jpeg/jquant1.c

   1 /*
   2  * jquant1.c
   3  *
   4  * Copyright (C) 1991-1996, Thomas G. Lane.
   5  * Copyright (C) 2009, D. R. Commander
   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 1-pass color quantization (color mapping) routines.
  10  * These routines provide mapping to a fixed color map using equally spaced
  11  * color values.  Optional Floyd-Steinberg or ordered dithering is available.
  12  */
  13
  14 #define JPEG_INTERNALS
  15 #include "jinclude.h"
  16 #include "jpeglib.h"
  17
  18 #ifdef QUANT_1PASS_SUPPORTED
  19
  20
  21 /*
  22  * The main purpose of 1-pass quantization is to provide a fast, if not very
  23  * high quality, colormapped output capability.  A 2-pass quantizer usually
  24  * gives better visual quality; however, for quantized grayscale output this
  25  * quantizer is perfectly adequate.  Dithering is highly recommended with this
  26  * quantizer, though you can turn it off if you really want to.
  27  *
  28  * In 1-pass quantization the colormap must be chosen in advance of seeing the
  29  * image.  We use a map consisting of all combinations of Ncolors[i] color
  30  * values for the i'th component.  The Ncolors[] values are chosen so that
  31  * their product, the total number of colors, is no more than that requested.
  32  * (In most cases, the product will be somewhat less.)
  33  *
  34  * Since the colormap is orthogonal, the representative value for each color
  35  * component can be determined without considering the other components;
  36  * then these indexes can be combined into a colormap index by a standard
  37  * N-dimensional-array-subscript calculation.  Most of the arithmetic involved
  38  * can be precalculated and stored in the lookup table colorindex[].
  39  * colorindex[i][j] maps pixel value j in component i to the nearest
  40  * representative value (grid plane) for that component; this index is
  41  * multiplied by the array stride for component i, so that the
  42  * index of the colormap entry closest to a given pixel value is just
  43  *    sum( colorindex[component-number][pixel-component-value] )
  44  * Aside from being fast, this scheme allows for variable spacing between
  45  * representative values with no additional lookup cost.
  46  *
  47  * If gamma correction has been applied in color conversion, it might be wise
  48  * to adjust the color grid spacing so that the representative colors are
  49  * equidistant in linear space.  At this writing, gamma correction is not
  50  * implemented by jdcolor, so nothing is done here.
  51  */
  52
  53
  54 /* Declarations for ordered dithering.
  55  *
  56  * We use a standard 16x16 ordered dither array.  The basic concept of ordered
  57  * dithering is described in many references, for instance Dale Schumacher's
  58  * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
  59  * In place of Schumacher's comparisons against a "threshold" value, we add a
  60  * "dither" value to the input pixel and then round the result to the nearest
  61  * output value.  The dither value is equivalent to (0.5 - threshold) times
  62  * the distance between output values.  For ordered dithering, we assume that
  63  * the output colors are equally spaced; if not, results will probably be
  64  * worse, since the dither may be too much or too little at a given point.
  65  *
  66  * The normal calculation would be to form pixel value + dither, range-limit
  67  * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.
  68  * We can skip the separate range-limiting step by extending the colorindex
  69  * table in both directions.
  70  */
  71
  72 #define ODITHER_SIZE  16        /* dimension of dither matrix */
  73 /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
  74 #define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE)       /* # cells in matrix */
  75 #define ODITHER_MASK  (ODITHER_SIZE-1) /* mask for wrapping around counters */
  76
  77 typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
  78 typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];
  79
  80 static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {
  81   /* Bayer's order-4 dither array.  Generated by the code given in
  82    * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
  83    * The values in this array must range from 0 to ODITHER_CELLS-1.
  84    */
  85   {   0,192, 48,240, 12,204, 60,252,  3,195, 51,243, 15,207, 63,255 },
  86   { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },
  87   {  32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },
  88   { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },
  89   {   8,200, 56,248,  4,196, 52,244, 11,203, 59,251,  7,199, 55,247 },
  90   { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },
  91   {  40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },
  92   { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },
  93   {   2,194, 50,242, 14,206, 62,254,  1,193, 49,241, 13,205, 61,253 },
  94   { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },
  95   {  34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },
  96   { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },
  97   {  10,202, 58,250,  6,198, 54,246,  9,201, 57,249,  5,197, 53,245 },
  98   { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },
  99   {  42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },
 100   { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }
 101 };
 102
 103
 104 /* Declarations for Floyd-Steinberg dithering.
