1 /*
2 * jccolor.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 input colorspace conversion routines.
9 */
10
11 #define JPEG_INTERNALS
12 #include "jinclude.h"
13 #include "jpeglib.h"
14
15
16 /* Private subobject */
17
18 typedef struct {
19 struct jpeg_color_converter pub; /* public fields */
20
21 /* Private state for RGB->YCC conversion */
22 INT32 * rgb_ycc_tab; /* => table for RGB to YCbCr conversion */
23 } my_color_converter;
24
25 typedef my_color_converter * my_cconvert_ptr;
26
27
28 /**************** RGB -> YCbCr conversion: most common case **************/
29
30 /*
31 * YCbCr is defined per CCIR 601-1, except that Cb and Cr are
32 * normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
33 * The conversion equations to be implemented are therefore
34 * Y = 0.29900 * R + 0.58700 * G + 0.11400 * B
35 * Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B + CENTERJSAMPLE
36 * Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B + CENTERJSAMPLE
37 * (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
38 * Note: older versions of the IJG code used a zero offset of MAXJSAMPLE/2,
39 * rather than CENTERJSAMPLE, for Cb and Cr. This gave equal positive and
40 * negative swings for Cb/Cr, but meant that grayscale values (Cb=Cr=0)
41 * were not represented exactly. Now we sacrifice exact representation of
42 * maximum red and maximum blue in order to get exact grayscales.
43 *
44 * To avoid floating-point arithmetic, we represent the fractional constants
45 * as integers scaled up by 2^16 (about 4 digits precision); we have to divide
46 * the products by 2^16, with appropriate rounding, to get the correct answer.
47 *
48 * For even more speed, we avoid doing any multiplications in the inner loop
49 * by precalculating the constants times R,G,B for all possible values.
50 * For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
51 * for 12-bit samples it is still acceptable. It's not very reasonable for
52 * 16-bit samples, but if you want lossless storage you shouldn't be changing
53 * colorspace anyway.
54 * The CENTERJSAMPLE offsets and the rounding fudge-factor of 0.5 are included
55 * in the tables to save adding them separately in the inner loop.
56 */
57
58 #define SCALEBITS 16 /* speediest right-shift on some machines */
59 #define CBCR_OFFSET ((INT32) CENTERJSAMPLE << SCALEBITS)
60 #define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
61 #define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
62
63 /* We allocate one big table and divide it up into eight parts, instead of
64 * doing eight alloc_small requests. This lets us use a single table base
65 * address, which can be held in a register in the inner loops on many
66 * machines (more than can hold all eight addresses, anyway).
67 */
68
69 #define R_Y_OFF 0 /* offset to R => Y section */
70 #define G_Y_OFF (1*(MAXJSAMPLE+1)) /* offset to G => Y section */
71 #define B_Y_OFF (2*(MAXJSAMPLE+1)) /* etc. */
72 #define R_CB_OFF (3*(MAXJSAMPLE+1))
73 #define G_CB_OFF (4*(MAXJSAMPLE+1))
74 #define B_CB_OFF (5*(MAXJSAMPLE+1))
75 #define R_CR_OFF B_CB_OFF /* B=>Cb, R=>Cr are the same */
76 #define G_CR_OFF (6*(MAXJSAMPLE+1))
77 #define B_CR_OFF (7*(MAXJSAMPLE+1))
78 #define TABLE_SIZE (8*(MAXJSAMPLE+1))
79
80
81 /*
82 * Initialize for RGB->YCC colorspace conversion.
83 */
84
85 METHODDEF(void)
86 rgb_ycc_start (j_compress_ptr cinfo)
87 {
88 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
89 INT32 * rgb_ycc_tab;
90 INT32 i;
91
92 /* Allocate and fill in the conversion tables. */
93 cconvert->rgb_ycc_tab = rgb_ycc_tab = (INT32 *)
94 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
95 (TABLE_SIZE * SIZEOF(INT32)));
96
97 for (i = 0; i <= MAXJSAMPLE; i++) {
98 rgb_ycc_tab[i+R_Y_OFF] = FIX(0.29900) * i;
99 rgb_ycc_tab[i+G_Y_OFF] = FIX(0.58700) * i;
100 rgb_ycc_tab[i+B_Y_OFF] = FIX(0.11400) * i + ONE_HALF;
101 rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.16874)) * i;
102 rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.33126)) * i;
103 /* We use a rounding fudge-factor of 0.5-epsilon for Cb and Cr.
