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jdcolor.c (12962B)
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1 /*
2 * jdcolor.c
3 *
4 * Copyright (C) 1991-1997, 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 output 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_deconverter pub; /* public fields */
20
21 /* Private state for YCC->RGB conversion */
22 int * Cr_r_tab; /* => table for Cr to R conversion */
23 int * Cb_b_tab; /* => table for Cb to B conversion */
24 INT32 * Cr_g_tab; /* => table for Cr to G conversion */
25 INT32 * Cb_g_tab; /* => table for Cb to G conversion */
26 } my_color_deconverter;
27
28 typedef my_color_deconverter * my_cconvert_ptr;
29
30
31 /**************** YCbCr -> RGB conversion: most common case **************/
32
33 /*
34 * YCbCr is defined per CCIR 601-1, except that Cb and Cr are
35 * normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
36 * The conversion equations to be implemented are therefore
37 * R = Y + 1.40200 * Cr
38 * G = Y - 0.34414 * Cb - 0.71414 * Cr
39 * B = Y + 1.77200 * Cb
40 * where Cb and Cr represent the incoming values less CENTERJSAMPLE.
41 * (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
42 *
43 * To avoid floating-point arithmetic, we represent the fractional constants
44 * as integers scaled up by 2^16 (about 4 digits precision); we have to divide
45 * the products by 2^16, with appropriate rounding, to get the correct answer.
46 * Notice that Y, being an integral input, does not contribute any fraction
47 * so it need not participate in the rounding.
48 *
49 * For even more speed, we avoid doing any multiplications in the inner loop
50 * by precalculating the constants times Cb and Cr for all possible values.
51 * For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
52 * for 12-bit samples it is still acceptable. It's not very reasonable for
53 * 16-bit samples, but if you want lossless storage you shouldn't be changing
54 * colorspace anyway.
55 * The Cr=>R and Cb=>B values can be rounded to integers in advance; the
56 * values for the G calculation are left scaled up, since we must add them
57 * together before rounding.
58 */
59
60 #define SCALEBITS 16 /* speediest right-shift on some machines */
61 #define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
62 #define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
63
64
65 /*
66 * Initialize tables for YCC->RGB colorspace conversion.
67 */
68
69 LOCAL(void)
70 build_ycc_rgb_table (j_decompress_ptr cinfo)
71 {
72 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
73 int i;
74 INT32 x;
75 SHIFT_TEMPS
76
77 cconvert->Cr_r_tab = (int *)
78 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
79 (MAXJSAMPLE+1) * SIZEOF(int));
80 cconvert->Cb_b_tab = (int *)
81 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
82 (MAXJSAMPLE+1) * SIZEOF(int));
83 cconvert->Cr_g_tab = (INT32 *)
84 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
85 (MAXJSAMPLE+1) * SIZEOF(INT32));
86 cconvert->Cb_g_tab = (INT32 *)
87 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
88 (MAXJSAMPLE+1) * SIZEOF(INT32));
89
90 for (i = 0, x = -CENTERJSAMPLE; i <= MAXJSAMPLE; i++, x++) {
91 /* i is the actual input pixel value, in the range 0..MAXJSAMPLE */
92 /* The Cb or Cr value we are thinking of is x = i - CENTERJSAMPLE */
93 /* Cr=>R value is nearest int to 1.40200 * x */
94 cconvert->Cr_r_tab[i] = (int)
95 RIGHT_SHIFT(FIX(1.40200) * x + ONE_HALF, SCALEBITS);
96 /* Cb=>B value is nearest int to 1.77200 * x */
97 cconvert->Cb_b_tab[i] = (int)
98 RIGHT_SHIFT(FIX(1.77200) * x + ONE_HALF, SCALEBITS);
99 /* Cr=>G value is scaled-up -0.71414 * x */
100 cconvert->Cr_g_tab[i] = (- FIX(0.71414)) * x;
101 /* Cb=>G value is scaled-up -0.34414 * x */
102 /* We also add in ONE_HALF so that need not do it in inner loop */
103 cconvert->Cb_g_tab[i] = (- FIX(0.34414)) * x + ONE_HALF;
104 }
105 }
106
107
108 /*
109 * Convert some rows of samples to the output colorspace.
110 *
111 * Note that we change from noninterleaved, one-plane-per-component format
112 * to interleaved-pixel format. The output buffer is therefore three times
113 * as wide as the input buffer.
114 * A starting row offset is provided only for the input buffer. The caller
115 * can easily adjust the passed output_buf value to accommodate any row
116 * offset required on that side.