 105  *
 106  * Errors are accumulated into the array fserrors[], at a resolution of
 107  * 1/16th of a pixel count.  The error at a given pixel is propagated
 108  * to its not-yet-processed neighbors using the standard F-S fractions,
 109  *              ...     (here)  7/16
 110  *              3/16    5/16    1/16
 111  * We work left-to-right on even rows, right-to-left on odd rows.
 112  *
 113  * We can get away with a single array (holding one row's worth of errors)
 114  * by using it to store the current row's errors at pixel columns not yet
 115  * processed, but the next row's errors at columns already processed.  We
 116  * need only a few extra variables to hold the errors immediately around the
 117  * current column.  (If we are lucky, those variables are in registers, but
 118  * even if not, they're probably cheaper to access than array elements are.)
 119  *
 120  * The fserrors[] array is indexed [component#][position].
 121  * We provide (#columns + 2) entries per component; the extra entry at each
 122  * end saves us from special-casing the first and last pixels.
 123  *
 124  * Note: on a wide image, we might not have enough room in a PC's near data
 125  * segment to hold the error array; so it is allocated with alloc_large.
 126  */
 127
 128 #if BITS_IN_JSAMPLE == 8
 129 typedef INT16 FSERROR;          /* 16 bits should be enough */
 130 typedef int LOCFSERROR;         /* use 'int' for calculation temps */
 131 #else
 132 typedef INT32 FSERROR;          /* may need more than 16 bits */
 133 typedef INT32 LOCFSERROR;       /* be sure calculation temps are big enough */
 134 #endif
 135
 136 typedef FSERROR FAR *FSERRPTR;  /* pointer to error array (in FAR storage!) */
 137
 138
 139 /* Private subobject */
 140
 141 #define MAX_Q_COMPS 4           /* max components I can handle */
 142
 143 typedef struct {
 144   struct jpeg_color_quantizer pub; /* public fields */
 145
 146   /* Initially allocated colormap is saved here */
 147   JSAMPARRAY sv_colormap;       /* The color map as a 2-D pixel array */
 148   int sv_actual;                /* number of entries in use */
 149
 150   JSAMPARRAY colorindex;        /* Precomputed mapping for speed */
 151   /* colorindex[i][j] = index of color closest to pixel value j in component i,
 152    * premultiplied as described above.  Since colormap indexes must fit into
 153    * JSAMPLEs, the entries of this array will too.
 154    */
 155   boolean is_padded;            /* is the colorindex padded for odither? */
 156
 157   int Ncolors[MAX_Q_COMPS];     /* # of values alloced to each component */
 158
 159   /* Variables for ordered dithering */
 160   int row_index;                /* cur row's vertical index in dither matrix */
 161   ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */
 162
 163   /* Variables for Floyd-Steinberg dithering */
 164   FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */
 165   boolean on_odd_row;           /* flag to remember which row we are on */
 166 } my_cquantizer;
 167
 168 typedef my_cquantizer * my_cquantize_ptr;
 169
 170
 171 /*
 172  * Policy-making subroutines for create_colormap and create_colorindex.
 173  * These routines determine the colormap to be used.  The rest of the module
 174  * only assumes that the colormap is orthogonal.
 175  *
 176  *  * select_ncolors decides how to divvy up the available colors
 177  *    among the components.
 178  *  * output_value defines the set of representative values for a component.
 179  *  * largest_input_value defines the mapping from input values to
 180  *    representative values for a component.
 181  * Note that the latter two routines may impose different policies for
 182  * different components, though this is not currently done.
