1 /*
2 * jquant1.c
3 *
4 * Copyright (C) 1991-1996, Thomas G. Lane.
5 * This file is part of the Independent JPEG Group's software.
6 * For conditions of distribution and use, see the accompanying README file.
7 *
8 * This file contains 1-pass color quantization (color mapping) routines.
9 * These routines provide mapping to a fixed color map using equally spaced
10 * color values. Optional Floyd-Steinberg or ordered dithering is available.
11 */
12
13 #define JPEG_INTERNALS
14 #include "jinclude.h"
15 #include "jpeglib.h"
16
17 #ifdef QUANT_1PASS_SUPPORTED
18
19
20 /*
21 * The main purpose of 1-pass quantization is to provide a fast, if not very
22 * high quality, colormapped output capability. A 2-pass quantizer usually
23 * gives better visual quality; however, for quantized grayscale output this
24 * quantizer is perfectly adequate. Dithering is highly recommended with this
25 * quantizer, though you can turn it off if you really want to.
26 *
27 * In 1-pass quantization the colormap must be chosen in advance of seeing the
28 * image. We use a map consisting of all combinations of Ncolors[i] color
29 * values for the i'th component. The Ncolors[] values are chosen so that
30 * their product, the total number of colors, is no more than that requested.
31 * (In most cases, the product will be somewhat less.)
32 *
33 * Since the colormap is orthogonal, the representative value for each color
34 * component can be determined without considering the other components;
35 * then these indexes can be combined into a colormap index by a standard
36 * N-dimensional-array-subscript calculation. Most of the arithmetic involved
37 * can be precalculated and stored in the lookup table colorindex[].
38 * colorindex[i][j] maps pixel value j in component i to the nearest
39 * representative value (grid plane) for that component; this index is
40 * multiplied by the array stride for component i, so that the
41 * index of the colormap entry closest to a given pixel value is just
42 * sum( colorindex[component-number][pixel-component-value] )
43 * Aside from being fast, this scheme allows for variable spacing between
44 * representative values with no additional lookup cost.
45 *
46 * If gamma correction has been applied in color conversion, it might be wise
47 * to adjust the color grid spacing so that the representative colors are
48 * equidistant in linear space. At this writing, gamma correction is not
49 * implemented by jdcolor, so nothing is done here.
50 */
51
52
53 /* Declarations for ordered dithering.
54 *
55 * We use a standard 16x16 ordered dither array. The basic concept of ordered
56 * dithering is described in many references, for instance Dale Schumacher's
57 * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
58 * In place of Schumacher's comparisons against a "threshold" value, we add a
59 * "dither" value to the input pixel and then round the result to the nearest
60 * output value. The dither value is equivalent to (0.5 - threshold) times
61 * the distance between output values. For ordered dithering, we assume that
62 * the output colors are equally spaced; if not, results will probably be
63 * worse, since the dither may be too much or too little at a given point.
64 *
65 * The normal calculation would be to form pixel value + dither, range-limit
66 * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.
67 * We can skip the separate range-limiting step by extending the colorindex
68 * table in both directions.
69 */
70
71 #define ODITHER_SIZE 16 /* dimension of dither matrix */
72 /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
73 #define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE) /* # cells in matrix */
74 #define ODITHER_MASK (ODITHER_SIZE-1) /* mask for wrapping around counters */
75
76 typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
77 typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];
78
79 static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {
80 /* Bayer's order-4 dither array. Generated by the code given in
81 * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
82 * The values in this array must range from 0 to ODITHER_CELLS-1.
