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.
8 * This file contains output colorspace conversion routines.
11 #define JPEG_INTERNALS
16 /* Private subobject */
19 struct jpeg_color_deconverter pub; /* public fields */
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;
28 typedef my_color_deconverter * my_cconvert_ptr;
31 /**************** YCbCr -> RGB conversion: most common case **************/
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.)
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.
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
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.
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))
66 * Initialize tables for YCC->RGB colorspace conversion.
70 build_ycc_rgb_table (j_decompress_ptr cinfo)
72 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
75 #if BITS_IN_JSAMPLE == 16
76 /* no need for temporaries */
81 cconvert->Cr_r_tab = (int *)
82 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
83 (MAXJSAMPLE+1) * SIZEOF(int));
84 cconvert->Cb_b_tab = (int *)
85 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
86 (MAXJSAMPLE+1) * SIZEOF(int));
87 cconvert->Cr_g_tab = (INT32 *)
88 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
89 (MAXJSAMPLE+1) * SIZEOF(INT32));
90 cconvert->Cb_g_tab = (INT32 *)
91 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
92 (MAXJSAMPLE+1) * SIZEOF(INT32));
94 for (i = 0, x = -CENTERJSAMPLE; i <= MAXJSAMPLE; i++, x++) {
95 /* i is the actual input pixel value, in the range 0..MAXJSAMPLE */
96 /* The Cb or Cr value we are thinking of is x = i - CENTERJSAMPLE */
98 #if BITS_IN_JSAMPLE == 16
99 /* Bug fix 2001-11-06 by Eichelberg: The integer routines below
100 produce an overflow when used with MAXJSAMPLE == 65535.
101 Use floating point calculation instead. */
103 /* Cr=>R value is nearest int to 1.40200 * x */
104 cconvert->Cr_r_tab[i] = (int)(1.40200 * (double)x + 0.5);
105 /* Cb=>B value is nearest int to 1.77200 * x */
106 cconvert->Cb_b_tab[i] = (int)(1.77200 * (double)x + 0.5);
108 /* Cr=>R value is nearest int to 1.40200 * x */
109 cconvert->Cr_r_tab[i] = (int)
110 RIGHT_SHIFT(FIX(1.40200) * x + ONE_HALF, SCALEBITS);
111 /* Cb=>B value is nearest int to 1.77200 * x */
112 cconvert->Cb_b_tab[i] = (int)
113 RIGHT_SHIFT(FIX(1.77200) * x + ONE_HALF, SCALEBITS);
116 /* Cr=>G value is scaled-up -0.71414 * x */
117 cconvert->Cr_g_tab[i] = (- FIX(0.71414)) * x;
118 /* Cb=>G value is scaled-up -0.34414 * x */
119 /* We also add in ONE_HALF so that need not do it in inner loop */
120 cconvert->Cb_g_tab[i] = (- FIX(0.34414)) * x + ONE_HALF;
126 * Convert some rows of samples to the output colorspace.
128 * Note that we change from noninterleaved, one-plane-per-component format
129 * to interleaved-pixel format. The output buffer is therefore three times
130 * as wide as the input buffer.
131 * A starting row offset is provided only for the input buffer. The caller
132 * can easily adjust the passed output_buf value to accommodate any row
133 * offset required on that side.