 183  */
 184
 185
 186 LOCAL(int)
 187 select_ncolors (j_decompress_ptr cinfo, int Ncolors[])
 188 /* Determine allocation of desired colors to components, */
 189 /* and fill in Ncolors[] array to indicate choice. */
 190 /* Return value is total number of colors (product of Ncolors[] values). */
 191 {
 192   int nc = cinfo->out_color_components; /* number of color components */
 193   int max_colors = cinfo->desired_number_of_colors;
 194   int total_colors, iroot, i, j;
 195   boolean changed;
 196   long temp;
 197   int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE };
 198   RGB_order[0] = rgb_green[cinfo->out_color_space];
 199   RGB_order[1] = rgb_red[cinfo->out_color_space];
 200   RGB_order[2] = rgb_blue[cinfo->out_color_space];
 201
 202   /* We can allocate at least the nc'th root of max_colors per component. */
 203   /* Compute floor(nc'th root of max_colors). */
 204   iroot = 1;
 205   do {
 206     iroot++;
 207     temp = iroot;               /* set temp = iroot ** nc */
 208     for (i = 1; i < nc; i++)
 209       temp *= iroot;
 210   } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */
 211   iroot--;                      /* now iroot = floor(root) */
 212
 213   /* Must have at least 2 color values per component */
 214   if (iroot < 2)
 215     ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp);
 216
 217   /* Initialize to iroot color values for each component */
 218   total_colors = 1;
 219   for (i = 0; i < nc; i++) {
 220     Ncolors[i] = iroot;
 221     total_colors *= iroot;
 222   }
 223   /* We may be able to increment the count for one or more components without
 224    * exceeding max_colors, though we know not all can be incremented.
 225    * Sometimes, the first component can be incremented more than once!
 226    * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)
 227    * In RGB colorspace, try to increment G first, then R, then B.
 228    */
 229   do {
 230     changed = FALSE;
 231     for (i = 0; i < nc; i++) {
 232       j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i);
 233       /* calculate new total_colors if Ncolors[j] is incremented */
 234       temp = total_colors / Ncolors[j];
 235       temp *= Ncolors[j]+1;     /* done in long arith to avoid oflo */
 236       if (temp > (long) max_colors)
 237         break;                  /* won't fit, done with this pass */
 238       Ncolors[j]++;             /* OK, apply the increment */
 239       total_colors = (int) temp;
 240       changed = TRUE;
 241     }
 242   } while (changed);
 243
 244   return total_colors;
 245 }
 246
 247
 248 LOCAL(int)
 249 output_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
 250 /* Return j'th output value, where j will range from 0 to maxj */
 251 /* The output values must fall in 0..MAXJSAMPLE in increasing order */
 252 {
 253   /* We always provide values 0 and MAXJSAMPLE for each component;
 254    * any additional values are equally spaced between these limits.
 255    * (Forcing the upper and lower values to the limits ensures that
 256    * dithering can't produce a color outside the selected gamut.)
 257    */
 258   return (int) (((INT32) j * MAXJSAMPLE + maxj/2) / maxj);
 259 }
 260
 261
 262 LOCAL(int)
 263 largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
 264 /* Return largest input value that should map to j'th output value */
 265 /* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */
 266 {
 267   /* Breakpoints are halfway between values returned by output_value */
 268   return (int) (((INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj));
 269 }
 270
 271
 272 /*
 273  * Create the colormap.
 274  */
 275
 276 LOCAL(void)
 277 create_colormap (j_decompress_ptr cinfo)
 278 {
 279   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 280   JSAMPARRAY colormap;          /* Created colormap */
 281   int total_colors;             /* Number of distinct output colors */
 282   int i,j,k, nci, blksize, blkdist, ptr, val;
 283
 284   /* Select number of colors for each component */
 285   total_colors = select_ncolors(cinfo, cquantize->Ncolors);
 286
 287   /* Report selected color counts */
 288   if (cinfo->out_color_components == 3)
 289     TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS,
 290              total_colors, cquantize->Ncolors[0],
 291              cquantize->Ncolors[1], cquantize->Ncolors[2]);
 292   else
 293     TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors);
 294
 295   /* Allocate and fill in the colormap. */
 296   /* The colors are ordered in the map in standard row-major order, */
 297   /* i.e. rightmost (highest-indexed) color changes most rapidly. */
 298
 299   colormap = (*cinfo->mem->alloc_sarray)
 300     ((j_common_ptr) cinfo, JPOOL_IMAGE,
 301      (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components);
 302
 303   /* blksize is number of adjacent repeated entries for a component */
 304   /* blkdist is distance between groups of identical entries for a component */
 305   blkdist = total_colors;
 306
 307   for (i = 0; i < cinfo->out_color_components; i++) {
 308     /* fill in colormap entries for i'th color component */
 309     nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
 310     blksize = blkdist / nci;
 311     for (j = 0; j < nci; j++) {
 312       /* Compute j'th output value (out of nci) for component */
 313       val = output_value(cinfo, i, j, nci-1);
 314       /* Fill in all colormap entries that have this value of this component */
 315       for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) {
 316         /* fill in blksize entries beginning at ptr */
 317         for (k = 0; k < blksize; k++)
 318           colormap[i][ptr+k] = (JSAMPLE) val;
 319       }
 320     }
 321     blkdist = blksize;          /* blksize of this color is blkdist of next */
 322   }
 323
 324   /* Save the colormap in private storage,
 325    * where it will survive color quantization mode changes.