83 */
84 { 0,192, 48,240, 12,204, 60,252, 3,195, 51,243, 15,207, 63,255 },
85 { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },
86 { 32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },
87 { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },
88 { 8,200, 56,248, 4,196, 52,244, 11,203, 59,251, 7,199, 55,247 },
89 { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },
90 { 40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },
91 { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },
92 { 2,194, 50,242, 14,206, 62,254, 1,193, 49,241, 13,205, 61,253 },
93 { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },
94 { 34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },
95 { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },
96 { 10,202, 58,250, 6,198, 54,246, 9,201, 57,249, 5,197, 53,245 },
97 { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },
98 { 42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },
99 { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }
100 };
101
102
103 /* Declarations for Floyd-Steinberg dithering.
104 *
105 * Errors are accumulated into the array fserrors[], at a resolution of
106 * 1/16th of a pixel count. The error at a given pixel is propagated
107 * to its not-yet-processed neighbors using the standard F-S fractions,
108 * ... (here) 7/16
109 * 3/16 5/16 1/16
110 * We work left-to-right on even rows, right-to-left on odd rows.
111 *
112 * We can get away with a single array (holding one row's worth of errors)
113 * by using it to store the current row's errors at pixel columns not yet
114 * processed, but the next row's errors at columns already processed. We
115 * need only a few extra variables to hold the errors immediately around the
116 * current column. (If we are lucky, those variables are in registers, but
117 * even if not, they're probably cheaper to access than array elements are.)
118 *
119 * The fserrors[] array is indexed [component#][position].
120 * We provide (#columns + 2) entries per component; the extra entry at each
121 * end saves us from special-casing the first and last pixels.
122 *
123 * Note: on a wide image, we might not have enough room in a PC's near data
124 * segment to hold the error array; so it is allocated with alloc_large.
125 */
126
127 #if BITS_IN_JSAMPLE == 8
128 typedef INT16 FSERROR; /* 16 bits should be enough */
129 typedef int LOCFSERROR; /* use 'int' for calculation temps */
130 #else
131 typedef INT32 FSERROR; /* may need more than 16 bits */
132 typedef INT32 LOCFSERROR; /* be sure calculation temps are big enough */
133 #endif
134
135 typedef FSERROR FAR *FSERRPTR; /* pointer to error array (in FAR storage!) */
136
137
138 /* Private subobject */
139
140 #define MAX_Q_COMPS 4 /* max components I can handle */
141
142 typedef struct {
143 struct jpeg_color_quantizer pub; /* public fields */
144
145 /* Initially allocated colormap is saved here */
146 JSAMPARRAY sv_colormap; /* The color map as a 2-D pixel array */
147 int sv_actual; /* number of entries in use */
148
149 JSAMPARRAY colorindex; /* Precomputed mapping for speed */
150 /* colorindex[i][j] = index of color closest to pixel value j in component i,
151 * premultiplied as described above. Since colormap indexes must fit into
152 * JSAMPLEs, the entries of this array will too.
153 */
154 boolean is_padded; /* is the colorindex padded for odither? */
155
156 int Ncolors[MAX_Q_COMPS]; /* # of values alloced to each component */
157
158 /* Variables for ordered dithering */
159 int row_index; /* cur row's vertical index in dither matrix */
160 ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */
161
162 /* Variables for Floyd-Steinberg dithering */
163 FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */
164 boolean on_odd_row; /* flag to remember which row we are on */
165 } my_cquantizer;
166
167 typedef my_cquantizer * my_cquantize_ptr;
168
169
170 /*
171 * Policy-making subroutines for create_colormap and create_colorindex.
172 * These routines determine the colormap to be used. The rest of the module
173 * only assumes that the colormap is orthogonal.
174 *
175 * * select_ncolors decides how to divvy up the available colors
176 * among the components.
177 * * output_value defines the set of representative values for a component.
178 * * largest_input_value defines the mapping from input values to
179 * representative values for a component.
180 * Note that the latter two routines may impose different policies for
181 * different components, though this is not currently done.
