptr->num_trans != 0 &&
4776              (png_ptr->transformations & PNG_EXPAND_tRNS) != 0)
4777             png_do_expand(row_info, png_ptr->row_buf + 1,
4778                 &(png_ptr->trans_color));
4779 
4780          else
4781             png_do_expand(row_info, png_ptr->row_buf + 1,
4782                 NULL);
4783       }
4784    }
4785 #endif
4786 
4787 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
4788    if ((png_ptr->transformations & PNG_STRIP_ALPHA) != 0 &&
4789        (png_ptr->transformations & PNG_COMPOSE) == 0 &&
4790        (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
4791        row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
4792       png_do_strip_channel(row_info, png_ptr->row_buf + 1,
4793          0 /* at_start == false, because SWAP_ALPHA happens later */);
4794 #endif
4795 
4796 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
4797    if ((png_ptr->transformations & PNG_RGB_TO_GRAY) != 0)
4798    {
4799       int rgb_error =
4800           png_do_rgb_to_gray(png_ptr, row_info,
4801               png_ptr->row_buf + 1);
4802 
4803       if (rgb_error != 0)
4804       {
4805          png_ptr->rgb_to_gray_status=1;
4806          if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
4807              PNG_RGB_TO_GRAY_WARN)
4808             png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
4809 
4810          if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
4811              PNG_RGB_TO_GRAY_ERR)
4812             png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
4813       }
4814    }
4815 #endif
4816 
4817 /* From Andreas Dilger e-mail to png-implement, 26 March 1998:
4818  *
4819  *   In most cases, the "simple transparency" should be done prior to doing
4820  *   gray-to-RGB, or you will have to test 3x as many bytes to check if a
4821  *   pixel is transparent.  You would also need to make sure that the
4822  *   transparency information is upgraded to RGB.
4823  *
4824  *   To summarize, the current flow is:
4825  *   - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
4826  *                                   with background "in place" if transparent,
4827  *                                   convert to RGB if necessary
4828  *   - Gray + alpha -> composite with gray background and remove alpha bytes,
4829  *                                   convert to RGB if necessary
4830  *
4831  *   To support RGB backgrounds for gray images we need:
4832  *   - Gray + simple transparency -> convert to RGB + simple transparency,
4833  *                                   compare 3 or 6 bytes and composite with
4834  *                                   background "in place" if transparent
4835  *                                   (3x compare/pixel compared to doing
4836  *                                   composite with gray bkgrnd)
4837  *   - Gray + alpha -> convert to RGB + alpha, composite with background and
4838  *                                   remove alpha bytes (3x float
4839  *                                   operations/pixel compared with composite
4840  *                                   on gray background)
4841  *
4842  *  Greg's change will do this.  The reason it wasn't done before is for
4843  *  performance, as this increases the per-pixel operations.  If we would check
4844  *  in advance if the background was gray or RGB, and position the gray-to-RGB
4845  *  transform appropriately, then it would save a lot of work/time.
4846  */
4847 
4848 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
4849    /* If gray -> RGB, do so now only if background is non-gray; else do later
4850     * for performance reasons
4851     */
4852    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) != 0 &&
4853        (png_ptr->mode & PNG_BACKGROUND_IS_GRAY) == 0)
4854       png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
4855 #endif
4856 
4857 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
4858    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
4859    if ((png_ptr->transformations & PNG_COMPOSE) != 0)
4860       png_do_compose(row_info, png_ptr->row_buf + 1, png_ptr);
4861 #endif
4862 
4863 #ifdef PNG_READ_GAMMA_SUPPORTED
4864    if ((png_ptr->transformations & PNG_GAMMA) != 0 &&
4865 #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
4866       /* Because RGB_TO_GRAY does the gamma transform. */
4867       (png_ptr->transformations & PNG_RGB_TO_GRAY) == 0 &&
4868 #endif
4869 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
4870    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
4871       /* Because PNG_COMPOSE does the gamma transform if there is something to
4872        * do (if there is an alpha channel or transparency.)
4873        */
4874        !((png_ptr->transformations & PNG_COMPOSE) != 0 &&
4875        ((png_ptr->num_trans != 0) ||
4876        (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0)) &&
4877 #endif
4878       /* Because png_init_read_transformations transforms the palette, unless
4879        * RGB_TO_GRAY will do the transform.
4880        */
4881        (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
4882       png_do_gamma(row_info, png_ptr->row_buf + 1, png_ptr);
4883 #endif
4884 
4885 #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
4886    if ((png_ptr->transformations & PNG_STRIP_ALPHA) != 0 &&
4887        (png_ptr->transformations & PNG_COMPOSE) != 0 &&
4888        (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
4889        row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
4890       png_do_strip_channel(row_info, png_ptr->row_buf + 1,
4891           0 /* at_start == false, because SWAP_ALPHA happens later */);
4892 #endif
4893 
4894 #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
4895    if ((png_ptr->transformations & PNG_ENCODE_ALPHA) != 0 &&
4896        (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0)
4897       png_do_encode_alpha(row_info, png_ptr->row_buf + 1, png_ptr);
4898 #endif
4899 
4900 #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
4901    if ((png_ptr->transformations & PNG_SCALE_16_TO_8) != 0)
4902       png_do_scale_16_to_8(row_info, png_ptr->row_buf + 1);
4903 #endif
4904 
4905 #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
4906    /* There is no harm in doing both of these because only one has any effect,
4907     * by putting the 'scale' option first if the app asks for scale (either by
4908     * calling the API or in a TRANSFORM flag) this is what happens.