 326    */
 327   cquantize->sv_colormap = colormap;
 328   cquantize->sv_actual = total_colors;
 329 }
 330
 331
 332 /*
 333  * Create the color index table.
 334  */
 335
 336 LOCAL(void)
 337 create_colorindex (j_decompress_ptr cinfo)
 338 {
 339   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 340   JSAMPROW indexptr;
 341   int i,j,k, nci, blksize, val, pad;
 342
 343   /* For ordered dither, we pad the color index tables by MAXJSAMPLE in
 344    * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE).
 345    * This is not necessary in the other dithering modes.  However, we
 346    * flag whether it was done in case user changes dithering mode.
 347    */
 348   if (cinfo->dither_mode == JDITHER_ORDERED) {
 349     pad = MAXJSAMPLE*2;
 350     cquantize->is_padded = TRUE;
 351   } else {
 352     pad = 0;
 353     cquantize->is_padded = FALSE;
 354   }
 355
 356   cquantize->colorindex = (*cinfo->mem->alloc_sarray)
 357     ((j_common_ptr) cinfo, JPOOL_IMAGE,
 358      (JDIMENSION) (MAXJSAMPLE+1 + pad),
 359      (JDIMENSION) cinfo->out_color_components);
 360
 361   /* blksize is number of adjacent repeated entries for a component */
 362   blksize = cquantize->sv_actual;
 363
 364   for (i = 0; i < cinfo->out_color_components; i++) {
 365     /* fill in colorindex entries for i'th color component */
 366     nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
 367     blksize = blksize / nci;
 368
 369     /* adjust colorindex pointers to provide padding at negative indexes. */
 370     if (pad)
 371       cquantize->colorindex[i] += MAXJSAMPLE;
 372
 373     /* in loop, val = index of current output value, */
 374     /* and k = largest j that maps to current val */
 375     indexptr = cquantize->colorindex[i];
 376     val = 0;
 377     k = largest_input_value(cinfo, i, 0, nci-1);
 378     for (j = 0; j <= MAXJSAMPLE; j++) {
 379       while (j > k)             /* advance val if past boundary */
 380         k = largest_input_value(cinfo, i, ++val, nci-1);
 381       /* premultiply so that no multiplication needed in main processing */
 382       indexptr[j] = (JSAMPLE) (val * blksize);
 383     }
 384     /* Pad at both ends if necessary */
 385     if (pad)
 386       for (j = 1; j <= MAXJSAMPLE; j++) {
 387         indexptr[-j] = indexptr[0];
 388         indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE];
 389       }
 390   }
 391 }
 392
 393
 394 /*
 395  * Create an ordered-dither array for a component having ncolors
 396  * distinct output values.
 397  */
 398
 399 LOCAL(ODITHER_MATRIX_PTR)
 400 make_odither_array (j_decompress_ptr cinfo, int ncolors)
 401 {
 402   ODITHER_MATRIX_PTR odither;
 403   int j,k;
 404   INT32 num,den;
 405
 406   odither = (ODITHER_MATRIX_PTR)
 407     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 408                                 SIZEOF(ODITHER_MATRIX));
 409   /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1).
 410    * Hence the dither value for the matrix cell with fill order f
 411    * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1).
 412    * On 16-bit-int machine, be careful to avoid overflow.