182 */
183
184
185 LOCAL(int)
186 select_ncolors (j_decompress_ptr cinfo, int Ncolors[])
187 /* Determine allocation of desired colors to components, */
188 /* and fill in Ncolors[] array to indicate choice. */
189 /* Return value is total number of colors (product of Ncolors[] values). */
190 {
191 int nc = cinfo->out_color_components; /* number of color components */
192 int max_colors = cinfo->desired_number_of_colors;
193 int total_colors, iroot, i, j;
194 boolean changed;
195 long temp;
196 static const int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE };
197
198 /* We can allocate at least the nc'th root of max_colors per component. */
199 /* Compute floor(nc'th root of max_colors). */
200 iroot = 1;
201 do {
202 iroot++;
203 temp = iroot; /* set temp = iroot ** nc */
204 for (i = 1; i < nc; i++)
205 temp *= iroot;
206 } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */
207 iroot--; /* now iroot = floor(root) */
208
209 /* Must have at least 2 color values per component */
210 if (iroot < 2)
211 ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp);
212
213 /* Initialize to iroot color values for each component */
214 total_colors = 1;
215 for (i = 0; i < nc; i++) {
216 Ncolors[i] = iroot;
217 total_colors *= iroot;
218 }
219 /* We may be able to increment the count for one or more components without
220 * exceeding max_colors, though we know not all can be incremented.
221 * Sometimes, the first component can be incremented more than once!
222 * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)
223 * In RGB colorspace, try to increment G first, then R, then B.
224 */
225 do {
226 changed = FALSE;
227 for (i = 0; i < nc; i++) {
228 j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i);
229 /* calculate new total_colors if Ncolors[j] is incremented */
230 temp = total_colors / Ncolors[j];
231 temp *= Ncolors[j]+1; /* done in long arith to avoid oflo */
232 if (temp > (long) max_colors)
233 break; /* won't fit, done with this pass */
234 Ncolors[j]++; /* OK, apply the increment */
235 total_colors = (int) temp;
236 changed = TRUE;
237 }
238 } while (changed);
239
240 return total_colors;
241 }
242
243
244 LOCAL(int)
245 output_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
246 /* Return j'th output value, where j will range from 0 to maxj */
247 /* The output values must fall in 0..MAXJSAMPLE in increasing order */
248 {
249 /* We always provide values 0 and MAXJSAMPLE for each component;
250 * any additional values are equally spaced between these limits.
251 * (Forcing the upper and lower values to the limits ensures that
252 * dithering can't produce a color outside the selected gamut.)
253 */
254 return (int) (((INT32) j * MAXJSAMPLE + maxj/2) / maxj);
255 }
256
257
258 LOCAL(int)
259 largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
260 /* Return largest input value that should map to j'th output value */
261 /* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */
262 {
263 /* Breakpoints are halfway between values returned by output_value */
264 return (int) (((INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj));
265 }
266
267
268 /*
269 * Create the colormap.
270 */
271
272 LOCAL(void)
273 create_colormap (j_decompress_ptr cinfo)
274 {
275 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
276 JSAMPARRAY colormap; /* Created colormap */
277 int total_colors; /* Number of distinct output colors */
278 int i,j,k, nci, blksize, blkdist, ptr, val;
279
280 /* Select number of colors for each component */
281 total_colors = select_ncolors(cinfo, cquantize->Ncolors);
282
283 /* Report selected color counts */
284 if (cinfo->out_color_components == 3)
285 TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS,
286 total_colors, cquantize->Ncolors[0],
287 cquantize->Ncolors[1], cquantize->Ncolors[2]);
288 else
289 TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors);
290
291 /* Allocate and fill in the colormap. */
292 /* The colors are ordered in the map in standard row-major order, */
293 /* i.e. rightmost (highest-indexed) color changes most rapidly. */
294
295 colormap = (*cinfo->mem->alloc_sarray)
296 ((j_common_ptr) cinfo, JPOOL_IMAGE,
297 (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components);
298
299 /* blksize is number of adjacent repeated entries for a component */
300 /* blkdist is distance between groups of identical entries for a component */
301 blkdist = total_colors;
302
303 for (i = 0; i < cinfo->out_color_components; i++) {
304 /* fill in colormap entries for i'th color component */
305 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
306 blksize = blkdist / nci;
307 for (j = 0; j < nci; j++) {
308 /* Compute j'th output value (out of nci) for component */
309 val = output_value(cinfo, i, j, nci-1);
310 /* Fill in all colormap entries that have this value of this component */
311 for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) {
312 /* fill in blksize entries beginning at ptr */
313 for (k = 0; k < blksize; k++)
314 colormap[i][ptr+k] = (JSAMPLE) val;
315 }
316 }
317 blkdist = blksize; /* blksize of this color is blkdist of next */
318 }
319
320 /* Save the colormap in private storage,
321 * where it will survive color quantization mode changes.
