src/jpeg/jccolor.c

   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 }