dll/3rdparty/libjpeg/jccolor.c

   1 /*
   2  * jccolor.c
   3  *
   4  * Copyright (C) 1991-1996, Thomas G. Lane.
   5  * Modified 2011-2013 by Guido Vollbeding.
   6  * This file is part of the Independent JPEG Group's software.
   7  * For conditions of distribution and use, see the accompanying README file.
   8  *
   9  * This file contains input colorspace conversion routines.
  10  */
  11
  12 #define JPEG_INTERNALS
  13 #include "jinclude.h"
  14 #include "jpeglib.h"
  15
  16
  17 /* Private subobject */
  18
  19 typedef struct {
  20   struct jpeg_color_converter pub; /* public fields */
  21
  22   /* Private state for RGB->YCC conversion */
  23   INT32 * rgb_ycc_tab;          /* => table for RGB to YCbCr conversion */
  24 } my_color_converter;
  25
  26 typedef my_color_converter * my_cconvert_ptr;
  27
  28
  29 /**************** RGB -> YCbCr conversion: most common case **************/
  30
  31 /*
  32  * YCbCr is defined per Recommendation ITU-R BT.601-7 (03/2011),
  33  * previously known as Recommendation CCIR 601-1, except that Cb and Cr
  34  * are normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
  35  * sRGB (standard RGB color space) is defined per IEC 61966-2-1:1999.
  36  * sYCC (standard luma-chroma-chroma color space with extended gamut)
  37  * is defined per IEC 61966-2-1:1999 Amendment A1:2003 Annex F.
  38  * bg-sRGB and bg-sYCC (big gamut standard color spaces)
  39  * are defined per IEC 61966-2-1:1999 Amendment A1:2003 Annex G.
  40  * Note that the derived conversion coefficients given in some of these
  41  * documents are imprecise.  The general conversion equations are
  42  *      Y  = Kr * R + (1 - Kr - Kb) * G + Kb * B
  43  *      Cb = 0.5 * (B - Y) / (1 - Kb)
  44  *      Cr = 0.5 * (R - Y) / (1 - Kr)
  45  * With Kr = 0.299 and Kb = 0.114 (derived according to SMPTE RP 177-1993
  46  * from the 1953 FCC NTSC primaries and CIE Illuminant C),
  47  * the conversion equations to be implemented are therefore
  48  *      Y  =  0.299 * R + 0.587 * G + 0.114 * B
  49  *      Cb = -0.168735892 * R - 0.331264108 * G + 0.5 * B + CENTERJSAMPLE
  50  *      Cr =  0.5 * R - 0.418687589 * G - 0.081312411 * B + CENTERJSAMPLE
  51  * Note: older versions of the IJG code used a zero offset of MAXJSAMPLE/2,
  52  * rather than CENTERJSAMPLE, for Cb and Cr.  This gave equal positive and
  53  * negative swings for Cb/Cr, but meant that grayscale values (Cb=Cr=0)
  54  * were not represented exactly.  Now we sacrifice exact representation of
  55  * maximum red and maximum blue in order to get exact grayscales.
  56  *
  57  * To avoid floating-point arithmetic, we represent the fractional constants
  58  * as integers scaled up by 2^16 (about 4 digits precision); we have to divide
  59  * the products by 2^16, with appropriate rounding, to get the correct answer.
  60  *
  61  * For even more speed, we avoid doing any multiplications in the inner loop
  62  * by precalculating the constants times R,G,B for all possible values.
  63  * For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
  64  * for 9-bit to 12-bit samples it is still acceptable.  It's not very
  65  * reasonable for 16-bit samples, but if you want lossless storage you
  66  * shouldn't be changing colorspace anyway.
  67  * The CENTERJSAMPLE offsets and the rounding fudge-factor of 0.5 are included
  68  * in the tables to save adding them separately in the inner loop.