322 */
323 cquantize->sv_colormap = colormap;
324 cquantize->sv_actual = total_colors;
325 }
326
327
328 /*
329 * Create the color index table.
330 */
331
332 LOCAL(void)
333 create_colorindex (j_decompress_ptr cinfo)
334 {
335 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
336 JSAMPROW indexptr;
337 int i,j,k, nci, blksize, val, pad;
338
339 /* For ordered dither, we pad the color index tables by MAXJSAMPLE in
340 * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE).
341 * This is not necessary in the other dithering modes. However, we
342 * flag whether it was done in case user changes dithering mode.
343 */
344 if (cinfo->dither_mode == JDITHER_ORDERED) {
345 pad = MAXJSAMPLE*2;
346 cquantize->is_padded = TRUE;
347 } else {
348 pad = 0;
349 cquantize->is_padded = FALSE;
350 }
351
352 cquantize->colorindex = (*cinfo->mem->alloc_sarray)
353 ((j_common_ptr) cinfo, JPOOL_IMAGE,
354 (JDIMENSION) (MAXJSAMPLE+1 + pad),
355 (JDIMENSION) cinfo->out_color_components);
356
357 /* blksize is number of adjacent repeated entries for a component */
358 blksize = cquantize->sv_actual;
359
360 for (i = 0; i < cinfo->out_color_components; i++) {
361 /* fill in colorindex entries for i'th color component */
362 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
363 blksize = blksize / nci;
364
365 /* adjust colorindex pointers to provide padding at negative indexes. */
366 if (pad)
367 cquantize->colorindex[i] += MAXJSAMPLE;
368
369 /* in loop, val = index of current output value, */
370 /* and k = largest j that maps to current val */
371 indexptr = cquantize->colorindex[i];
372 val = 0;
373 k = largest_input_value(cinfo, i, 0, nci-1);
374 for (j = 0; j <= MAXJSAMPLE; j++) {
375 while (j > k) /* advance val if past boundary */
376 k = largest_input_value(cinfo, i, ++val, nci-1);
377 /* premultiply so that no multiplication needed in main processing */
378 indexptr[j] = (JSAMPLE) (val * blksize);
379 }
380 /* Pad at both ends if necessary */
381 if (pad)
382 for (j = 1; j <= MAXJSAMPLE; j++) {
383 indexptr[-j] = indexptr[0];
384 indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE];
385 }
386 }
387 }
388
389
390 /*
391 * Create an ordered-dither array for a component having ncolors
392 * distinct output values.
393 */
394
395 LOCAL(ODITHER_MATRIX_PTR)
396 make_odither_array (j_decompress_ptr cinfo, int ncolors)
397 {
398 ODITHER_MATRIX_PTR odither;
399 int j,k;
400 INT32 num,den;
401
402 odither = (ODITHER_MATRIX_PTR)
403 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
404 SIZEOF(ODITHER_MATRIX));
405 /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1).
406 * Hence the dither value for the matrix cell with fill order f
407 * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1).
408 * On 16-bit-int machine, be careful to avoid overflow.