 413    */
 414   den = 2 * ODITHER_CELLS * ((INT32) (ncolors - 1));
 415   for (j = 0; j < ODITHER_SIZE; j++) {
 416     for (k = 0; k < ODITHER_SIZE; k++) {
 417       num = ((INT32) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k])))
 418             * MAXJSAMPLE;
 419       /* Ensure round towards zero despite C's lack of consistency
 420        * about rounding negative values in integer division...
 421        */
 422       odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den);
 423     }
 424   }
 425   return odither;
 426 }
 427
 428
 429 /*
 430  * Create the ordered-dither tables.
 431  * Components having the same number of representative colors may
 432  * share a dither table.
 433  */
 434
 435 LOCAL(void)
 436 create_odither_tables (j_decompress_ptr cinfo)
 437 {
 438   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 439   ODITHER_MATRIX_PTR odither;
 440   int i, j, nci;
 441
 442   for (i = 0; i < cinfo->out_color_components; i++) {
 443     nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
 444     odither = NULL;             /* search for matching prior component */
 445     for (j = 0; j < i; j++) {
 446       if (nci == cquantize->Ncolors[j]) {
 447         odither = cquantize->odither[j];
 448         break;
 449       }
 450     }
 451     if (odither == NULL)        /* need a new table? */
 452       odither = make_odither_array(cinfo, nci);
 453     cquantize->odither[i] = odither;
 454   }
 455 }
 456
 457
 458 /*
 459  * Map some rows of pixels to the output colormapped representation.
 460  */
 461
 462 METHODDEF(void)
 463 color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
 464                 JSAMPARRAY output_buf, int num_rows)
 465 /* General case, no dithering */
 466 {
 467   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 468   JSAMPARRAY colorindex = cquantize->colorindex;
 469   register int pixcode, ci;
 470   register JSAMPROW ptrin, ptrout;
 471   int row;
 472   JDIMENSION col;
 473   JDIMENSION width = cinfo->output_width;
 474   register int nc = cinfo->out_color_components;
 475
 476   for (row = 0; row < num_rows; row++) {
 477     ptrin = input_buf[row];
 478     ptrout = output_buf[row];
 479     for (col = width; col > 0; col--) {
 480       pixcode = 0;
 481       for (ci = 0; ci < nc; ci++) {
 482         pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]);
 483       }
 484       *ptrout++ = (JSAMPLE) pixcode;
 485     }
 486   }
 487 }
 488
 489
 490 METHODDEF(void)
 491 color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
 492                  JSAMPARRAY output_buf, int num_rows)
 493 /* Fast path for out_color_components==3, no dithering */
 494 {
 495   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 496   register int pixcode;
 497   register JSAMPROW ptrin, ptrout;
 498   JSAMPROW colorindex0 = cquantize->colorindex[0];
 499   JSAMPROW colorindex1 = cquantize->colorindex[1];
 500   JSAMPROW colorindex2 = cquantize->colorindex[2];
 501   int row;
 502   JDIMENSION col;
 503   JDIMENSION width = cinfo->output_width;
 504
 505   for (row = 0; row < num_rows; row++) {
 506     ptrin = input_buf[row];
 507     ptrout = output_buf[row];
 508     for (col = width; col > 0; col--) {
 509       pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]);
 510       pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]);
 511       pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]);
 512       *ptrout++ = (JSAMPLE) pixcode;
 513     }
 514   }
 515 }
 516
 517
 518 METHODDEF(void)
 519 quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
 520                      JSAMPARRAY output_buf, int num_rows)
 521 /* General case, with ordered dithering */
 522 {
 523   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 524   register JSAMPROW input_ptr;
 525   register JSAMPROW output_ptr;
 526   JSAMPROW colorindex_ci;
 527   int * dither;                 /* points to active row of dither matrix */
 528   int row_index, col_index;     /* current indexes into dither matrix */
 529   int nc = cinfo->out_color_components;
 530   int ci;
 531   int row;
 532   JDIMENSION col;
 533   JDIMENSION width = cinfo->output_width;
 534
 535   for (row = 0; row < num_rows; row++) {
 536     /* Initialize output values to 0 so can process components separately */
 537     jzero_far((void FAR *) output_buf[row],
 538               (size_t) (width * SIZEOF(JSAMPLE)));
 539     row_index = cquantize->row_index;
 540     for (ci = 0; ci < nc; ci++) {
 541       input_ptr = input_buf[row] + ci;
 542       output_ptr = output_buf[row];
 543       colorindex_ci = cquantize->colorindex[ci];
 544       dither = cquantize->odither[ci][row_index];
 545       col_index = 0;
 546
 547       for (col = width; col > 0; col--) {
 548         /* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,
 549          * select output value, accumulate into output code for this pixel.