  69  */
  70
  71 #define SCALEBITS       16      /* speediest right-shift on some machines */
  72 #define CBCR_OFFSET     ((INT32) CENTERJSAMPLE << SCALEBITS)
  73 #define ONE_HALF        ((INT32) 1 << (SCALEBITS-1))
  74 #define FIX(x)          ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
  75
  76 /* We allocate one big table and divide it up into eight parts, instead of
  77  * doing eight alloc_small requests.  This lets us use a single table base
  78  * address, which can be held in a register in the inner loops on many
  79  * machines (more than can hold all eight addresses, anyway).
  80  */
  81
  82 #define R_Y_OFF         0                       /* offset to R => Y section */
  83 #define G_Y_OFF         (1*(MAXJSAMPLE+1))      /* offset to G => Y section */
  84 #define B_Y_OFF         (2*(MAXJSAMPLE+1))      /* etc. */
  85 #define R_CB_OFF        (3*(MAXJSAMPLE+1))
  86 #define G_CB_OFF        (4*(MAXJSAMPLE+1))
  87 #define B_CB_OFF        (5*(MAXJSAMPLE+1))
  88 #define R_CR_OFF        B_CB_OFF                /* B=>Cb, R=>Cr are the same */
  89 #define G_CR_OFF        (6*(MAXJSAMPLE+1))
  90 #define B_CR_OFF        (7*(MAXJSAMPLE+1))
  91 #define TABLE_SIZE      (8*(MAXJSAMPLE+1))
  92
  93
  94 /*
  95  * Initialize for RGB->YCC colorspace conversion.
  96  */
  97
  98 METHODDEF(void)
  99 rgb_ycc_start (j_compress_ptr cinfo)
 100 {
 101   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
 102   INT32 * rgb_ycc_tab;
 103   INT32 i;
 104
 105   /* Allocate and fill in the conversion tables. */
 106   cconvert->rgb_ycc_tab = rgb_ycc_tab = (INT32 *)
 107     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 108                                 (TABLE_SIZE * SIZEOF(INT32)));
 109
 110   for (i = 0; i <= MAXJSAMPLE; i++) {
 111     rgb_ycc_tab[i+R_Y_OFF] = FIX(0.299) * i;
 112     rgb_ycc_tab[i+G_Y_OFF] = FIX(0.587) * i;
 113     rgb_ycc_tab[i+B_Y_OFF] = FIX(0.114) * i   + ONE_HALF;
 114     rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.168735892)) * i;
 115     rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.331264108)) * i;
 116     /* We use a rounding fudge-factor of 0.5-epsilon for Cb and Cr.
 117      * This ensures that the maximum output will round to MAXJSAMPLE
 118      * not MAXJSAMPLE+1, and thus that we don't have to range-limit.
 119      */
 120     rgb_ycc_tab[i+B_CB_OFF] = FIX(0.5) * i    + CBCR_OFFSET + ONE_HALF-1;
 121 /*  B=>Cb and R=>Cr tables are the same
 122     rgb_ycc_tab[i+R_CR_OFF] = FIX(0.5) * i    + CBCR_OFFSET + ONE_HALF-1;
 123 */
 124     rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.418687589)) * i;
 125     rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.081312411)) * i;
 126   }
 127 }
 128
 129
 130 /*
 131  * Convert some rows of samples to the JPEG colorspace.
 132  *
 133  * Note that we change from the application's interleaved-pixel format
 134  * to our internal noninterleaved, one-plane-per-component format.
 135  * The input buffer is therefore three times as wide as the output buffer.
 136  *
 137  * A starting row offset is provided only for the output buffer.  The caller
 138  * can easily adjust the passed input_buf value to accommodate any row
 139  * offset required on that side.
 140  */
 141
 142 METHODDEF(void)
 143 rgb_ycc_convert (j_compress_ptr cinfo,
 144                  JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 145                  JDIMENSION output_row, int num_rows)
 146 {
 147   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
 148   register INT32 * ctab = cconvert->rgb_ycc_tab;
 149   register int r, g, b;
 150   register JSAMPROW inptr;
 151   register JSAMPROW outptr0, outptr1, outptr2;
 152   register JDIMENSION col;
 153   JDIMENSION num_cols = cinfo->image_width;
 154
 155   while (--num_rows >= 0) {
 156     inptr = *input_buf++;
 157     outptr0 = output_buf[0][output_row];
 158     outptr1 = output_buf[1][output_row];
 159     outptr2 = output_buf[2][output_row];
 160     output_row++;
 161     for (col = 0; col < num_cols; col++) {
 162       r = GETJSAMPLE(inptr[RGB_RED]);
 163       g = GETJSAMPLE(inptr[RGB_GREEN]);
 164       b = GETJSAMPLE(inptr[RGB_BLUE]);
 165       /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
 166        * must be too; we do not need an explicit range-limiting operation.