117 */
118
119 METHODDEF(void)
120 ycc_rgb_convert (j_decompress_ptr cinfo,
121 JSAMPIMAGE input_buf, JDIMENSION input_row,
122 JSAMPARRAY output_buf, int num_rows)
123 {
124 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
125 register int y, cb, cr;
126 register JSAMPROW outptr;
127 register JSAMPROW inptr0, inptr1, inptr2;
128 register JDIMENSION col;
129 JDIMENSION num_cols = cinfo->output_width;
130 /* copy these pointers into registers if possible */
131 register JSAMPLE * range_limit = cinfo->sample_range_limit;
132 register int * Crrtab = cconvert->Cr_r_tab;
133 register int * Cbbtab = cconvert->Cb_b_tab;
134 register INT32 * Crgtab = cconvert->Cr_g_tab;
135 register INT32 * Cbgtab = cconvert->Cb_g_tab;
136 SHIFT_TEMPS
137
138 while (--num_rows >= 0) {
139 inptr0 = input_buf[0][input_row];
140 inptr1 = input_buf[1][input_row];
141 inptr2 = input_buf[2][input_row];
142 input_row++;
143 outptr = *output_buf++;
144 for (col = 0; col < num_cols; col++) {
145 y = GETJSAMPLE(inptr0[col]);
146 cb = GETJSAMPLE(inptr1[col]);
147 cr = GETJSAMPLE(inptr2[col]);
148 /* Range-limiting is essential due to noise introduced by DCT losses. */
149 outptr[RGB_RED] = range_limit[y + Crrtab[cr]];
150 outptr[RGB_GREEN] = range_limit[y +
151 ((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
152 SCALEBITS))];
153 outptr[RGB_BLUE] = range_limit[y + Cbbtab[cb]];
154 outptr += RGB_PIXELSIZE;
155 }
156 }
157 }
158
159
160 /**************** Cases other than YCbCr -> RGB **************/
161
162
163 /*
164 * Color conversion for no colorspace change: just copy the data,
165 * converting from separate-planes to interleaved representation.
166 */
167
168 METHODDEF(void)
169 null_convert (j_decompress_ptr cinfo,
170 JSAMPIMAGE input_buf, JDIMENSION input_row,
171 JSAMPARRAY output_buf, int num_rows)
172 {
173 register JSAMPROW inptr, outptr;
174 register JDIMENSION count;
175 register int num_components = cinfo->num_components;
176 JDIMENSION num_cols = cinfo->output_width;
177 int ci;
178
179 while (--num_rows >= 0) {
180 for (ci = 0; ci < num_components; ci++) {
181 inptr = input_buf[ci][input_row];
182 outptr = output_buf[0] + ci;
183 for (count = num_cols; count > 0; count--) {
184 *outptr = *inptr++; /* needn't bother with GETJSAMPLE() here */
185 outptr += num_components;
186 }
187 }
188 input_row++;
189 output_buf++;
190 }
191 }
192
193
194 /*
195 * Color conversion for grayscale: just copy the data.
196 * This also works for YCbCr -> grayscale conversion, in which
197 * we just copy the Y (luminance) component and ignore chrominance.
198 */
199
200 METHODDEF(void)
201 grayscale_convert (j_decompress_ptr cinfo,
202 JSAMPIMAGE input_buf, JDIMENSION input_row,
203 JSAMPARRAY output_buf, int num_rows)
204 {
205 jcopy_sample_rows(input_buf[0], (int) input_row, output_buf, 0,
206 num_rows, cinfo->output_width);
207 }
208
209
210 /*
211 * Convert grayscale to RGB: just duplicate the graylevel three times.
212 * This is provided to support applications that don't want to cope
213 * with grayscale as a separate case.
214 */
215
216 METHODDEF(void)
217 gray_rgb_convert (j_decompress_ptr cinfo,
218 JSAMPIMAGE input_buf, JDIMENSION input_row,
219 JSAMPARRAY output_buf, int num_rows)
220 {
221 register JSAMPROW inptr, outptr;
222 register JDIMENSION col;
223 JDIMENSION num_cols = cinfo->output_width;
224
225 while (--num_rows >= 0) {
226 inptr = input_buf[0][input_row++];
227 outptr = *output_buf++;
228 for (col = 0; col < num_cols; col++) {
229 /* We can dispense with GETJSAMPLE() here */
230 outptr[RGB_RED] = outptr[RGB_GREEN] = outptr[RGB_BLUE] = inptr[col];
231 outptr += RGB_PIXELSIZE;
232 }
233 }
234 }
235
236
237 /*
238 * Adobe-style YCCK->CMYK conversion.
239 * We convert YCbCr to R=1-C, G=1-M, and B=1-Y using the same
240 * conversion as above, while passing K (black) unchanged.
241 * We assume build_ycc_rgb_table has been called.
