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.
8 * This file contains 1-pass color quantization (color mapping) routines.
9 * These routines provide mapping to a fixed color map using equally spaced
10 * color values. Optional Floyd-Steinberg or ordered dithering is available.
13 #define JPEG_INTERNALS
17 #ifdef QUANT_1PASS_SUPPORTED
21 * The main purpose of 1-pass quantization is to provide a fast, if not very
22 * high quality, colormapped output capability. A 2-pass quantizer usually
23 * gives better visual quality; however, for quantized grayscale output this
24 * quantizer is perfectly adequate. Dithering is highly recommended with this
25 * quantizer, though you can turn it off if you really want to.
27 * In 1-pass quantization the colormap must be chosen in advance of seeing the
28 * image. We use a map consisting of all combinations of Ncolors[i] color
29 * values for the i'th component. The Ncolors[] values are chosen so that
30 * their product, the total number of colors, is no more than that requested.
31 * (In most cases, the product will be somewhat less.)
33 * Since the colormap is orthogonal, the representative value for each color
34 * component can be determined without considering the other components;
35 * then these indexes can be combined into a colormap index by a standard
36 * N-dimensional-array-subscript calculation. Most of the arithmetic involved
37 * can be precalculated and stored in the lookup table colorindex[].
38 * colorindex[i][j] maps pixel value j in component i to the nearest
39 * representative value (grid plane) for that component; this index is
40 * multiplied by the array stride for component i, so that the
41 * index of the colormap entry closest to a given pixel value is just
42 * sum( colorindex[component-number][pixel-component-value] )
43 * Aside from being fast, this scheme allows for variable spacing between
44 * representative values with no additional lookup cost.
46 * If gamma correction has been applied in color conversion, it might be wise
47 * to adjust the color grid spacing so that the representative colors are
48 * equidistant in linear space. At this writing, gamma correction is not
49 * implemented by jdcolor, so nothing is done here.
53 /* Declarations for ordered dithering.
55 * We use a standard 16x16 ordered dither array. The basic concept of ordered
56 * dithering is described in many references, for instance Dale Schumacher's
57 * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
58 * In place of Schumacher's comparisons against a "threshold" value, we add a
59 * "dither" value to the input pixel and then round the result to the nearest
60 * output value. The dither value is equivalent to (0.5 - threshold) times
61 * the distance between output values. For ordered dithering, we assume that
62 * the output colors are equally spaced; if not, results will probably be
63 * worse, since the dither may be too much or too little at a given point.
65 * The normal calculation would be to form pixel value + dither, range-limit
66 * this to 0..MAXJSAMPLE, and then index into the colorindex table as usual.
67 * We can skip the separate range-limiting step by extending the colorindex
68 * table in both directions.
71 #define ODITHER_SIZE 16 /* dimension of dither matrix */
72 /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
73 #define ODITHER_CELLS (ODITHER_SIZE*ODITHER_SIZE) /* # cells in matrix */
74 #define ODITHER_MASK (ODITHER_SIZE-1) /* mask for wrapping around counters */
76 typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
77 typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];
79 static const UINT8 base_dither_matrix[ODITHER_SIZE][ODITHER_SIZE] = {
80 /* Bayer's order-4 dither array. Generated by the code given in
81 * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
82 * The values in this array must range from 0 to ODITHER_CELLS-1.
84 { 0,192, 48,240, 12,204, 60,252, 3,195, 51,243, 15,207, 63,255 },
85 { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },
86 { 32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },
87 { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },
88 { 8,200, 56,248, 4,196, 52,244, 11,203, 59,251, 7,199, 55,247 },
89 { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },
90 { 40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },
91 { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },
92 { 2,194, 50,242, 14,206, 62,254, 1,193, 49,241, 13,205, 61,253 },
93 { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },
94 { 34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },
95 { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },
96 { 10,202, 58,250, 6,198, 54,246, 9,201, 57,249, 5,197, 53,245 },
97 { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },
98 { 42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },
99 { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }
103 /* Declarations for Floyd-Steinberg dithering.
105 * Errors are accumulated into the array fserrors[], at a resolution of
106 * 1/16th of a pixel count. The error at a given pixel is propagated
107 * to its not-yet-processed neighbors using the standard F-S fractions,
110 * We work left-to-right on even rows, right-to-left on odd rows.