 550          * Range-limiting need not be done explicitly, as we have extended
 551          * the colorindex table to produce the right answers for out-of-range
 552          * inputs.  The maximum dither is +- MAXJSAMPLE; this sets the
 553          * required amount of padding.
 554          */
 555         *output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]];
 556         input_ptr += nc;
 557         output_ptr++;
 558         col_index = (col_index + 1) & ODITHER_MASK;
 559       }
 560     }
 561     /* Advance row index for next row */
 562     row_index = (row_index + 1) & ODITHER_MASK;
 563     cquantize->row_index = row_index;
 564   }
 565 }
 566
 567
 568 METHODDEF(void)
 569 quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
 570                       JSAMPARRAY output_buf, int num_rows)
 571 /* Fast path for out_color_components==3, with ordered dithering */
 572 {
 573   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 574   register int pixcode;
 575   register JSAMPROW input_ptr;
 576   register JSAMPROW output_ptr;
 577   JSAMPROW colorindex0 = cquantize->colorindex[0];
 578   JSAMPROW colorindex1 = cquantize->colorindex[1];
 579   JSAMPROW colorindex2 = cquantize->colorindex[2];
 580   int * dither0;                /* points to active row of dither matrix */
 581   int * dither1;
 582   int * dither2;
 583   int row_index, col_index;     /* current indexes into dither matrix */
 584   int row;
 585   JDIMENSION col;
 586   JDIMENSION width = cinfo->output_width;
 587
 588   for (row = 0; row < num_rows; row++) {
 589     row_index = cquantize->row_index;
 590     input_ptr = input_buf[row];
 591     output_ptr = output_buf[row];
 592     dither0 = cquantize->odither[0][row_index];
 593     dither1 = cquantize->odither[1][row_index];
 594     dither2 = cquantize->odither[2][row_index];
 595     col_index = 0;
 596
 597     for (col = width; col > 0; col--) {
 598       pixcode  = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) +
 599                                         dither0[col_index]]);
 600       pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) +
 601                                         dither1[col_index]]);
 602       pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) +
 603                                         dither2[col_index]]);
 604       *output_ptr++ = (JSAMPLE) pixcode;
 605       col_index = (col_index + 1) & ODITHER_MASK;
 606     }
 607     row_index = (row_index + 1) & ODITHER_MASK;
 608     cquantize->row_index = row_index;
 609   }
 610 }
 611
 612
 613 METHODDEF(void)
 614 quantize_fs_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
 615                     JSAMPARRAY output_buf, int num_rows)
 616 /* General case, with Floyd-Steinberg dithering */
 617 {
 618   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 619   register LOCFSERROR cur;      /* current error or pixel value */
 620   LOCFSERROR belowerr;          /* error for pixel below cur */
 621   LOCFSERROR bpreverr;          /* error for below/prev col */
 622   LOCFSERROR bnexterr;          /* error for below/next col */
 623   LOCFSERROR delta;
 624   register FSERRPTR errorptr;   /* => fserrors[] at column before current */
 625   register JSAMPROW input_ptr;
 626   register JSAMPROW output_ptr;
 627   JSAMPROW colorindex_ci;
 628   JSAMPROW colormap_ci;
 629   int pixcode;
 630   int nc = cinfo->out_color_components;
 631   int dir;                      /* 1 for left-to-right, -1 for right-to-left */
 632   int dirnc;                    /* dir * nc */
 633   int ci;
 634   int row;
 635   JDIMENSION col;
 636   JDIMENSION width = cinfo->output_width;
 637   JSAMPLE *range_limit = cinfo->sample_range_limit;
 638   SHIFT_TEMPS
 639
 640   for (row = 0; row < num_rows; row++) {
 641     /* Initialize output values to 0 so can process components separately */
 642     jzero_far((void FAR *) output_buf[row],
 643               (size_t) (width * SIZEOF(JSAMPLE)));
 644     for (ci = 0; ci < nc; ci++) {
 645       input_ptr = input_buf[row] + ci;
 646       output_ptr = output_buf[row];
 647       if (cquantize->on_odd_row) {
 648         /* work right to left in this row */