 167        * Hence the value being shifted is never negative, and we don't
 168        * need the general RIGHT_SHIFT macro.
 169        */
 170       /* Y */
 171       outptr0[col] = (JSAMPLE)
 172                 ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
 173                  >> SCALEBITS);
 174       /* Cb */
 175       outptr1[col] = (JSAMPLE)
 176                 ((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
 177                  >> SCALEBITS);
 178       /* Cr */
 179       outptr2[col] = (JSAMPLE)
 180                 ((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
 181                  >> SCALEBITS);
 182       inptr += RGB_PIXELSIZE;
 183     }
 184   }
 185 }
 186
 187
 188 /**************** Cases other than RGB -> YCbCr **************/
 189
 190
 191 /*
 192  * Convert some rows of samples to the JPEG colorspace.
 193  * This version handles RGB->grayscale conversion, which is the same
 194  * as the RGB->Y portion of RGB->YCbCr.
 195  * We assume rgb_ycc_start has been called (we only use the Y tables).
 196  */
 197
 198 METHODDEF(void)
 199 rgb_gray_convert (j_compress_ptr cinfo,
 200                   JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 201                   JDIMENSION output_row, int num_rows)
 202 {
 203   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
 204   register INT32 * ctab = cconvert->rgb_ycc_tab;
 205   register int r, g, b;
 206   register JSAMPROW inptr;
 207   register JSAMPROW outptr;
 208   register JDIMENSION col;
 209   JDIMENSION num_cols = cinfo->image_width;
 210
 211   while (--num_rows >= 0) {
 212     inptr = *input_buf++;
 213     outptr = output_buf[0][output_row++];
 214     for (col = 0; col < num_cols; col++) {
 215       r = GETJSAMPLE(inptr[RGB_RED]);
 216       g = GETJSAMPLE(inptr[RGB_GREEN]);
 217       b = GETJSAMPLE(inptr[RGB_BLUE]);
 218       /* Y */
 219       outptr[col] = (JSAMPLE)
 220                 ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
 221                  >> SCALEBITS);
 222       inptr += RGB_PIXELSIZE;
 223     }
 224   }
 225 }
 226
 227
 228 /*
 229  * Convert some rows of samples to the JPEG colorspace.
 230  * This version handles Adobe-style CMYK->YCCK conversion,
 231  * where we convert R=1-C, G=1-M, and B=1-Y to YCbCr using the same
 232  * conversion as above, while passing K (black) unchanged.
 233  * We assume rgb_ycc_start has been called.
 234  */
 235
 236 METHODDEF(void)
 237 cmyk_ycck_convert (j_compress_ptr cinfo,
 238                    JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 239                    JDIMENSION output_row, int num_rows)
 240 {
 241   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
 242   register INT32 * ctab = cconvert->rgb_ycc_tab;
 243   register int r, g, b;
 244   register JSAMPROW inptr;
 245   register JSAMPROW outptr0, outptr1, outptr2, outptr3;
 246   register JDIMENSION col;
 247   JDIMENSION num_cols = cinfo->image_width;
 248
 249   while (--num_rows >= 0) {
 250     inptr = *input_buf++;
 251     outptr0 = output_buf[0][output_row];
 252     outptr1 = output_buf[1][output_row];
 253     outptr2 = output_buf[2][output_row];
 254     outptr3 = output_buf[3][output_row];
 255     output_row++;
 256     for (col = 0; col < num_cols; col++) {
 257       r = MAXJSAMPLE - GETJSAMPLE(inptr[0]);
 258       g = MAXJSAMPLE - GETJSAMPLE(inptr[1]);
 259       b = MAXJSAMPLE - GETJSAMPLE(inptr[2]);
 260       /* K passes through as-is */
 261       outptr3[col] = inptr[3];  /* don't need GETJSAMPLE here */
 262       /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
 263        * must be too; we do not need an explicit range-limiting operation.
