src/jpeg/jdcolor.c

   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 }