104 * This ensures that the maximum output will round to MAXJSAMPLE
105 * not MAXJSAMPLE+1, and thus that we don't have to range-limit.
106 */
107 rgb_ycc_tab[i+B_CB_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
108 /* B=>Cb and R=>Cr tables are the same
109 rgb_ycc_tab[i+R_CR_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
110 */
111 rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.41869)) * i;
112 rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.08131)) * i;
113 }
114 }
115
116
117 /*
118 * Convert some rows of samples to the JPEG colorspace.
119 *
120 * Note that we change from the application's interleaved-pixel format
121 * to our internal noninterleaved, one-plane-per-component format.
122 * The input buffer is therefore three times as wide as the output buffer.
123 *
124 * A starting row offset is provided only for the output buffer. The caller
125 * can easily adjust the passed input_buf value to accommodate any row
126 * offset required on that side.
127 */
128
129 METHODDEF(void)
130 rgb_ycc_convert (j_compress_ptr cinfo,
131 JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
132 JDIMENSION output_row, int num_rows)
133 {
134 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
135 register int r, g, b;
136 register INT32 * ctab = cconvert->rgb_ycc_tab;
137 register JSAMPROW inptr;
138 register JSAMPROW outptr0, outptr1, outptr2;
139 register JDIMENSION col;
140 JDIMENSION num_cols = cinfo->image_width;
141
142 while (--num_rows >= 0) {
143 inptr = *input_buf++;
144 outptr0 = output_buf[0][output_row];
145 outptr1 = output_buf[1][output_row];
146 outptr2 = output_buf[2][output_row];
147 output_row++;
148 for (col = 0; col < num_cols; col++) {
149 r = GETJSAMPLE(inptr[RGB_RED]);
150 g = GETJSAMPLE(inptr[RGB_GREEN]);
151 b = GETJSAMPLE(inptr[RGB_BLUE]);
152 inptr += RGB_PIXELSIZE;
153 /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
154 * must be too; we do not need an explicit range-limiting operation.
155 * Hence the value being shifted is never negative, and we don't
156 * need the general RIGHT_SHIFT macro.
157 */
158 /* Y */
159 outptr0[col] = (JSAMPLE)
160 ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
161 >> SCALEBITS);
162 /* Cb */
163 outptr1[col] = (JSAMPLE)
164 ((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
165 >> SCALEBITS);
166 /* Cr */
167 outptr2[col] = (JSAMPLE)
168 ((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
169 >> SCALEBITS);
170 }
171 }
172 }
173
174
175 /**************** Cases other than RGB -> YCbCr **************/
176
177
178 /*
179 * Convert some rows of samples to the JPEG colorspace.
180 * This version handles RGB->grayscale conversion, which is the same
181 * as the RGB->Y portion of RGB->YCbCr.
182 * We assume rgb_ycc_start has been called (we only use the Y tables).
183 */
184
185 METHODDEF(void)
186 rgb_gray_convert (j_compress_ptr cinfo,
187 JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
188 JDIMENSION output_row, int num_rows)
189 {
190 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
191 register int r, g, b;
192 register INT32 * ctab = cconvert->rgb_ycc_tab;
193 register JSAMPROW inptr;
194 register JSAMPROW outptr;
195 register JDIMENSION col;
196 JDIMENSION num_cols = cinfo->image_width;
197
198 while (--num_rows >= 0) {
199 inptr = *input_buf++;
200 outptr = output_buf[0][output_row];
201 output_row++;
202 for (col = 0; col < num_cols; col++) {
203 r = GETJSAMPLE(inptr[RGB_RED]);
204 g = GETJSAMPLE(inptr[RGB_GREEN]);
205 b = GETJSAMPLE(inptr[RGB_BLUE]);
206 inptr += RGB_PIXELSIZE;
207 /* Y */
208 outptr[col] = (JSAMPLE)
209 ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
210 >> SCALEBITS);
211 }
212 }
213 }
214
215
216 /*
217 * Convert some rows of samples to the JPEG colorspace.
