media/libjpeg/jquant1.c

   1 /*
   2  * jquant1.c
   3  *
   4  * This file was part of the Independent JPEG Group's software:
   5  * Copyright (C) 1991-1996, Thomas G. Lane.
   6  * libjpeg-turbo Modifications:
   7  * Copyright (C) 2009, 2015, D. R. Commander.
   8  * For conditions of distribution and use, see the accompanying README.ijg
   9  * file.
  10  *
  11  * This file contains 1-pass color quantization (color mapping) routines.
  12  * These routines provide mapping to a fixed color map using equally spaced
  13  * color values.  Optional Floyd-Steinberg or ordered dithering is available.
  14  */
  15
  16 #define JPEG_INTERNALS
  17 #include "jinclude.h"
  18 #include "jpeglib.h"
  19
  20 #ifdef QUANT_1PASS_SUPPORTED
  21
  22
  23 /*
  24  * The main purpose of 1-pass quantization is to provide a fast, if not very
  25  * high quality, colormapped output capability.  A 2-pass quantizer usually
  26  * gives better visual quality; however, for quantized grayscale output this
  27  * quantizer is perfectly adequate.  Dithering is highly recommended with this
  28  * quantizer, though you can turn it off if you really want to.
  29  *
  30  * In 1-pass quantization the colormap must be chosen in advance of seeing the
  31  * image.  We use a map consisting of all combinations of Ncolors[i] color
  32  * values for the i'th component.  The Ncolors[] values are chosen so that
  33  * their product, the total number of colors, is no more than that requested.
  34  * (In most cases, the product will be somewhat less.)
  35  *
  36  * Since the colormap is orthogonal, the representative value for each color
  37  * component can be determined without considering the other components;
  38  * then these indexes can be combined into a colormap index by a standard
  39  * N-dimensional-array-subscript calculation.  Most of the arithmetic involved
  40  * can be precalculated and stored in the lookup table colorindex[].
  41  * colorindex[i][j] maps pixel value j in component i to the nearest
  42  * representative value (grid plane) for that component; this index is
  43  * multiplied by the array stride for component i, so that the
  44  * index of the colormap entry closest to a given pixel value is just
  45  *    sum( colorindex[component-number][pixel-component-value] )
  46  * Aside from being fast, this scheme allows for variable spacing between
  47  * representative values with no additional lookup cost.
  48  *
  49  * If gamma correction has been applied in color conversion, it might be wise
  50  * to adjust the color grid spacing so that the representative colors are
  51  * equidistant in linear space.  At this writing, gamma correction is not
  52  * implemented by jdcolor, so nothing is done here.
  53  */
  54
  55
  56 /* Declarations for ordered dithering.
  57  *
  58  * We use a standard 16x16 ordered dither array.  The basic concept of ordered
  59  * dithering is described in many references, for instance Dale Schumacher's
  60  * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
  61  * In place of Schumacher's comparisons against a "threshold" value, we add a
  62  * "dither" value to the input pixel and then round the result to the nearest
  63  * output value.  The dither value is equivalent to (0.5 - threshold) times
  64  * the distance between output values.  For ordered dithering, we assume that
  65  * the output colors are equally spaced; if not, results will probably be
  66  * worse, since the dither may be too much or too little at a given point.
  67  *
  68  * The normal calculation would be to form pixel value + dither, range-limit
  69  * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.
  70  * We can skip the separate range-limiting step by extending the colorindex
  71  * table in both directions.
  72  */
  73
  74 #define ODITHER_SIZE  16        /* dimension of dither matrix */
  75 /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
  76 #define ODITHER_CELLS  (ODITHER_SIZE * ODITHER_SIZE) /* # cells in matrix */
  77 #define ODITHER_MASK  (ODITHER_SIZE - 1) /* mask for wrapping around
  78                                             counters */
  79
  80 typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
  81 typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];
  82
  83 static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {
  84   /* Bayer's order-4 dither array.  Generated by the code given in
  85    * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
  86    * The values in this array must range from 0 to ODITHER_CELLS-1.
  87    */
  88   {   0,192, 48,240, 12,204, 60,252,  3,195, 51,243, 15,207, 63,255 },
  89   { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },
  90   {  32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },
  91   { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },
  92   {   8,200, 56,248,  4,196, 52,244, 11,203, 59,251,  7,199, 55,247 },
  93   { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },
  94   {  40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },
  95   { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },
  96   {   2,194, 50,242, 14,206, 62,254,  1,193, 49,241, 13,205, 61,253 },
  97   { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },
  98   {  34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },
  99   { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },
 100   {  10,202, 58,250,  6,198, 54,246,  9,201, 57,249,  5,197, 53,245 },
 101   { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },
 102   {  42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },
 103   { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }
 104 };
 105
 106
 107 /* Declarations for Floyd-Steinberg dithering.