112 * We can get away with a single array (holding one row's worth of errors)
113 * by using it to store the current row's errors at pixel columns not yet
114 * processed, but the next row's errors at columns already processed. We
115 * need only a few extra variables to hold the errors immediately around the
116 * current column. (If we are lucky, those variables are in registers, but
117 * even if not, they're probably cheaper to access than array elements are.)
119 * The fserrors[] array is indexed [component#][position].
120 * We provide (#columns + 2) entries per component; the extra entry at each
121 * end saves us from special-casing the first and last pixels.
123 * Note: on a wide image, we might not have enough room in a PC's near data
124 * segment to hold the error array; so it is allocated with alloc_large.
127 #if BITS_IN_JSAMPLE == 8
128 typedef INT16 FSERROR; /* 16 bits should be enough */
129 typedef int LOCFSERROR; /* use 'int' for calculation temps */
131 typedef INT32 FSERROR; /* may need more than 16 bits */
132 typedef INT32 LOCFSERROR; /* be sure calculation temps are big enough */
135 typedef FSERROR FAR *FSERRPTR; /* pointer to error array (in FAR storage!) */
138 /* Private subobject */
140 #define MAX_Q_COMPS 4 /* max components I can handle */
143 struct jpeg_color_quantizer pub; /* public fields */
145 /* Initially allocated colormap is saved here */
146 JSAMPARRAY sv_colormap; /* The color map as a 2-D pixel array */
147 int sv_actual; /* number of entries in use */
149 JSAMPARRAY colorindex; /* Precomputed mapping for speed */
150 /* colorindex[i][j] = index of color closest to pixel value j in component i,
151 * premultiplied as described above. Since colormap indexes must fit into
152 * JSAMPLEs, the entries of this array will too.
154 boolean is_padded; /* is the colorindex padded for odither? */
156 int Ncolors[MAX_Q_COMPS]; /* # of values alloced to each component */
158 /* Variables for ordered dithering */
159 int row_index; /* cur row's vertical index in dither matrix */
160 ODITHER_MATRIX_PTR odither[MAX_Q_COMPS]; /* one dither array per component */
162 /* Variables for Floyd-Steinberg dithering */
163 FSERRPTR fserrors[MAX_Q_COMPS]; /* accumulated errors */
164 boolean on_odd_row; /* flag to remember which row we are on */
167 typedef my_cquantizer * my_cquantize_ptr;
171 * Policy-making subroutines for create_colormap and create_colorindex.
172 * These routines determine the colormap to be used. The rest of the module
173 * only assumes that the colormap is orthogonal.
175 * * select_ncolors decides how to divvy up the available colors
176 * among the components.
177 * * output_value defines the set of representative values for a component.
178 * * largest_input_value defines the mapping from input values to
179 * representative values for a component.
180 * Note that the latter two routines may impose different policies for
181 * different components, though this is not currently done.
186 select_ncolors (j_decompress_ptr cinfo, int Ncolors[])
187 /* Determine allocation of desired colors to components, */
188 /* and fill in Ncolors[] array to indicate choice. */
189 /* Return value is total number of colors (product of Ncolors[] values). */
191 int nc = cinfo->out_color_components; /* number of color components */
192 int max_colors = cinfo->desired_number_of_colors;
193 int total_colors, iroot, i, j;
196 static const int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE };
198 /* We can allocate at least the nc'th root of max_colors per component. */
199 /* Compute floor(nc'th root of max_colors). */
203 temp = iroot; /* set temp = iroot ** nc */
204 for (i = 1; i < nc; i++)
206 } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */
207 iroot--; /* now iroot = floor(root) */
209 /* Must have at least 2 color values per component */
211 ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp);
213 /* Initialize to iroot color values for each component */
215 for (i = 0; i < nc; i++) {
217 total_colors *= iroot;
219 /* We may be able to increment the count for one or more components without
220 * exceeding max_colors, though we know not all can be incremented.
221 * Sometimes, the first component can be incremented more than once!
222 * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)
223 * In RGB colorspace, try to increment G first, then R, then B.