218 * This version handles Adobe-style CMYK->YCCK conversion,
219 * where we convert R=1-C, G=1-M, and B=1-Y to YCbCr using the same
220 * conversion as above, while passing K (black) unchanged.
221 * We assume rgb_ycc_start has been called.
222 */
223
224 METHODDEF(void)
225 cmyk_ycck_convert (j_compress_ptr cinfo,
226 JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
227 JDIMENSION output_row, int num_rows)
228 {
229 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
230 register int r, g, b;
231 register INT32 * ctab = cconvert->rgb_ycc_tab;
232 register JSAMPROW inptr;
233 register JSAMPROW outptr0, outptr1, outptr2, outptr3;
234 register JDIMENSION col;
235 JDIMENSION num_cols = cinfo->image_width;
236
237 while (--num_rows >= 0) {
238 inptr = *input_buf++;
239 outptr0 = output_buf[0][output_row];
240 outptr1 = output_buf[1][output_row];
241 outptr2 = output_buf[2][output_row];
242 outptr3 = output_buf[3][output_row];
243 output_row++;
244 for (col = 0; col < num_cols; col++) {
245 r = MAXJSAMPLE - GETJSAMPLE(inptr[0]);
246 g = MAXJSAMPLE - GETJSAMPLE(inptr[1]);
247 b = MAXJSAMPLE - GETJSAMPLE(inptr[2]);
248 /* K passes through as-is */
249 outptr3[col] = inptr[3]; /* don't need GETJSAMPLE here */
250 inptr += 4;
251 /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
252 * must be too; we do not need an explicit range-limiting operation.
253 * Hence the value being shifted is never negative, and we don't
254 * need the general RIGHT_SHIFT macro.
255 */
256 /* Y */
257 outptr0[col] = (JSAMPLE)
258 ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
259 >> SCALEBITS);
260 /* Cb */
261 outptr1[col] = (JSAMPLE)
262 ((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
263 >> SCALEBITS);
264 /* Cr */
265 outptr2[col] = (JSAMPLE)
266 ((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
267 >> SCALEBITS);
268 }
269 }
270 }
271
272
273 /*
274 * Convert some rows of samples to the JPEG colorspace.
275 * This version handles grayscale output with no conversion.
276 * The source can be either plain grayscale or YCbCr (since Y == gray).
277 */
278
279 METHODDEF(void)
280 grayscale_convert (j_compress_ptr cinfo,
281 JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
282 JDIMENSION output_row, int num_rows)
283 {
284 register JSAMPROW inptr;
285 register JSAMPROW outptr;
286 register JDIMENSION col;
287 JDIMENSION num_cols = cinfo->image_width;
288 int instride = cinfo->input_components;
289
290 while (--num_rows >= 0) {
291 inptr = *input_buf++;
292 outptr = output_buf[0][output_row];
293 output_row++;
294 for (col = 0; col < num_cols; col++) {
295 outptr[col] = inptr[0]; /* don't need GETJSAMPLE() here */
296 inptr += instride;
297 }
298 }
299 }
300
301
302 /*
303 * Convert some rows of samples to the JPEG colorspace.
304 * This version handles multi-component colorspaces without conversion.
305 * We assume input_components == num_components.
306 */
307
308 METHODDEF(void)
309 null_convert (j_compress_ptr cinfo,
310 JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
311 JDIMENSION output_row, int num_rows)
312 {
313 register JSAMPROW inptr;
314 register JSAMPROW outptr;
315 register JDIMENSION col;
316 register int ci;
317 int nc = cinfo->num_components;
318 JDIMENSION num_cols = cinfo->image_width;
319
320 while (--num_rows >= 0) {
321 /* It seems fastest to make a separate pass for each component. */
322 for (ci = 0; ci < nc; ci++) {
323 inptr = *input_buf;
324 outptr = output_buf[ci][output_row];
325 for (col = 0; col < num_cols; col++) {
326 outptr[col] = inptr[ci]; /* don't need GETJSAMPLE() here */
327 inptr += nc;
328 }
329 }
330 input_buf++;
331 output_row++;
332 }
333 }
334
335
336 /*
337 * Empty method for start_pass.