137 ycc_rgb_convert (j_decompress_ptr cinfo,
138 JSAMPIMAGE input_buf, JDIMENSION input_row,
139 JSAMPARRAY output_buf, int num_rows)
141 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
142 register int y, cb, cr;
143 register JSAMPROW outptr;
144 register JSAMPROW inptr0, inptr1, inptr2;
145 register JDIMENSION col;
146 JDIMENSION num_cols = cinfo->output_width;
147 /* copy these pointers into registers if possible */
148 register JSAMPLE * range_limit = cinfo->sample_range_limit;
149 register int * Crrtab = cconvert->Cr_r_tab;
150 register int * Cbbtab = cconvert->Cb_b_tab;
151 register INT32 * Crgtab = cconvert->Cr_g_tab;
152 register INT32 * Cbgtab = cconvert->Cb_g_tab;
155 while (--num_rows >= 0) {
156 inptr0 = input_buf[0][input_row];
157 inptr1 = input_buf[1][input_row];
158 inptr2 = input_buf[2][input_row];
160 outptr = *output_buf++;
161 for (col = 0; col < num_cols; col++) {
162 y = GETJSAMPLE(inptr0[col]);
163 cb = GETJSAMPLE(inptr1[col]);
164 cr = GETJSAMPLE(inptr2[col]);
165 /* Range-limiting is essential due to noise introduced by DCT losses. */
166 outptr[RGB_RED] = range_limit[y + Crrtab[cr]];
167 outptr[RGB_GREEN] = range_limit[y +
168 ((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
170 outptr[RGB_BLUE] = range_limit[y + Cbbtab[cb]];
171 outptr += RGB_PIXELSIZE;
177 /**************** Cases other than YCbCr -> RGB **************/
181 * Color conversion for no colorspace change: just copy the data,
182 * converting from separate-planes to interleaved representation.
186 null_convert (j_decompress_ptr cinfo,
187 JSAMPIMAGE input_buf, JDIMENSION input_row,
188 JSAMPARRAY output_buf, int num_rows)
190 register JSAMPROW inptr, outptr;
191 register JDIMENSION count;
192 register int num_components = cinfo->num_components;
193 JDIMENSION num_cols = cinfo->output_width;
196 while (--num_rows >= 0) {
197 for (ci = 0; ci < num_components; ci++) {
198 inptr = input_buf[ci][input_row];
199 outptr = output_buf[0] + ci;
200 for (count = num_cols; count > 0; count--) {
201 *outptr = *inptr++; /* needn't bother with GETJSAMPLE() here */
202 outptr += num_components;
212 * Color conversion for grayscale: just copy the data.
213 * This also works for YCbCr -> grayscale conversion, in which
214 * we just copy the Y (luminance) component and ignore chrominance.
218 grayscale_convert (j_decompress_ptr cinfo,
219 JSAMPIMAGE input_buf, JDIMENSION input_row,
220 JSAMPARRAY output_buf, int num_rows)
222 jcopy_sample_rows(input_buf[0], (int) input_row, output_buf, 0,
223 num_rows, cinfo->output_width);
228 * Convert grayscale to RGB: just duplicate the graylevel three times.
229 * This is provided to support applications that don't want to cope
230 * with grayscale as a separate case.
234 gray_rgb_convert (j_decompress_ptr cinfo,
235 JSAMPIMAGE input_buf, JDIMENSION input_row,
236 JSAMPARRAY output_buf, int num_rows)
238 register JSAMPROW inptr, outptr;
239 register JDIMENSION col;
240 JDIMENSION num_cols = cinfo->output_width;
242 while (--num_rows >= 0) {
243 inptr = input_buf[0][input_row++];
244 outptr = *output_buf++;
245 for (col = 0; col < num_cols; col++) {
246 /* We can dispense with GETJSAMPLE() here */
247 outptr[RGB_RED] = outptr[RGB_GREEN] = outptr[RGB_BLUE] = inptr[col];
248 outptr += RGB_PIXELSIZE;
255 * Adobe-style YCCK->CMYK conversion.
256 * We convert YCbCr to R=1-C, G=1-M, and B=1-Y using the same
257 * conversion as above, while passing K (black) unchanged.
258 * We assume build_ycc_rgb_table has been called.