 264        * Hence the value being shifted is never negative, and we don't
 265        * need the general RIGHT_SHIFT macro.
 266        */
 267       /* Y */
 268       outptr0[col] = (JSAMPLE)
 269                 ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
 270                  >> SCALEBITS);
 271       /* Cb */
 272       outptr1[col] = (JSAMPLE)
 273                 ((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
 274                  >> SCALEBITS);
 275       /* Cr */
 276       outptr2[col] = (JSAMPLE)
 277                 ((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
 278                  >> SCALEBITS);
 279       inptr += 4;
 280     }
 281   }
 282 }
 283
 284
 285 /*
 286  * Convert some rows of samples to the JPEG colorspace.
 287  * [R,G,B] to [R-G,G,B-G] conversion with modulo calculation
 288  * (forward reversible color transform).
 289  * This can be seen as an adaption of the general RGB->YCbCr
 290  * conversion equation with Kr = Kb = 0, while replacing the
 291  * normalization by modulo calculation.
 292  */
 293
 294 METHODDEF(void)
 295 rgb_rgb1_convert (j_compress_ptr cinfo,
 296                   JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 297                   JDIMENSION output_row, int num_rows)
 298 {
 299   register int r, g, b;
 300   register JSAMPROW inptr;
 301   register JSAMPROW outptr0, outptr1, outptr2;
 302   register JDIMENSION col;
 303   JDIMENSION num_cols = cinfo->image_width;
 304
 305   while (--num_rows >= 0) {
 306     inptr = *input_buf++;
 307     outptr0 = output_buf[0][output_row];
 308     outptr1 = output_buf[1][output_row];
 309     outptr2 = output_buf[2][output_row];
 310     output_row++;
 311     for (col = 0; col < num_cols; col++) {
 312       r = GETJSAMPLE(inptr[RGB_RED]);
 313       g = GETJSAMPLE(inptr[RGB_GREEN]);
 314       b = GETJSAMPLE(inptr[RGB_BLUE]);
 315       /* Assume that MAXJSAMPLE+1 is a power of 2, so that the MOD
 316        * (modulo) operator is equivalent to the bitmask operator AND.
 317        */
 318       outptr0[col] = (JSAMPLE) ((r - g + CENTERJSAMPLE) & MAXJSAMPLE);
 319       outptr1[col] = (JSAMPLE) g;
 320       outptr2[col] = (JSAMPLE) ((b - g + CENTERJSAMPLE) & MAXJSAMPLE);
 321       inptr += RGB_PIXELSIZE;
 322     }
 323   }
 324 }
 325
 326
 327 /*
 328  * Convert some rows of samples to the JPEG colorspace.
 329  * This version handles grayscale output with no conversion.
 330  * The source can be either plain grayscale or YCC (since Y == gray).
 331  */
 332
 333 METHODDEF(void)
 334 grayscale_convert (j_compress_ptr cinfo,
 335                    JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 336                    JDIMENSION output_row, int num_rows)
 337 {
 338   int instride = cinfo->input_components;
 339   register JSAMPROW inptr;
 340   register JSAMPROW outptr;
 341   register JDIMENSION col;
 342   JDIMENSION num_cols = cinfo->image_width;
 343
 344   while (--num_rows >= 0) {
 345     inptr = *input_buf++;
 346     outptr = output_buf[0][output_row++];
 347     for (col = 0; col < num_cols; col++) {
 348       outptr[col] = inptr[0];   /* don't need GETJSAMPLE() here */
 349       inptr += instride;
 350     }
 351   }
 352 }
 353
 354
 355 /*
 356  * Convert some rows of samples to the JPEG colorspace.
 357  * No colorspace conversion, but change from interleaved
 358  * to separate-planes representation.