409 */
410 den = 2 * ODITHER_CELLS * ((INT32) (ncolors - 1));
411 for (j = 0; j < ODITHER_SIZE; j++) {
412 for (k = 0; k < ODITHER_SIZE; k++) {
413 num = ((INT32) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k])))
414 * MAXJSAMPLE;
415 /* Ensure round towards zero despite C's lack of consistency
416 * about rounding negative values in integer division...
417 */
418 odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den);
419 }
420 }
421 return odither;
422 }
423
424
425 /*
426 * Create the ordered-dither tables.
427 * Components having the same number of representative colors may
428 * share a dither table.
429 */
430
431 LOCAL(void)
432 create_odither_tables (j_decompress_ptr cinfo)
433 {
434 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
435 ODITHER_MATRIX_PTR odither;
436 int i, j, nci;
437
438 for (i = 0; i < cinfo->out_color_components; i++) {
439 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
440 odither = NULL; /* search for matching prior component */
441 for (j = 0; j < i; j++) {
442 if (nci == cquantize->Ncolors[j]) {
443 odither = cquantize->odither[j];
444 break;
445 }
446 }
447 if (odither == NULL) /* need a new table? */
448 odither = make_odither_array(cinfo, nci);
449 cquantize->odither[i] = odither;
450 }
451 }
452
453
454 /*
455 * Map some rows of pixels to the output colormapped representation.
456 */
457
458 METHODDEF(void)
459 color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
460 JSAMPARRAY output_buf, int num_rows)
461 /* General case, no dithering */
462 {
463 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
464 JSAMPARRAY colorindex = cquantize->colorindex;
465 register int pixcode, ci;
466 register JSAMPROW ptrin, ptrout;
467 int row;
468 JDIMENSION col;
469 JDIMENSION width = cinfo->output_width;
470 register int nc = cinfo->out_color_components;
471
472 for (row = 0; row < num_rows; row++) {
473 ptrin = input_buf[row];
474 ptrout = output_buf[row];
475 for (col = width; col > 0; col--) {
476 pixcode = 0;
477 for (ci = 0; ci < nc; ci++) {
478 pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]);
479 }
480 *ptrout++ = (JSAMPLE) pixcode;
481 }
482 }
483 }
484
485
486 METHODDEF(void)
487 color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
488 JSAMPARRAY output_buf, int num_rows)
489 /* Fast path for out_color_components==3, no dithering */
490 {
491 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
492 register int pixcode;
493 register JSAMPROW ptrin, ptrout;
494 JSAMPROW colorindex0 = cquantize->colorindex[0];
495 JSAMPROW colorindex1 = cquantize->colorindex[1];
496 JSAMPROW colorindex2 = cquantize->colorindex[2];
497 int row;
498 JDIMENSION col;
499 JDIMENSION width = cinfo->output_width;
500
501 for (row = 0; row < num_rows; row++) {
502 ptrin = input_buf[row];
503 ptrout = output_buf[row];
504 for (col = width; col > 0; col--) {
505 pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]);
506 pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]);
507 pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]);
508 *ptrout++ = (JSAMPLE) pixcode;
509 }
510 }
511 }
512
513
514 METHODDEF(void)
515 quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
516 JSAMPARRAY output_buf, int num_rows)
517 /* General case, with ordered dithering */
518 {
519 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
520 register JSAMPROW input_ptr;
521 register JSAMPROW output_ptr;
522 JSAMPROW colorindex_ci;
523 int * dither; /* points to active row of dither matrix */
524 int row_index, col_index; /* current indexes into dither matrix */
525 int nc = cinfo->out_color_components;
526 int ci;
527 int row;
528 JDIMENSION col;
529 JDIMENSION width = cinfo->output_width;
530
531 for (row = 0; row < num_rows; row++) {
532 /* Initialize output values to 0 so can process components separately */
533 jzero_far((void FAR *) output_buf[row],
534 (size_t) (width * SIZEOF(JSAMPLE)));
535 row_index = cquantize->row_index;
536 for (ci = 0; ci < nc; ci++) {
537 input_ptr = input_buf[row] + ci;
538 output_ptr = output_buf[row];
539 colorindex_ci = cquantize->colorindex[ci];
540 dither = cquantize->odither[ci][row_index];
541 col_index = 0;
542
543 for (col = width; col > 0; col--) {
544 /* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,
545 * select output value, accumulate into output code for this pixel.