227 for (i = 0; i < nc; i++) {
228 j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i);
229 /* calculate new total_colors if Ncolors[j] is incremented */
230 temp = total_colors / Ncolors[j];
231 temp *= Ncolors[j]+1; /* done in long arith to avoid oflo */
232 if (temp > (long) max_colors)
233 break; /* won't fit, done with this pass */
234 Ncolors[j]++; /* OK, apply the increment */
235 total_colors = (int) temp;
245 output_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
246 /* Return j'th output value, where j will range from 0 to maxj */
247 /* The output values must fall in 0..MAXJSAMPLE in increasing order */
251 /* We always provide values 0 and MAXJSAMPLE for each component;
252 * any additional values are equally spaced between these limits.
253 * (Forcing the upper and lower values to the limits ensures that
254 * dithering can't produce a color outside the selected gamut.)
256 return (int) (((INT32) j * MAXJSAMPLE + maxj/2) / maxj);
261 largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
262 /* Return largest input value that should map to j'th output value */
263 /* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */
267 /* Breakpoints are halfway between values returned by output_value */
268 return (int) (((INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj));
273 * Create the colormap.
277 create_colormap (j_decompress_ptr cinfo)
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;
284 /* Select number of colors for each component */
285 total_colors = select_ncolors(cinfo, cquantize->Ncolors);
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]);
293 TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors);
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. */
299 colormap = (*cinfo->mem->alloc_sarray)
300 ((j_common_ptr) cinfo, JPOOL_IMAGE,
301 (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components);
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;
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;
321 blkdist = blksize; /* blksize of this color is blkdist of next */
324 /* Save the colormap in private storage,
325 * where it will survive color quantization mode changes.
327 cquantize->sv_colormap = colormap;
328 cquantize->sv_actual = total_colors;
333 * Create the color index table.
337 create_colorindex (j_decompress_ptr cinfo)
339 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
341 int i,j,k, nci, blksize, val, pad;
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.
348 if (cinfo->dither_mode == JDITHER_ORDERED) {
350 cquantize->is_padded = TRUE;
353 cquantize->is_padded = FALSE;
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);
361 /* blksize is number of adjacent repeated entries for a component */
362 blksize = cquantize->sv_actual;
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;
369 /* adjust colorindex pointers to provide padding at negative indexes. */
371 cquantize->colorindex[i] += MAXJSAMPLE;
373 /* in loop, val = index of current output value, */
374 /* and k = largest j that maps to current val */
375 indexptr = cquantize->colorindex[i];
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);
384 /* Pad at both ends if necessary */
386 for (j = 1; j <= MAXJSAMPLE; j++) {
387 indexptr[-j] = indexptr[0];
388 indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE];
395 * Create an ordered-dither array for a component having ncolors
396 * distinct output values.
399 LOCAL(ODITHER_MATRIX_PTR)
400 make_odither_array (j_decompress_ptr cinfo, int ncolors)
402 ODITHER_MATRIX_PTR odither;
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.
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])))
419 /* Ensure round towards zero despite C's lack of consistency
420 * about rounding negative values in integer division...
422 odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den);
430 * Create the ordered-dither tables.
431 * Components having the same number of representative colors may
432 * share a dither table.
436 create_odither_tables (j_decompress_ptr cinfo)
438 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
439 ODITHER_MATRIX_PTR odither;
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];
451 if (odither == NULL) /* need a new table? */
452 odither = make_odither_array(cinfo, nci);
453 cquantize->odither[i] = odither;
459 * Map some rows of pixels to the output colormapped representation.
463 color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
464 JSAMPARRAY output_buf, int num_rows)
465 /* General case, no dithering */
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;
473 JDIMENSION width = cinfo->output_width;
474 register int nc = cinfo->out_color_components;
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--) {
481 for (ci = 0; ci < nc; ci++) {
482 pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]);
484 *ptrout++ = (JSAMPLE) pixcode;
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 */
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];
503 JDIMENSION width = cinfo->output_width;
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;
519 quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
520 JSAMPARRAY output_buf, int num_rows)
521 /* General case, with ordered dithering */
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;
533 JDIMENSION width = cinfo->output_width;
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];
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.
555 *output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]];
558 col_index = (col_index + 1) & ODITHER_MASK;
561 /* Advance row index for next row */
562 row_index = (row_index + 1) & ODITHER_MASK;
563 cquantize->row_index = row_index;
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 */
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 */
583 int row_index, col_index; /* current indexes into dither matrix */
586 JDIMENSION width = cinfo->output_width;
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];
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;
607 row_index = (row_index + 1) & ODITHER_MASK;
608 cquantize->row_index = row_index;
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 */
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 */
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;
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 */
636 JDIMENSION width = cinfo->output_width;
637 JSAMPLE *range_limit = cinfo->sample_range_limit;
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;
653 errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */
655 /* work left to right in this row */
658 errorptr = cquantize->fserrors[ci]; /* => entry before first column */
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 */
664 /* and no error propagated to row below yet */
665 belowerr = bpreverr = 0;
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.