 649         input_ptr += (width-1) * nc; /* so point to rightmost pixel */
 650         output_ptr += width-1;
 651         dir = -1;
 652         dirnc = -nc;
 653         errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */
 654       } else {
 655         /* work left to right in this row */
 656         dir = 1;
 657         dirnc = nc;
 658         errorptr = cquantize->fserrors[ci]; /* => entry before first column */
 659       }
 660       colorindex_ci = cquantize->colorindex[ci];
 661       colormap_ci = cquantize->sv_colormap[ci];
 662       /* Preset error values: no error propagated to first pixel from left */
 663       cur = 0;
 664       /* and no error propagated to row below yet */
 665       belowerr = bpreverr = 0;
 666
 667       for (col = width; col > 0; col--) {
 668         /* cur holds the error propagated from the previous pixel on the
 669          * current line.  Add the error propagated from the previous line
 670          * to form the complete error correction term for this pixel, and
 671          * round the error term (which is expressed * 16) to an integer.
 672          * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
 673          * for either sign of the error value.
 674          * Note: errorptr points to *previous* column's array entry.
 675          */
 676         cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4);
 677         /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
 678          * The maximum error is +- MAXJSAMPLE; this sets the required size
 679          * of the range_limit array.
 680          */
 681         cur += GETJSAMPLE(*input_ptr);
 682         cur = GETJSAMPLE(range_limit[cur]);
 683         /* Select output value, accumulate into output code for this pixel */
 684         pixcode = GETJSAMPLE(colorindex_ci[cur]);
 685         *output_ptr += (JSAMPLE) pixcode;
 686         /* Compute actual representation error at this pixel */
 687         /* Note: we can do this even though we don't have the final */
 688         /* pixel code, because the colormap is orthogonal. */
 689         cur -= GETJSAMPLE(colormap_ci[pixcode]);
 690         /* Compute error fractions to be propagated to adjacent pixels.
 691          * Add these into the running sums, and simultaneously shift the
 692          * next-line error sums left by 1 column.
 693          */
 694         bnexterr = cur;
 695         delta = cur * 2;
 696         cur += delta;           /* form error * 3 */
 697         errorptr[0] = (FSERROR) (bpreverr + cur);
 698         cur += delta;           /* form error * 5 */
 699         bpreverr = belowerr + cur;
 700         belowerr = bnexterr;
 701         cur += delta;           /* form error * 7 */
 702         /* At this point cur contains the 7/16 error value to be propagated
 703          * to the next pixel on the current line, and all the errors for the
 704          * next line have been shifted over. We are therefore ready to move on.
 705          */
 706         input_ptr += dirnc;     /* advance input ptr to next column */
 707         output_ptr += dir;      /* advance output ptr to next column */
 708         errorptr += dir;        /* advance errorptr to current column */
 709       }
 710       /* Post-loop cleanup: we must unload the final error value into the
 711        * final fserrors[] entry.  Note we need not unload belowerr because
 712        * it is for the dummy column before or after the actual array.
 713        */
 714       errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */
 715     }
 716     cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);
 717   }
 718 }
 719
 720
 721 /*
 722  * Allocate workspace for Floyd-Steinberg errors.
 723  */
 724
 725 LOCAL(void)
 726 alloc_fs_workspace (j_decompress_ptr cinfo)
 727 {
 728   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 729   size_t arraysize;
 730   int i;
 731
 732   arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
 733   for (i = 0; i < cinfo->out_color_components; i++) {
 734     cquantize->fserrors[i] = (FSERRPTR)
 735       (*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize);
 736   }
 737 }
 738
 739
 740 /*
 741  * Initialize for one-pass color quantization.