546 * Range-limiting need not be done explicitly, as we have extended
547 * the colorindex table to produce the right answers for out-of-range
548 * inputs. The maximum dither is +- MAXJSAMPLE; this sets the
549 * required amount of padding.
550 */
551 *output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]];
552 input_ptr += nc;
553 output_ptr++;
554 col_index = (col_index + 1) & ODITHER_MASK;
555 }
556 }
557 /* Advance row index for next row */
558 row_index = (row_index + 1) & ODITHER_MASK;
559 cquantize->row_index = row_index;
560 }
561 }
562
563
564 METHODDEF(void)
565 quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
566 JSAMPARRAY output_buf, int num_rows)
567 /* Fast path for out_color_components==3, with ordered dithering */
568 {
569 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
570 register int pixcode;
571 register JSAMPROW input_ptr;
572 register JSAMPROW output_ptr;
573 JSAMPROW colorindex0 = cquantize->colorindex[0];
574 JSAMPROW colorindex1 = cquantize->colorindex[1];
575 JSAMPROW colorindex2 = cquantize->colorindex[2];
576 int * dither0; /* points to active row of dither matrix */
577 int * dither1;
578 int * dither2;
579 int row_index, col_index; /* current indexes into dither matrix */
580 int row;
581 JDIMENSION col;
582 JDIMENSION width = cinfo->output_width;
583
584 for (row = 0; row < num_rows; row++) {
585 row_index = cquantize->row_index;
586 input_ptr = input_buf[row];
587 output_ptr = output_buf[row];
588 dither0 = cquantize->odither[0][row_index];
589 dither1 = cquantize->odither[1][row_index];
590 dither2 = cquantize->odither[2][row_index];
591 col_index = 0;
592
593 for (col = width; col > 0; col--) {
594 pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) +
595 dither0[col_index]]);
596 pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) +
597 dither1[col_index]]);
598 pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) +
599 dither2[col_index]]);
600 *output_ptr++ = (JSAMPLE) pixcode;
601 col_index = (col_index + 1) & ODITHER_MASK;
602 }
603 row_index = (row_index + 1) & ODITHER_MASK;
604 cquantize->row_index = row_index;
605 }
606 }
607
608
609 METHODDEF(void)
610 quantize_fs_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
611 JSAMPARRAY output_buf, int num_rows)
612 /* General case, with Floyd-Steinberg dithering */
613 {
614 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
615 register LOCFSERROR cur; /* current error or pixel value */
616 LOCFSERROR belowerr; /* error for pixel below cur */
617 LOCFSERROR bpreverr; /* error for below/prev col */
618 LOCFSERROR bnexterr; /* error for below/next col */
619 LOCFSERROR delta;
620 register FSERRPTR errorptr; /* => fserrors[] at column before current */
621 register JSAMPROW input_ptr;
622 register JSAMPROW output_ptr;
623 JSAMPROW colorindex_ci;
624 JSAMPROW colormap_ci;
625 int pixcode;
626 int nc = cinfo->out_color_components;
627 int dir; /* 1 for left-to-right, -1 for right-to-left */
628 int dirnc; /* dir * nc */
629 int ci;
630 int row;
631 JDIMENSION col;
632 JDIMENSION width = cinfo->output_width;
633 JSAMPLE *range_limit = cinfo->sample_range_limit;
634 SHIFT_TEMPS
635
636 for (row = 0; row < num_rows; row++) {
637 /* Initialize output values to 0 so can process components separately */
638 jzero_far((void FAR *) output_buf[row],
639 (size_t) (width * SIZEOF(JSAMPLE)));
640 for (ci = 0; ci < nc; ci++) {
641 input_ptr = input_buf[row] + ci;
642 output_ptr = output_buf[row];
643 if (cquantize->on_odd_row) {
644 /* work right to left in this row */