4909     */
4910    if ((png_ptr->transformations & PNG_16_TO_8) != 0)
4911       png_do_chop(row_info, png_ptr->row_buf + 1);
4912 #endif
4913 
4914 #ifdef PNG_READ_QUANTIZE_SUPPORTED
4915    if ((png_ptr->transformations & PNG_QUANTIZE) != 0)
4916    {
4917       png_do_quantize(row_info, png_ptr->row_buf + 1,
4918           png_ptr->palette_lookup, png_ptr->quantize_index);
4919 
4920       if (row_info->rowbytes == 0)
4921          png_error(png_ptr, "png_do_quantize returned rowbytes=0");
4922    }
4923 #endif /* READ_QUANTIZE */
4924 
4925 #ifdef PNG_READ_EXPAND_16_SUPPORTED
4926    /* Do the expansion now, after all the arithmetic has been done.  Notice
4927     * that previous transformations can handle the PNG_EXPAND_16 flag if this
4928     * is efficient (particularly true in the case of gamma correction, where
4929     * better accuracy results faster!)
4930     */
4931    if ((png_ptr->transformations & PNG_EXPAND_16) != 0)
4932       png_do_expand_16(row_info, png_ptr->row_buf + 1);
4933 #endif
4934 
4935 #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
4936    /* NOTE: moved here in 1.5.4 (from much later in this list.) */
4937    if ((png_ptr->transformations & PNG_GRAY_TO_RGB) != 0 &&
4938        (png_ptr->mode & PNG_BACKGROUND_IS_GRAY) != 0)
4939       png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
4940 #endif
4941 
4942 #ifdef PNG_READ_INVERT_SUPPORTED
4943    if ((png_ptr->transformations & PNG_INVERT_MONO) != 0)
4944       png_do_invert(row_info, png_ptr->row_buf + 1);
4945 #endif
4946 
4947 #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
4948    if ((png_ptr->transformations & PNG_INVERT_ALPHA) != 0)
4949       png_do_read_invert_alpha(row_info, png_ptr->row_buf + 1);
4950 #endif
4951 
4952 #ifdef PNG_READ_SHIFT_SUPPORTED
4953    if ((png_ptr->transformations & PNG_SHIFT) != 0)
4954       png_do_unshift(row_info, png_ptr->row_buf + 1,
4955           &(png_ptr->shift));
4956 #endif
4957 
4958 #ifdef PNG_READ_PACK_SUPPORTED
4959    if ((png_ptr->transformations & PNG_PACK) != 0)
4960       png_do_unpack(row_info, png_ptr->row_buf + 1);
4961 #endif
4962 
4963 #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
4964    /* Added at libpng-1.5.10 */
4965    if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
4966        png_ptr->num_palette_max >= 0)
4967       png_do_check_palette_indexes(png_ptr, row_info);
4968 #endif
4969 
4970 #ifdef PNG_READ_BGR_SUPPORTED
4971    if ((png_ptr->transformations & PNG_BGR) != 0)
4972       png_do_bgr(row_info, png_ptr->row_buf + 1);
4973 #endif
4974 
4975 #ifdef PNG_READ_PACKSWAP_SUPPORTED
4976    if ((png_ptr->transformations & PNG_PACKSWAP) != 0)
4977       png_do_packswap(row_info, png_ptr->row_buf + 1);
4978 #endif
4979 
4980 #ifdef PNG_READ_FILLER_SUPPORTED
4981    if ((png_ptr->transformations & PNG_FILLER) != 0)
4982       png_do_read_filler(row_info, png_ptr->row_buf + 1,
4983           (png_uint_32)png_ptr->filler, png_ptr->flags);
4984 #endif
4985 
4986 #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
4987    if ((png_ptr->transformations & PNG_SWAP_ALPHA) != 0)
4988       png_do_read_swap_alpha(row_info, png_ptr->row_buf + 1);
4989 #endif
4990 
4991 #ifdef PNG_READ_16BIT_SUPPORTED
4992 #ifdef PNG_READ_SWAP_SUPPORTED
4993    if ((png_ptr->transformations & PNG_SWAP_BYTES) != 0)
4994       png_do_swap(row_info, png_ptr->row_buf + 1);
4995 #endif
4996 #endif
4997 
4998 #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
4999    if ((png_ptr->transformations & PNG_USER_TRANSFORM) != 0)
5000    {
5001       if (png_ptr->read_user_transform_fn != NULL)
5002          (*(png_ptr->read_user_transform_fn)) /* User read transform function */
5003              (png_ptr,     /* png_ptr */
5004              row_info,     /* row_info: */
5005                 /*  png_uint_32 width;       width of row */
5006                 /*  png_size_t rowbytes;     number of bytes in row */
5007                 /*  png_byte color_type;     color type of pixels */
5008                 /*  png_byte bit_depth;      bit depth of samples */
5009                 /*  png_byte channels;       number of channels (1-4) */
5010                 /*  png_byte pixel_depth;    bits per pixel (depth*channels) */
5011              png_ptr->row_buf + 1);    /* start of pixel data for row */
5012 #ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
5013       if (png_ptr->user_transform_depth != 0)
5014          row_info->bit_depth = png_ptr->user_transform_depth;
5015 
5016       if (png_ptr->user_transform_channels != 0)
5017          row_info->channels = png_ptr->user_transform_channels;
5018 #endif
5019       row_info->pixel_depth = (png_byte)(row_info->bit_depth *
5020           row_info->channels);
5021 
5022       row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_info->width);
5023    }
5024 #endif
5025 }
5026 
5027 #endif /* READ_TRANSFORMS */
5028 #endif /* READ */