 108  *
 109  * Errors are accumulated into the array fserrors[], at a resolution of
 110  * 1/16th of a pixel count.  The error at a given pixel is propagated
 111  * to its not-yet-processed neighbors using the standard F-S fractions,
 112  *              ...     (here)  7/16
 113  *              3/16    5/16    1/16
 114  * We work left-to-right on even rows, right-to-left on odd rows.
 115  *
 116  * We can get away with a single array (holding one row's worth of errors)
 117  * by using it to store the current row's errors at pixel columns not yet
 118  * processed, but the next row's errors at columns already processed.  We
 119  * need only a few extra variables to hold the errors immediately around the
 120  * current column.  (If we are lucky, those variables are in registers, but
 121  * even if not, they're probably cheaper to access than array elements are.)
 122  *
 123  * The fserrors[] array is indexed [component#][position].
 124  * We provide (#columns + 2) entries per component; the extra entry at each
 125  * end saves us from special-casing the first and last pixels.
 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 JLONG FSERROR;          /* may need more than 16 bits */
 133 typedef JLONG LOCFSERROR;       /* be sure calculation temps are big enough */
 134 #endif
 135
 136 typedef FSERROR *FSERRPTR;      /* pointer to error array */
 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 allocated 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)(((JLONG)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)(((JLONG)(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, total_colors,
 290              cquantize->Ncolors[0], cquantize->Ncolors[1],
 291              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   JLONG 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 * ((JLONG)(ncolors - 1));
 415   for (j = 0; j < ODITHER_SIZE; j++) {
 416     for (k = 0; k < ODITHER_SIZE; k++) {
 417       num = ((JLONG)(ODITHER_CELLS - 1 -
 418                      2 * ((int)base_dither_matrix[j][k]))) * 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 += colorindex[ci][*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  = colorindex0[*ptrin++];
 510       pixcode += colorindex1[*ptrin++];
 511       pixcode += colorindex2[*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 *)output_buf[row], (size_t)(width * sizeof(JSAMPLE)));
 538     row_index = cquantize->row_index;
 539     for (ci = 0; ci < nc; ci++) {
 540       input_ptr = input_buf[row] + ci;
 541       output_ptr = output_buf[row];
 542       colorindex_ci = cquantize->colorindex[ci];
 543       dither = cquantize->odither[ci][row_index];
 544       col_index = 0;
 545
 546       for (col = width; col > 0; col--) {
 547         /* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,
 548          * select output value, accumulate into output code for this pixel.
 549          * Range-limiting need not be done explicitly, as we have extended
 550          * the colorindex table to produce the right answers for out-of-range
 551          * inputs.  The maximum dither is +- MAXJSAMPLE; this sets the
 552          * required amount of padding.
 553          */
 554         *output_ptr +=
 555           colorindex_ci[*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  = colorindex0[(*input_ptr++) + dither0[col_index]];
 599       pixcode += colorindex1[(*input_ptr++) + dither1[col_index]];
 600       pixcode += colorindex2[(*input_ptr++) + dither2[col_index]];
 601       *output_ptr++ = (JSAMPLE)pixcode;
 602       col_index = (col_index + 1) & ODITHER_MASK;
 603     }
 604     row_index = (row_index + 1) & ODITHER_MASK;
 605     cquantize->row_index = row_index;
 606   }
 607 }
 608
 609
 610 METHODDEF(void)
 611 quantize_fs_dither(j_decompress_ptr cinfo, JSAMPARRAY input_buf,
 612                    JSAMPARRAY output_buf, int num_rows)
 613 /* General case, with Floyd-Steinberg dithering */
 614 {
 615   my_cquantize_ptr cquantize = (my_cquantize_ptr)cinfo->cquantize;
 616   register LOCFSERROR cur;      /* current error or pixel value */
 617   LOCFSERROR belowerr;          /* error for pixel below cur */
 618   LOCFSERROR bpreverr;          /* error for below/prev col */
 619   LOCFSERROR bnexterr;          /* error for below/next col */
 620   LOCFSERROR delta;
 621   register FSERRPTR errorptr;   /* => fserrors[] at column before current */
 622   register JSAMPROW input_ptr;
 623   register JSAMPROW output_ptr;
 624   JSAMPROW colorindex_ci;
 625   JSAMPROW colormap_ci;
 626   int pixcode;
 627   int nc = cinfo->out_color_components;
 628   int dir;                      /* 1 for left-to-right, -1 for right-to-left */
 629   int dirnc;                    /* dir * nc */
 630   int ci;
 631   int row;
 632   JDIMENSION col;