645 input_ptr += (width-1) * nc; /* so point to rightmost pixel */
646 output_ptr += width-1;
647 dir = -1;
648 dirnc = -nc;
649 errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */
650 } else {
651 /* work left to right in this row */
652 dir = 1;
653 dirnc = nc;
654 errorptr = cquantize->fserrors[ci]; /* => entry before first column */
655 }
656 colorindex_ci = cquantize->colorindex[ci];
657 colormap_ci = cquantize->sv_colormap[ci];
658 /* Preset error values: no error propagated to first pixel from left */
659 cur = 0;
660 /* and no error propagated to row below yet */
661 belowerr = bpreverr = 0;
662
663 for (col = width; col > 0; col--) {
664 /* cur holds the error propagated from the previous pixel on the
665 * current line. Add the error propagated from the previous line
666 * to form the complete error correction term for this pixel, and
667 * round the error term (which is expressed * 16) to an integer.
668 * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
669 * for either sign of the error value.
670 * Note: errorptr points to *previous* column's array entry.
671 */
672 cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4);
673 /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
674 * The maximum error is +- MAXJSAMPLE; this sets the required size
675 * of the range_limit array.
676 */
677 cur += GETJSAMPLE(*input_ptr);
678 cur = GETJSAMPLE(range_limit[cur]);
679 /* Select output value, accumulate into output code for this pixel */
680 pixcode = GETJSAMPLE(colorindex_ci[cur]);
681 *output_ptr += (JSAMPLE) pixcode;
682 /* Compute actual representation error at this pixel */
683 /* Note: we can do this even though we don't have the final */
684 /* pixel code, because the colormap is orthogonal. */
685 cur -= GETJSAMPLE(colormap_ci[pixcode]);
686 /* Compute error fractions to be propagated to adjacent pixels.
687 * Add these into the running sums, and simultaneously shift the
688 * next-line error sums left by 1 column.
689 */
690 bnexterr = cur;
691 delta = cur * 2;
692 cur += delta; /* form error * 3 */
693 errorptr[0] = (FSERROR) (bpreverr + cur);
694 cur += delta; /* form error * 5 */
695 bpreverr = belowerr + cur;
696 belowerr = bnexterr;
697 cur += delta; /* form error * 7 */
698 /* At this point cur contains the 7/16 error value to be propagated
699 * to the next pixel on the current line, and all the errors for the
700 * next line have been shifted over. We are therefore ready to move on.
701 */
702 input_ptr += dirnc; /* advance input ptr to next column */
703 output_ptr += dir; /* advance output ptr to next column */
704 errorptr += dir; /* advance errorptr to current column */
705 }
706 /* Post-loop cleanup: we must unload the final error value into the
707 * final fserrors[] entry. Note we need not unload belowerr because
708 * it is for the dummy column before or after the actual array.
709 */
710 errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */
711 }
712 cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);
713 }
714 }
715
716
717 /*
718 * Allocate workspace for Floyd-Steinberg errors.
719 */
720
721 LOCAL(void)
722 alloc_fs_workspace (j_decompress_ptr cinfo)
723 {
724 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
725 size_t arraysize;
726 int i;
727
728 arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
729 for (i = 0; i < cinfo->out_color_components; i++) {
730 cquantize->fserrors[i] = (FSERRPTR)
731 (*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize);
732 }
733 }
734
735
736 /*
737 * Initialize for one-pass color quantization.