338 */
339
340 METHODDEF(void)
341 null_method (j_compress_ptr cinfo)
342 {
343 /* no work needed */
344 }
345
346
347 /*
348 * Module initialization routine for input colorspace conversion.
349 */
350
351 GLOBAL(void)
352 jinit_color_converter (j_compress_ptr cinfo)
353 {
354 my_cconvert_ptr cconvert;
355
356 cconvert = (my_cconvert_ptr)
357 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
358 SIZEOF(my_color_converter));
359 cinfo->cconvert = (struct jpeg_color_converter *) cconvert;
360 /* set start_pass to null method until we find out differently */
361 cconvert->pub.start_pass = null_method;
362
363 /* Make sure input_components agrees with in_color_space */
364 switch (cinfo->in_color_space) {
365 case JCS_GRAYSCALE:
366 if (cinfo->input_components != 1)
367 ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
368 break;
369
370 case JCS_RGB:
371 #if RGB_PIXELSIZE != 3
372 if (cinfo->input_components != RGB_PIXELSIZE)
373 ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
374 break;
375 #endif /* else share code with YCbCr */
376
377 case JCS_YCbCr:
378 if (cinfo->input_components != 3)
379 ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
380 break;
381
382 case JCS_CMYK:
383 case JCS_YCCK:
384 if (cinfo->input_components != 4)
385 ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
386 break;
387
388 default: /* JCS_UNKNOWN can be anything */
389 if (cinfo->input_components < 1)
390 ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
391 break;
392 }
393
394 /* Check num_components, set conversion method based on requested space */
395 switch (cinfo->jpeg_color_space) {
396 case JCS_GRAYSCALE:
397 if (cinfo->num_components != 1)
398 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
399 if (cinfo->in_color_space == JCS_GRAYSCALE)
400 cconvert->pub.color_convert = grayscale_convert;
401 else if (cinfo->in_color_space == JCS_RGB) {
402 cconvert->pub.start_pass = rgb_ycc_start;
403 cconvert->pub.color_convert = rgb_gray_convert;
404 } else if (cinfo->in_color_space == JCS_YCbCr)
405 cconvert->pub.color_convert = grayscale_convert;
406 else
407 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
408 break;
409
410 case JCS_RGB:
411 if (cinfo->num_components != 3)
412 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
413 if (cinfo->in_color_space == JCS_RGB && RGB_PIXELSIZE == 3)
414 cconvert->pub.color_convert = null_convert;
415 else
416 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
417 break;
418
419 case JCS_YCbCr:
420 if (cinfo->num_components != 3)
421 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
422 if (cinfo->in_color_space == JCS_RGB) {
423 cconvert->pub.start_pass = rgb_ycc_start;
424 cconvert->pub.color_convert = rgb_ycc_convert;
425 } else if (cinfo->in_color_space == JCS_YCbCr)
426 cconvert->pub.color_convert = null_convert;
427 else
428 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
429 break;
430
431 case JCS_CMYK:
432 if (cinfo->num_components != 4)
433 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
434 if (cinfo->in_color_space == JCS_CMYK)
435 cconvert->pub.color_convert = null_convert;
436 else
437 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
438 break;
439
440 case JCS_YCCK:
441 if (cinfo->num_components != 4)
442 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
443 if (cinfo->in_color_space == JCS_CMYK) {
444 cconvert->pub.start_pass = rgb_ycc_start;
445 cconvert->pub.color_convert = cmyk_ycck_convert;
446 } else if (cinfo->in_color_space == JCS_YCCK)
447 cconvert->pub.color_convert = null_convert;
448 else
449 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
450 break;
451
452 default: /* allow null conversion of JCS_UNKNOWN */
453 if (cinfo->jpeg_color_space != cinfo->in_color_space ||
454 cinfo->num_components != cinfo->input_components)
455 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
456 cconvert->pub.color_convert = null_convert;
457 break;
458 }
459 }