 633   JDIMENSION width = cinfo->output_width;
 634   JSAMPLE *range_limit = cinfo->sample_range_limit;
 635   SHIFT_TEMPS
 636
 637   for (row = 0; row < num_rows; row++) {
 638     /* Initialize output values to 0 so can process components separately */
 639     jzero_far((void *)output_buf[row], (size_t)(width * sizeof(JSAMPLE)));
 640     for (ci = 0; ci < nc; ci++) {
 641       input_ptr = input_buf[row] + ci;
 642       output_ptr = output_buf[row];
 643       if (cquantize->on_odd_row) {
 644         /* work right to left in this row */
 645         input_ptr += (width - 1) * nc; /* so point to rightmost pixel */
 646         output_ptr += width - 1;
 647         dir = -1;
 648         dirnc = -nc;
 649         errorptr = cquantize->fserrors[ci] + (width + 1); /* => entry after last column */
 650       } else {
 651         /* work left to right in this row */
 652         dir = 1;
 653         dirnc = nc;
 654         errorptr = cquantize->fserrors[ci]; /* => entry before first column */
 655       }
 656       colorindex_ci = cquantize->colorindex[ci];
 657       colormap_ci = cquantize->sv_colormap[ci];
 658       /* Preset error values: no error propagated to first pixel from left */
 659       cur = 0;
 660       /* and no error propagated to row below yet */
 661       belowerr = bpreverr = 0;
 662
 663       for (col = width; col > 0; col--) {
 664         /* cur holds the error propagated from the previous pixel on the
 665          * current line.  Add the error propagated from the previous line
 666          * to form the complete error correction term for this pixel, and
 667          * round the error term (which is expressed * 16) to an integer.
 668          * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
 669          * for either sign of the error value.
 670          * Note: errorptr points to *previous* column's array entry.
 671          */
 672         cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4);
 673         /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
 674          * The maximum error is +- MAXJSAMPLE; this sets the required size
 675          * of the range_limit array.
 676          */
 677         cur += *input_ptr;
 678         cur = range_limit[cur];
 679         /* Select output value, accumulate into output code for this pixel */
 680         pixcode = colorindex_ci[cur];
 681         *output_ptr += (JSAMPLE)pixcode;
 682         /* Compute actual representation error at this pixel */
 683         /* Note: we can do this even though we don't have the final */
 684         /* pixel code, because the colormap is orthogonal. */
 685         cur -= colormap_ci[pixcode];
 686         /* Compute error fractions to be propagated to adjacent pixels.
 687          * Add these into the running sums, and simultaneously shift the
 688          * next-line error sums left by 1 column.
 689          */
 690         bnexterr = cur;
 691         delta = cur * 2;
 692         cur += delta;           /* form error * 3 */
 693         errorptr[0] = (FSERROR)(bpreverr + cur);
 694         cur += delta;           /* form error * 5 */
 695         bpreverr = belowerr + cur;
 696         belowerr = bnexterr;
 697         cur += delta;           /* form error * 7 */
 698         /* At this point cur contains the 7/16 error value to be propagated
 699          * to the next pixel on the current line, and all the errors for the
 700          * next line have been shifted over. We are therefore ready to move on.
 701          */
 702         input_ptr += dirnc;     /* advance input ptr to next column */
 703         output_ptr += dir;      /* advance output ptr to next column */
 704         errorptr += dir;        /* advance errorptr to current column */
 705       }
 706       /* Post-loop cleanup: we must unload the final error value into the
 707        * final fserrors[] entry.  Note we need not unload belowerr because
 708        * it is for the dummy column before or after the actual array.
 709        */
 710       errorptr[0] = (FSERROR)bpreverr; /* unload prev err into array */
 711     }
 712     cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);
 713   }
 714 }
 715
 716
 717 /*
 718  * Allocate workspace for Floyd-Steinberg errors.
 719  */
 720
 721 LOCAL(void)
 722 alloc_fs_workspace(j_decompress_ptr cinfo)
 723 {
 724   my_cquantize_ptr cquantize = (my_cquantize_ptr)cinfo->cquantize;
 725   size_t arraysize;
 726   int i;
 727
 728   arraysize = (size_t)((cinfo->output_width + 2) * sizeof(FSERROR));
 729   for (i = 0; i < cinfo->out_color_components; i++) {
 730     cquantize->fserrors[i] = (FSERRPTR)
 731       (*cinfo->mem->alloc_large) ((j_common_ptr)cinfo, JPOOL_IMAGE, arraysize);
 732   }
 733 }
 734
 735
 736 /*
 737  * Initialize for one-pass color quantization.