738 */
739
740 METHODDEF(void)
741 start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan)
742 {
743 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
744 size_t arraysize;
745 int i;
746
747 /* Install my colormap. */
748 cinfo->colormap = cquantize->sv_colormap;
749 cinfo->actual_number_of_colors = cquantize->sv_actual;
750
751 /* Initialize for desired dithering mode. */
752 switch (cinfo->dither_mode) {
753 case JDITHER_NONE:
754 if (cinfo->out_color_components == 3)
755 cquantize->pub.color_quantize = color_quantize3;
756 else
757 cquantize->pub.color_quantize = color_quantize;
758 break;
759 case JDITHER_ORDERED:
760 if (cinfo->out_color_components == 3)
761 cquantize->pub.color_quantize = quantize3_ord_dither;
762 else
763 cquantize->pub.color_quantize = quantize_ord_dither;
764 cquantize->row_index = 0; /* initialize state for ordered dither */
765 /* If user changed to ordered dither from another mode,
766 * we must recreate the color index table with padding.
767 * This will cost extra space, but probably isn't very likely.
768 */
769 if (! cquantize->is_padded)
770 create_colorindex(cinfo);
771 /* Create ordered-dither tables if we didn't already. */
772 if (cquantize->odither[0] == NULL)
773 create_odither_tables(cinfo);
774 break;
775 case JDITHER_FS:
776 cquantize->pub.color_quantize = quantize_fs_dither;
777 cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */
778 /* Allocate Floyd-Steinberg workspace if didn't already. */
779 if (cquantize->fserrors[0] == NULL)
780 alloc_fs_workspace(cinfo);
781 /* Initialize the propagated errors to zero. */
782 arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
783 for (i = 0; i < cinfo->out_color_components; i++)
784 jzero_far((void FAR *) cquantize->fserrors[i], arraysize);
785 break;
786 default:
787 ERREXIT(cinfo, JERR_NOT_COMPILED);
788 break;
789 }
790 }
791
792
793 /*
794 * Finish up at the end of the pass.
795 */
796
797 METHODDEF(void)
798 finish_pass_1_quant (j_decompress_ptr cinfo)
799 {
800 /* no work in 1-pass case */
801 }
802
803
804 /*
805 * Switch to a new external colormap between output passes.
806 * Shouldn't get to this module!
807 */
808
809 METHODDEF(void)
810 new_color_map_1_quant (j_decompress_ptr cinfo)
811 {
812 ERREXIT(cinfo, JERR_MODE_CHANGE);
813 }
814
815
816 /*
817 * Module initialization routine for 1-pass color quantization.
818 */
819
820 GLOBAL(void)
821 jinit_1pass_quantizer (j_decompress_ptr cinfo)
822 {
823 my_cquantize_ptr cquantize;
824
825 cquantize = (my_cquantize_ptr)
826 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
827 SIZEOF(my_cquantizer));
828 cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;
829 cquantize->pub.start_pass = start_pass_1_quant;
830 cquantize->pub.finish_pass = finish_pass_1_quant;
831 cquantize->pub.new_color_map = new_color_map_1_quant;
832 cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */
833 cquantize->odither[0] = NULL; /* Also flag odither arrays not allocated */
834
835 /* Make sure my internal arrays won't overflow */
836 if (cinfo->out_color_components > MAX_Q_COMPS)
837 ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);
838 /* Make sure colormap indexes can be represented by JSAMPLEs */
839 if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))
840 ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1);
841
842 /* Create the colormap and color index table. */
843 create_colormap(cinfo);
844 create_colorindex(cinfo);
845
846 /* Allocate Floyd-Steinberg workspace now if requested.
847 * We do this now since it is FAR storage and may affect the memory
848 * manager's space calculations. If the user changes to FS dither
849 * mode in a later pass, we will allocate the space then, and will
850 * possibly overrun the max_memory_to_use setting.
851 */
852 if (cinfo->dither_mode == JDITHER_FS)
853 alloc_fs_workspace(cinfo);
854 }
855
856 #endif /* QUANT_1PASS_SUPPORTED */