 359  */
 360
 361 METHODDEF(void)
 362 rgb_convert (j_compress_ptr cinfo,
 363              JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 364              JDIMENSION output_row, int num_rows)
 365 {
 366   register JSAMPROW inptr;
 367   register JSAMPROW outptr0, outptr1, outptr2;
 368   register JDIMENSION col;
 369   JDIMENSION num_cols = cinfo->image_width;
 370
 371   while (--num_rows >= 0) {
 372     inptr = *input_buf++;
 373     outptr0 = output_buf[0][output_row];
 374     outptr1 = output_buf[1][output_row];
 375     outptr2 = output_buf[2][output_row];
 376     output_row++;
 377     for (col = 0; col < num_cols; col++) {
 378       /* We can dispense with GETJSAMPLE() here */
 379       outptr0[col] = inptr[RGB_RED];
 380       outptr1[col] = inptr[RGB_GREEN];
 381       outptr2[col] = inptr[RGB_BLUE];
 382       inptr += RGB_PIXELSIZE;
 383     }
 384   }
 385 }
 386
 387
 388 /*
 389  * Convert some rows of samples to the JPEG colorspace.
 390  * This version handles multi-component colorspaces without conversion.
 391  * We assume input_components == num_components.
 392  */
 393
 394 METHODDEF(void)
 395 null_convert (j_compress_ptr cinfo,
 396               JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 397               JDIMENSION output_row, int num_rows)
 398 {
 399   int ci;
 400   register int nc = cinfo->num_components;
 401   register JSAMPROW inptr;
 402   register JSAMPROW outptr;
 403   register JDIMENSION col;
 404   JDIMENSION num_cols = cinfo->image_width;
 405
 406   while (--num_rows >= 0) {
 407     /* It seems fastest to make a separate pass for each component. */
 408     for (ci = 0; ci < nc; ci++) {
 409       inptr = input_buf[0] + ci;
 410       outptr = output_buf[ci][output_row];
 411       for (col = 0; col < num_cols; col++) {
 412         *outptr++ = *inptr;     /* don't need GETJSAMPLE() here */
 413         inptr += nc;
 414       }
 415     }
 416     input_buf++;
 417     output_row++;
 418   }
 419 }
 420
 421
 422 /*
 423  * Empty method for start_pass.
 424  */
 425
 426 METHODDEF(void)
 427 null_method (j_compress_ptr cinfo)
 428 {
 429   /* no work needed */
 430 }
 431
 432
 433 /*
 434  * Module initialization routine for input colorspace conversion.
 435  */
 436
 437 GLOBAL(void)
 438 jinit_color_converter (j_compress_ptr cinfo)
 439 {
 440   my_cconvert_ptr cconvert;
 441
 442   cconvert = (my_cconvert_ptr)
 443     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 444                                 SIZEOF(my_color_converter));
 445   cinfo->cconvert = &cconvert->pub;
 446   /* set start_pass to null method until we find out differently */
 447   cconvert->pub.start_pass = null_method;
 448
 449   /* Make sure input_components agrees with in_color_space */
 450   switch (cinfo->in_color_space) {
 451   case JCS_GRAYSCALE:
 452     if (cinfo->input_components != 1)
 453       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
 454     break;
 455
 456   case JCS_RGB:
 457   case JCS_BG_RGB:
 458     if (cinfo->input_components != RGB_PIXELSIZE)
 459       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
 460     break;
 461
 462   case JCS_YCbCr:
 463   case JCS_BG_YCC:
 464     if (cinfo->input_components != 3)
 465       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
 466     break;
 467
 468   case JCS_CMYK:
 469   case JCS_YCCK:
 470     if (cinfo->input_components != 4)
 471       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
 472     break;
 473
 474   default:                      /* JCS_UNKNOWN can be anything */
 475     if (cinfo->input_components < 1)
 476       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
 477     break;
 478   }
 479
 480   /* Support color transform only for RGB colorspaces */
 481   if (cinfo->color_transform &&
 482       cinfo->jpeg_color_space != JCS_RGB &&
 483       cinfo->jpeg_color_space != JCS_BG_RGB)
 484     ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 485
 486   /* Check num_components, set conversion method based on requested space */
 487   switch (cinfo->jpeg_color_space) {
 488   case JCS_GRAYSCALE:
 489     if (cinfo->num_components != 1)
 490       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