 738  */
 739
 740 METHODDEF(void)
 741 start_pass_1_quant(j_decompress_ptr cinfo, boolean is_pre_scan)
 742 {
 743   my_cquantize_ptr cquantize = (my_cquantize_ptr)cinfo->cquantize;
 744   size_t arraysize;
 745   int i;
 746
 747   /* Install my colormap. */
 748   cinfo->colormap = cquantize->sv_colormap;
 749   cinfo->actual_number_of_colors = cquantize->sv_actual;
 750
 751   /* Initialize for desired dithering mode. */
 752   switch (cinfo->dither_mode) {
 753   case JDITHER_NONE:
 754     if (cinfo->out_color_components == 3)
 755       cquantize->pub.color_quantize = color_quantize3;
 756     else
 757       cquantize->pub.color_quantize = color_quantize;
 758     break;
 759   case JDITHER_ORDERED:
 760     if (cinfo->out_color_components == 3)
 761       cquantize->pub.color_quantize = quantize3_ord_dither;
 762     else
 763       cquantize->pub.color_quantize = quantize_ord_dither;
 764     cquantize->row_index = 0;   /* initialize state for ordered dither */
 765     /* If user changed to ordered dither from another mode,
 766      * we must recreate the color index table with padding.
 767      * This will cost extra space, but probably isn't very likely.
 768      */
 769     if (!cquantize->is_padded)
 770       create_colorindex(cinfo);
 771     /* Create ordered-dither tables if we didn't already. */
 772     if (cquantize->odither[0] == NULL)
 773       create_odither_tables(cinfo);
 774     break;
 775   case JDITHER_FS:
 776     cquantize->pub.color_quantize = quantize_fs_dither;
 777     cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */
 778     /* Allocate Floyd-Steinberg workspace if didn't already. */
 779     if (cquantize->fserrors[0] == NULL)
 780       alloc_fs_workspace(cinfo);
 781     /* Initialize the propagated errors to zero. */
 782     arraysize = (size_t)((cinfo->output_width + 2) * sizeof(FSERROR));
 783     for (i = 0; i < cinfo->out_color_components; i++)
 784       jzero_far((void *)cquantize->fserrors[i], arraysize);
 785     break;
 786   default:
 787     ERREXIT(cinfo, JERR_NOT_COMPILED);
 788     break;
 789   }
 790 }
 791
 792
 793 /*
 794  * Finish up at the end of the pass.
 795  */
 796
 797 METHODDEF(void)
 798 finish_pass_1_quant(j_decompress_ptr cinfo)
 799 {
 800   /* no work in 1-pass case */
 801 }
 802
 803
 804 /*
 805  * Switch to a new external colormap between output passes.
 806  * Shouldn't get to this module!
 807  */
 808
 809 METHODDEF(void)
 810 new_color_map_1_quant(j_decompress_ptr cinfo)
 811 {
 812   ERREXIT(cinfo, JERR_MODE_CHANGE);
 813 }
 814
 815
 816 /*
 817  * Module initialization routine for 1-pass color quantization.
 818  */
 819
 820 GLOBAL(void)
 821 jinit_1pass_quantizer(j_decompress_ptr cinfo)
 822 {
 823   my_cquantize_ptr cquantize;
 824
 825   cquantize = (my_cquantize_ptr)
 826     (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
 827                                 sizeof(my_cquantizer));
 828   cinfo->cquantize = (struct jpeg_color_quantizer *)cquantize;
 829   cquantize->pub.start_pass = start_pass_1_quant;
 830   cquantize->pub.finish_pass = finish_pass_1_quant;
 831   cquantize->pub.new_color_map = new_color_map_1_quant;
 832   cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */
 833   cquantize->odither[0] = NULL; /* Also flag odither arrays not allocated */
 834
 835   /* Make sure my internal arrays won't overflow */
 836   if (cinfo->out_color_components > MAX_Q_COMPS)
 837     ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);
 838   /* Make sure colormap indexes can be represented by JSAMPLEs */
 839   if (cinfo->desired_number_of_colors > (MAXJSAMPLE + 1))
 840     ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE + 1);
 841
 842   /* Create the colormap and color index table. */
 843   create_colormap(cinfo);
 844   create_colorindex(cinfo);
 845
 846   /* Allocate Floyd-Steinberg workspace now if requested.
 847    * We do this now since it may affect the memory manager's space
 848    * calculations.  If the user changes to FS dither mode in a later pass, we
 849    * will allocate the space then, and will possibly overrun the
 850    * max_memory_to_use setting.
 851    */
 852   if (cinfo->dither_mode == JDITHER_FS)
 853     alloc_fs_workspace(cinfo);
 854 }
 855
 856 #endif /* QUANT_1PASS_SUPPORTED */