 742  */
 743
 744 METHODDEF(void)
 745 start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan)
 746 {
 747   my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
 748   size_t arraysize;
 749   int i;
 750
 751   /* Install my colormap. */
 752   cinfo->colormap = cquantize->sv_colormap;
 753   cinfo->actual_number_of_colors = cquantize->sv_actual;
 754
 755   /* Initialize for desired dithering mode. */
 756   switch (cinfo->dither_mode) {
 757   case JDITHER_NONE:
 758     if (cinfo->out_color_components == 3)
 759       cquantize->pub.color_quantize = color_quantize3;
 760     else
 761       cquantize->pub.color_quantize = color_quantize;
 762     break;
 763   case JDITHER_ORDERED:
 764     if (cinfo->out_color_components == 3)
 765       cquantize->pub.color_quantize = quantize3_ord_dither;
 766     else
 767       cquantize->pub.color_quantize = quantize_ord_dither;
 768     cquantize->row_index = 0;   /* initialize state for ordered dither */
 769     /* If user changed to ordered dither from another mode,
 770      * we must recreate the color index table with padding.
 771      * This will cost extra space, but probably isn't very likely.
 772      */
 773     if (! cquantize->is_padded)
 774       create_colorindex(cinfo);
 775     /* Create ordered-dither tables if we didn't already. */
 776     if (cquantize->odither[0] == NULL)
 777       create_odither_tables(cinfo);
 778     break;
 779   case JDITHER_FS:
 780     cquantize->pub.color_quantize = quantize_fs_dither;
 781     cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */
 782     /* Allocate Floyd-Steinberg workspace if didn't already. */
 783     if (cquantize->fserrors[0] == NULL)
 784       alloc_fs_workspace(cinfo);
 785     /* Initialize the propagated errors to zero. */
 786     arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
 787     for (i = 0; i < cinfo->out_color_components; i++)
 788       jzero_far((void FAR *) cquantize->fserrors[i], arraysize);
 789     break;
 790   default:
 791     ERREXIT(cinfo, JERR_NOT_COMPILED);
 792     break;
 793   }
 794 }
 795
 796
 797 /*
 798  * Finish up at the end of the pass.
 799  */
 800
 801 METHODDEF(void)
 802 finish_pass_1_quant (j_decompress_ptr cinfo)
 803 {
 804   /* no work in 1-pass case */
 805 }
 806
 807
 808 /*
 809  * Switch to a new external colormap between output passes.
 810  * Shouldn't get to this module!
 811  */
 812
 813 METHODDEF(void)
 814 new_color_map_1_quant (j_decompress_ptr cinfo)
 815 {
 816   ERREXIT(cinfo, JERR_MODE_CHANGE);
 817 }
 818
 819
 820 /*
 821  * Module initialization routine for 1-pass color quantization.
 822  */
 823
 824 GLOBAL(void)
 825 jinit_1pass_quantizer (j_decompress_ptr cinfo)
 826 {
 827   my_cquantize_ptr cquantize;
 828
 829   cquantize = (my_cquantize_ptr)
 830     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 831                                 SIZEOF(my_cquantizer));
 832   cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;
 833   cquantize->pub.start_pass = start_pass_1_quant;
 834   cquantize->pub.finish_pass = finish_pass_1_quant;
 835   cquantize->pub.new_color_map = new_color_map_1_quant;
 836   cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */
 837   cquantize->odither[0] = NULL; /* Also flag odither arrays not allocated */
 838
 839   /* Make sure my internal arrays won't overflow */
 840   if (cinfo->out_color_components > MAX_Q_COMPS)
 841     ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);
 842   /* Make sure colormap indexes can be represented by JSAMPLEs */
 843   if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))
 844     ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1);
 845
 846   /* Create the colormap and color index table. */
 847   create_colormap(cinfo);
 848   create_colorindex(cinfo);
 849
 850   /* Allocate Floyd-Steinberg workspace now if requested.
 851    * We do this now since it is FAR storage and may affect the memory
 852    * manager's space calculations.  If the user changes to FS dither
 853    * mode in a later pass, we will allocate the space then, and will
 854    * possibly overrun the max_memory_to_use setting.
 855    */
 856   if (cinfo->dither_mode == JDITHER_FS)
 857     alloc_fs_workspace(cinfo);
 858 }
 859
 860 #endif /* QUANT_1PASS_SUPPORTED */