262 ycck_cmyk_convert (j_decompress_ptr cinfo,
263 JSAMPIMAGE input_buf, JDIMENSION input_row,
264 JSAMPARRAY output_buf, int num_rows)
266 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
267 register int y, cb, cr;
268 register JSAMPROW outptr;
269 register JSAMPROW inptr0, inptr1, inptr2, inptr3;
270 register JDIMENSION col;
271 JDIMENSION num_cols = cinfo->output_width;
272 /* copy these pointers into registers if possible */
273 register JSAMPLE * range_limit = cinfo->sample_range_limit;
274 register int * Crrtab = cconvert->Cr_r_tab;
275 register int * Cbbtab = cconvert->Cb_b_tab;
276 register INT32 * Crgtab = cconvert->Cr_g_tab;
277 register INT32 * Cbgtab = cconvert->Cb_g_tab;
280 while (--num_rows >= 0) {
281 inptr0 = input_buf[0][input_row];
282 inptr1 = input_buf[1][input_row];
283 inptr2 = input_buf[2][input_row];
284 inptr3 = input_buf[3][input_row];
286 outptr = *output_buf++;
287 for (col = 0; col < num_cols; col++) {
288 y = GETJSAMPLE(inptr0[col]);
289 cb = GETJSAMPLE(inptr1[col]);
290 cr = GETJSAMPLE(inptr2[col]);
291 /* Range-limiting is essential due to noise introduced by DCT losses. */
292 outptr[0] = range_limit[MAXJSAMPLE - (y + Crrtab[cr])]; /* red */
293 outptr[1] = range_limit[MAXJSAMPLE - (y + /* green */
294 ((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
296 outptr[2] = range_limit[MAXJSAMPLE - (y + Cbbtab[cb])]; /* blue */
297 /* K passes through unchanged */
298 outptr[3] = inptr3[col]; /* don't need GETJSAMPLE here */
306 * Empty method for start_pass.
310 start_pass_dcolor (j_decompress_ptr cinfo)
318 * Module initialization routine for output colorspace conversion.
322 jinit_color_deconverter (j_decompress_ptr cinfo)
324 my_cconvert_ptr cconvert;
327 cconvert = (my_cconvert_ptr)
328 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
329 SIZEOF(my_color_deconverter));
330 cinfo->cconvert = (struct jpeg_color_deconverter *) cconvert;
331 cconvert->pub.start_pass = start_pass_dcolor;
333 /* Make sure num_components agrees with jpeg_color_space */
334 switch (cinfo->jpeg_color_space) {
336 if (cinfo->num_components != 1)
337 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
342 if (cinfo->num_components != 3)
343 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
348 if (cinfo->num_components != 4)
349 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
352 default: /* JCS_UNKNOWN can be anything */
353 if (cinfo->num_components < 1)
354 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
358 /* Set out_color_components and conversion method based on requested space.
359 * Also clear the component_needed flags for any unused components,
360 * so that earlier pipeline stages can avoid useless computation.
363 switch (cinfo->out_color_space) {
365 cinfo->out_color_components = 1;
366 if (cinfo->jpeg_color_space == JCS_GRAYSCALE ||
367 cinfo->jpeg_color_space == JCS_YCbCr) {
368 cconvert->pub.color_convert = grayscale_convert;
369 /* For color->grayscale conversion, only the Y (0) component is needed */
370 for (ci = 1; ci < cinfo->num_components; ci++)
371 cinfo->comp_info[ci].component_needed = FALSE;
373 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
377 cinfo->out_color_components = RGB_PIXELSIZE;
378 if (cinfo->jpeg_color_space == JCS_YCbCr) {
379 cconvert->pub.color_convert = ycc_rgb_convert;
380 build_ycc_rgb_table(cinfo);
381 } else if (cinfo->jpeg_color_space == JCS_GRAYSCALE) {
382 cconvert->pub.color_convert = gray_rgb_convert;
383 } else if (cinfo->jpeg_color_space == JCS_RGB && RGB_PIXELSIZE == 3) {
384 cconvert->pub.color_convert = null_convert;
386 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
390 cinfo->out_color_components = 4;
391 if (cinfo->jpeg_color_space == JCS_YCCK) {
392 cconvert->pub.color_convert = ycck_cmyk_convert;
393 build_ycc_rgb_table(cinfo);
394 } else if (cinfo->jpeg_color_space == JCS_CMYK) {
395 cconvert->pub.color_convert = null_convert;
397 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
401 /* Permit null conversion to same output space */
402 if (cinfo->out_color_space == cinfo->jpeg_color_space) {
403 cinfo->out_color_components = cinfo->num_components;
404 cconvert->pub.color_convert = null_convert;
405 } else /* unsupported non-null conversion */
406 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
410 if (cinfo->quantize_colors)
411 cinfo->output_components = 1; /* single colormapped output component */
413 cinfo->output_components = cinfo->out_color_components;