4 * Copyright (C) 1991-1995, 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
13 #include "radiant_jpeglib.h"
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;
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));
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;
109 * Convert some rows of samples to the output colorspace.
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.
120 ycc_rgb_convert (j_decompress_ptr cinfo,
121 JSAMPIMAGE input_buf, JDIMENSION input_row,
122 JSAMPARRAY output_buf, int num_rows)
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;
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];
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],
153 outptr[RGB_BLUE] = range_limit[y + Cbbtab[cb]];
154 outptr += RGB_PIXELSIZE;
160 /**************** Cases other than YCbCr -> RGB **************/
164 * Color conversion for no colorspace change: just copy the data,
165 * converting from separate-planes to interleaved representation.
169 null_convert (j_decompress_ptr cinfo,
170 JSAMPIMAGE input_buf, JDIMENSION input_row,
171 JSAMPARRAY output_buf, int num_rows)
173 register JSAMPROW inptr, outptr;
174 register JDIMENSION count;
175 register int num_components = cinfo->num_components;
176 JDIMENSION num_cols = cinfo->output_width;
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;
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.
201 grayscale_convert (j_decompress_ptr cinfo,
202 JSAMPIMAGE input_buf, JDIMENSION input_row,
203 JSAMPARRAY output_buf, int num_rows)
205 jcopy_sample_rows(input_buf[0], (int) input_row, output_buf, 0,
206 num_rows, cinfo->output_width);
211 * Adobe-style YCCK->CMYK conversion.
212 * We convert YCbCr to R=1-C, G=1-M, and B=1-Y using the same
213 * conversion as above, while passing K (black) unchanged.
214 * We assume build_ycc_rgb_table has been called.
218 ycck_cmyk_convert (j_decompress_ptr cinfo,
219 JSAMPIMAGE input_buf, JDIMENSION input_row,
220 JSAMPARRAY output_buf, int num_rows)
222 my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
223 register int y, cb, cr;
224 register JSAMPROW outptr;
225 register JSAMPROW inptr0, inptr1, inptr2, inptr3;
226 register JDIMENSION col;
227 JDIMENSION num_cols = cinfo->output_width;
228 /* copy these pointers into registers if possible */
229 register JSAMPLE * range_limit = cinfo->sample_range_limit;
230 register int * Crrtab = cconvert->Cr_r_tab;
231 register int * Cbbtab = cconvert->Cb_b_tab;
232 register INT32 * Crgtab = cconvert->Cr_g_tab;
233 register INT32 * Cbgtab = cconvert->Cb_g_tab;
236 while (--num_rows >= 0) {
237 inptr0 = input_buf[0][input_row];
238 inptr1 = input_buf[1][input_row];
239 inptr2 = input_buf[2][input_row];
240 inptr3 = input_buf[3][input_row];
242 outptr = *output_buf++;
243 for (col = 0; col < num_cols; col++) {
244 y = GETJSAMPLE(inptr0[col]);
245 cb = GETJSAMPLE(inptr1[col]);
246 cr = GETJSAMPLE(inptr2[col]);
247 /* Range-limiting is essential due to noise introduced by DCT losses. */
248 outptr[0] = range_limit[MAXJSAMPLE - (y + Crrtab[cr])]; /* red */
249 outptr[1] = range_limit[MAXJSAMPLE - (y + /* green */
250 ((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
252 outptr[2] = range_limit[MAXJSAMPLE - (y + Cbbtab[cb])]; /* blue */
253 /* K passes through unchanged */
254 outptr[3] = inptr3[col]; /* don't need GETJSAMPLE here */
262 * Empty method for start_pass.
266 start_pass_dcolor (j_decompress_ptr cinfo)
273 * Module initialization routine for output colorspace conversion.
277 jinit_color_deconverter (j_decompress_ptr cinfo)
279 my_cconvert_ptr cconvert;
282 cconvert = (my_cconvert_ptr)
283 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
284 SIZEOF(my_color_deconverter));
285 cinfo->cconvert = (struct jpeg_color_deconverter *) cconvert;
286 cconvert->pub.start_pass = start_pass_dcolor;
288 /* Make sure num_components agrees with jpeg_color_space */
289 switch (cinfo->jpeg_color_space) {
291 if (cinfo->num_components != 1)
292 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
297 if (cinfo->num_components != 3)
298 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
303 if (cinfo->num_components != 4)
304 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
307 default: /* JCS_UNKNOWN can be anything */
308 if (cinfo->num_components < 1)
309 ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
313 /* Set out_color_components and conversion method based on requested space.
314 * Also clear the component_needed flags for any unused components,
315 * so that earlier pipeline stages can avoid useless computation.
318 switch (cinfo->out_color_space) {
320 cinfo->out_color_components = 1;
321 if (cinfo->jpeg_color_space == JCS_GRAYSCALE ||
322 cinfo->jpeg_color_space == JCS_YCbCr) {
323 cconvert->pub.color_convert = grayscale_convert;
324 /* For color->grayscale conversion, only the Y (0) component is needed */
325 for (ci = 1; ci < cinfo->num_components; ci++)
326 cinfo->comp_info[ci].component_needed = FALSE;
328 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
332 cinfo->out_color_components = RGB_PIXELSIZE;
333 if (cinfo->jpeg_color_space == JCS_YCbCr) {
334 cconvert->pub.color_convert = ycc_rgb_convert;
335 build_ycc_rgb_table(cinfo);
336 } else if (cinfo->jpeg_color_space == JCS_RGB && RGB_PIXELSIZE == 3) {
337 cconvert->pub.color_convert = null_convert;
339 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
343 cinfo->out_color_components = 4;
344 if (cinfo->jpeg_color_space == JCS_YCCK) {
345 cconvert->pub.color_convert = ycck_cmyk_convert;
346 build_ycc_rgb_table(cinfo);
347 } else if (cinfo->jpeg_color_space == JCS_CMYK) {
348 cconvert->pub.color_convert = null_convert;
350 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
354 /* Permit null conversion to same output space */
355 if (cinfo->out_color_space == cinfo->jpeg_color_space) {
356 cinfo->out_color_components = cinfo->num_components;
357 cconvert->pub.color_convert = null_convert;
358 } else /* unsupported non-null conversion */
359 ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
363 if (cinfo->quantize_colors)
364 cinfo->output_components = 1; /* single colormapped output component */
366 cinfo->output_components = cinfo->out_color_components;