242 */
243
244 METHODDEF(void)
245 ycck_cmyk_convert (j_decompress_ptr cinfo,
246 JSAMPIMAGE input_buf, JDIMENSION input_row,
247 JSAMPARRAY output_buf, int num_rows)
248 {
249 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
250 register int y, cb, cr;
251 register JSAMPROW outptr;
252 register JSAMPROW inptr0, inptr1, inptr2, inptr3;
253 register JDIMENSION col;
254 JDIMENSION num_cols = cinfo->output_width;
255 /* copy these pointers into registers if possible */
256 register JSAMPLE * range_limit = cinfo->sample_range_limit;
257 register int * Crrtab = cconvert->Cr_r_tab;
258 register int * Cbbtab = cconvert->Cb_b_tab;
259 register INT32 * Crgtab = cconvert->Cr_g_tab;
260 register INT32 * Cbgtab = cconvert->Cb_g_tab;
261 SHIFT_TEMPS
262
263 while (--num_rows >= 0) {
264 inptr0 = input_buf[0][input_row];
265 inptr1 = input_buf[1][input_row];
266 inptr2 = input_buf[2][input_row];
267 inptr3 = input_buf[3][input_row];
268 input_row++;
269 outptr = *output_buf++;
270 for (col = 0; col < num_cols; col++) {
271 y = GETJSAMPLE(inptr0[col]);
272 cb = GETJSAMPLE(inptr1[col]);
273 cr = GETJSAMPLE(inptr2[col]);
274 /* Range-limiting is essential due to noise introduced by DCT losses. */
275 outptr[0] = range_limit[MAXJSAMPLE - (y + Crrtab[cr])]; /* red */
276 outptr[1] = range_limit[MAXJSAMPLE - (y + /* green */
277 ((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
278 SCALEBITS)))];
279 outptr[2] = range_limit[MAXJSAMPLE - (y + Cbbtab[cb])]; /* blue */
280 /* K passes through unchanged */
281 outptr[3] = inptr3[col]; /* don't need GETJSAMPLE here */
282 outptr += 4;
283 }
284 }
285 }
286
287
288 /*
289 * Empty method for start_pass.
290 */
291
292 METHODDEF(void)
293 start_pass_dcolor (j_decompress_ptr cinfo)
294 {
295 /* no work needed */
296 }
297
298
299 /*
300 * Module initialization routine for output colorspace conversion.
301 */
302
303 GLOBAL(void)
304 jinit_color_deconverter (j_decompress_ptr cinfo)
305 {
306 my_cconvert_ptr cconvert;
307 int ci;
308
309 cconvert = (my_cconvert_ptr)
310 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
311 SIZEOF(my_color_deconverter));
312 cinfo->cconvert = (struct jpeg_color_deconverter *) cconvert;
313 cconvert->pub.start_pass = start_pass_dcolor;
314
315 /* Make sure num_components agrees with jpeg_color_space */
316 switch (cinfo->jpeg_color_space) {
317 case JCS_GRAYSCALE:
318 if (cinfo->num_components != 1)
319 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
320 break;
321
322 case JCS_RGB:
323 case JCS_YCbCr:
324 if (cinfo->num_components != 3)
325 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
326 break;
327
328 case JCS_CMYK:
329 case JCS_YCCK:
330 if (cinfo->num_components != 4)
331 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
332 break;
333
334 default: /* JCS_UNKNOWN can be anything */
335 if (cinfo->num_components < 1)
336 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
337 break;
338 }
339
340 /* Set out_color_components and conversion method based on requested space.
341 * Also clear the component_needed flags for any unused components,
342 * so that earlier pipeline stages can avoid useless computation.
343 */
344
345 switch (cinfo->out_color_space) {
346 case JCS_GRAYSCALE:
347 cinfo->out_color_components = 1;
348 if (cinfo->jpeg_color_space == JCS_GRAYSCALE ||
349 cinfo->jpeg_color_space == JCS_YCbCr) {
350 cconvert->pub.color_convert = grayscale_convert;
351 /* For color->grayscale conversion, only the Y (0) component is needed */
352 for (ci = 1; ci < cinfo->num_components; ci++)
353 cinfo->comp_info[ci].component_needed = FALSE;
354 } else
355 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
356 break;
357
358 case JCS_RGB:
359 cinfo->out_color_components = RGB_PIXELSIZE;
360 if (cinfo->jpeg_color_space == JCS_YCbCr) {
361 cconvert->pub.color_convert = ycc_rgb_convert;
362 build_ycc_rgb_table(cinfo);
363 } else if (cinfo->jpeg_color_space == JCS_GRAYSCALE) {
364 cconvert->pub.color_convert = gray_rgb_convert;
365 } else if (cinfo->jpeg_color_space == JCS_RGB && RGB_PIXELSIZE == 3) {
366 cconvert->pub.color_convert = null_convert;
367 } else
368 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
369 break;
370
371 case JCS_CMYK:
372 cinfo->out_color_components = 4;
373 if (cinfo->jpeg_color_space == JCS_YCCK) {
374 cconvert->pub.color_convert = ycck_cmyk_convert;
375 build_ycc_rgb_table(cinfo);
376 } else if (cinfo->jpeg_color_space == JCS_CMYK) {
377 cconvert->pub.color_convert = null_convert;
378 } else
379 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
380 break;
381
382 default:
383 /* Permit null conversion to same output space */
384 if (cinfo->out_color_space == cinfo->jpeg_color_space) {
385 cinfo->out_color_components = cinfo->num_components;
386 cconvert->pub.color_convert = null_convert;
387 } else /* unsupported non-null conversion */
388 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
389 break;
390 }
391
392 if (cinfo->quantize_colors)
393 cinfo->output_components = 1; /* single colormapped output component */
394 else
395 cinfo->output_components = cinfo->out_color_components;
396 }