 491     switch (cinfo->in_color_space) {
 492     case JCS_GRAYSCALE:
 493     case JCS_YCbCr:
 494     case JCS_BG_YCC:
 495       cconvert->pub.color_convert = grayscale_convert;
 496       break;
 497     case JCS_RGB:
 498       cconvert->pub.start_pass = rgb_ycc_start;
 499       cconvert->pub.color_convert = rgb_gray_convert;
 500       break;
 501     default:
 502       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 503     }
 504     break;
 505
 506   case JCS_RGB:
 507   case JCS_BG_RGB:
 508     if (cinfo->num_components != 3)
 509       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
 510     if (cinfo->in_color_space == cinfo->jpeg_color_space) {
 511       switch (cinfo->color_transform) {
 512       case JCT_NONE:
 513         cconvert->pub.color_convert = rgb_convert;
 514         break;
 515       case JCT_SUBTRACT_GREEN:
 516         cconvert->pub.color_convert = rgb_rgb1_convert;
 517         break;
 518       default:
 519         ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 520       }
 521     } else
 522       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 523     break;
 524
 525   case JCS_YCbCr:
 526     if (cinfo->num_components != 3)
 527       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
 528     switch (cinfo->in_color_space) {
 529     case JCS_RGB:
 530       cconvert->pub.start_pass = rgb_ycc_start;
 531       cconvert->pub.color_convert = rgb_ycc_convert;
 532       break;
 533     case JCS_YCbCr:
 534       cconvert->pub.color_convert = null_convert;
 535       break;
 536     default:
 537       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 538     }
 539     break;
 540
 541   case JCS_BG_YCC:
 542     if (cinfo->num_components != 3)
 543       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
 544     switch (cinfo->in_color_space) {
 545     case JCS_RGB:
 546       /* For conversion from normal RGB input to BG_YCC representation,
 547        * the Cb/Cr values are first computed as usual, and then
 548        * quantized further after DCT processing by a factor of
 549        * 2 in reference to the nominal quantization factor.
 550        */
 551       /* need quantization scale by factor of 2 after DCT */
 552       cinfo->comp_info[1].component_needed = TRUE;
 553       cinfo->comp_info[2].component_needed = TRUE;
 554       /* compute normal YCC first */
 555       cconvert->pub.start_pass = rgb_ycc_start;
 556       cconvert->pub.color_convert = rgb_ycc_convert;
 557       break;
 558     case JCS_YCbCr:
 559       /* need quantization scale by factor of 2 after DCT */
 560       cinfo->comp_info[1].component_needed = TRUE;
 561       cinfo->comp_info[2].component_needed = TRUE;
 562       /*FALLTHROUGH*/
 563     case JCS_BG_YCC:
 564       /* Pass through for BG_YCC input */
 565       cconvert->pub.color_convert = null_convert;
 566       break;
 567     default:
 568       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 569     }
 570     break;
 571
 572   case JCS_CMYK:
 573     if (cinfo->num_components != 4)
 574       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
 575     if (cinfo->in_color_space == JCS_CMYK)
 576       cconvert->pub.color_convert = null_convert;
 577     else
 578       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 579     break;
 580
 581   case JCS_YCCK:
 582     if (cinfo->num_components != 4)
 583       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
 584     switch (cinfo->in_color_space) {
 585     case JCS_CMYK:
 586       cconvert->pub.start_pass = rgb_ycc_start;
 587       cconvert->pub.color_convert = cmyk_ycck_convert;
 588       break;
 589     case JCS_YCCK:
 590       cconvert->pub.color_convert = null_convert;
 591       break;
 592     default:
 593       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 594     }
 595     break;
 596
 597   default:                      /* allow null conversion of JCS_UNKNOWN */
 598     if (cinfo->jpeg_color_space != cinfo->in_color_space ||
 599         cinfo->num_components != cinfo->input_components)
 600       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
 601     cconvert->pub.color_convert = null_convert;
 602     break;
 603   }
 604 }