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.
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.
696 cur += delta; /* form error * 3 */
697 errorptr[0] = (FSERROR) (bpreverr + cur);
698 cur += delta; /* form error * 5 */
699 bpreverr = belowerr + cur;
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.
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 */
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.
714 errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */
716 cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);
722 * Allocate workspace for Floyd-Steinberg errors.
726 alloc_fs_workspace (j_decompress_ptr cinfo)
728 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
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);
741 * Initialize for one-pass color quantization.
745 start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan)
747 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
752 /* Install my colormap. */
753 cinfo->colormap = cquantize->sv_colormap;
754 cinfo->actual_number_of_colors = cquantize->sv_actual;
756 /* Initialize for desired dithering mode. */
757 switch (cinfo->dither_mode) {
759 if (cinfo->out_color_components == 3)
760 cquantize->pub.color_quantize = color_quantize3;
762 cquantize->pub.color_quantize = color_quantize;
764 case JDITHER_ORDERED:
765 if (cinfo->out_color_components == 3)
766 cquantize->pub.color_quantize = quantize3_ord_dither;
768 cquantize->pub.color_quantize = quantize_ord_dither;
769 cquantize->row_index = 0; /* initialize state for ordered dither */
770 /* If user changed to ordered dither from another mode,
771 * we must recreate the color index table with padding.
772 * This will cost extra space, but probably isn't very likely.
774 if (! cquantize->is_padded)
775 create_colorindex(cinfo);
776 /* Create ordered-dither tables if we didn't already. */
777 if (cquantize->odither[0] == NULL)
778 create_odither_tables(cinfo);
781 cquantize->pub.color_quantize = quantize_fs_dither;
782 cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */
783 /* Allocate Floyd-Steinberg workspace if didn't already. */
784 if (cquantize->fserrors[0] == NULL)
785 alloc_fs_workspace(cinfo);
786 /* Initialize the propagated errors to zero. */
787 arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
788 for (i = 0; i < cinfo->out_color_components; i++)
789 jzero_far((void FAR *) cquantize->fserrors[i], arraysize);
792 ERREXIT(cinfo, JERR_NOT_COMPILED);
799 * Finish up at the end of the pass.
803 finish_pass_1_quant (j_decompress_ptr cinfo)
806 /* no work in 1-pass case */
811 * Switch to a new external colormap between output passes.
812 * Shouldn't get to this module!
816 new_color_map_1_quant (j_decompress_ptr cinfo)
818 ERREXIT(cinfo, JERR_MODE_CHANGE);
823 * Module initialization routine for 1-pass color quantization.
827 jinit_1pass_quantizer (j_decompress_ptr cinfo)
829 my_cquantize_ptr cquantize;
831 cquantize = (my_cquantize_ptr)
832 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
833 SIZEOF(my_cquantizer));
834 cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;
835 cquantize->pub.start_pass = start_pass_1_quant;
836 cquantize->pub.finish_pass = finish_pass_1_quant;
837 cquantize->pub.new_color_map = new_color_map_1_quant;
838 cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */
839 cquantize->odither[0] = NULL; /* Also flag odither arrays not allocated */
841 /* Make sure my internal arrays won't overflow */
842 if (cinfo->out_color_components > MAX_Q_COMPS)
843 ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);
844 /* Make sure colormap indexes can be represented by JSAMPLEs */
845 if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))
846 ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1);
848 /* Create the colormap and color index table. */
849 create_colormap(cinfo);
850 create_colorindex(cinfo);
852 /* Allocate Floyd-Steinberg workspace now if requested.
853 * We do this now since it is FAR storage and may affect the memory
854 * manager's space calculations. If the user changes to FS dither
855 * mode in a later pass, we will allocate the space then, and will
856 * possibly overrun the max_memory_to_use setting.
858 if (cinfo->dither_mode == JDITHER_FS)
859 alloc_fs_workspace(cinfo);
862 #endif /* QUANT_1PASS_SUPPORTED */