1/*
2 * jquant1.c
3 *
4 * Copyright (C) 1991-1996, Thomas G. Lane.
5 * Modified 2011 by Guido Vollbeding.
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
77typedef int ODITHER_MATRIX[ODITHER_SIZE][ODITHER_SIZE];
78typedef int (*ODITHER_MATRIX_PTR)[ODITHER_SIZE];
79
80static 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
129typedef INT16 FSERROR; /* 16 bits should be enough */
130typedef int LOCFSERROR; /* use 'int' for calculation temps */
131#else
132typedef INT32 FSERROR; /* may need more than 16 bits */
133typedef INT32 LOCFSERROR; /* be sure calculation temps are big enough */
134#endif
135
136typedef 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
143typedef 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
168typedef 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
186LOCAL(int)
187select_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 static const int RGB_order[3] = { RGB_GREEN, RGB_RED, RGB_BLUE };
198
199 /* We can allocate at least the nc'th root of max_colors per component. */
200 /* Compute floor(nc'th root of max_colors). */
201 iroot = 1;
202 do {
203 iroot++;
204 temp = iroot; /* set temp = iroot ** nc */
205 for (i = 1; i < nc; i++)
206 temp *= iroot;
207 } while (temp <= (long) max_colors); /* repeat till iroot exceeds root */
208 iroot--; /* now iroot = floor(root) */
209
210 /* Must have at least 2 color values per component */
211 if (iroot < 2)
212 ERREXIT1(cinfo, JERR_QUANT_FEW_COLORS, (int) temp);
213
214 /* Initialize to iroot color values for each component */
215 total_colors = 1;
216 for (i = 0; i < nc; i++) {
217 Ncolors[i] = iroot;
218 total_colors *= iroot;
219 }
220 /* We may be able to increment the count for one or more components without
221 * exceeding max_colors, though we know not all can be incremented.
222 * Sometimes, the first component can be incremented more than once!
223 * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)
224 * In RGB colorspace, try to increment G first, then R, then B.
225 */
226 do {
227 changed = FALSE;
228 for (i = 0; i < nc; i++) {
229 j = (cinfo->out_color_space == JCS_RGB ? RGB_order[i] : i);
230 /* calculate new total_colors if Ncolors[j] is incremented */
231 temp = total_colors / Ncolors[j];
232 temp *= Ncolors[j]+1; /* done in long arith to avoid oflo */
233 if (temp > (long) max_colors)
234 break; /* won't fit, done with this pass */
235 Ncolors[j]++; /* OK, apply the increment */
236 total_colors = (int) temp;
237 changed = TRUE;
238 }
239 } while (changed);
240
241 return total_colors;
242}
243
244
245LOCAL(int)
246output_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
247/* Return j'th output value, where j will range from 0 to maxj */
248/* The output values must fall in 0..MAXJSAMPLE in increasing order */
249{
250 /* We always provide values 0 and MAXJSAMPLE for each component;
251 * any additional values are equally spaced between these limits.
252 * (Forcing the upper and lower values to the limits ensures that
253 * dithering can't produce a color outside the selected gamut.)
254 */
255 return (int) (((INT32) j * MAXJSAMPLE + maxj/2) / maxj);
256}
257
258
259LOCAL(int)
260largest_input_value (j_decompress_ptr cinfo, int ci, int j, int maxj)
261/* Return largest input value that should map to j'th output value */
262/* Must have largest(j=0) >= 0, and largest(j=maxj) >= MAXJSAMPLE */
263{
264 /* Breakpoints are halfway between values returned by output_value */
265 return (int) (((INT32) (2*j + 1) * MAXJSAMPLE + maxj) / (2*maxj));
266}
267
268
269/*
270 * Create the colormap.
271 */
272
273LOCAL(void)
274create_colormap (j_decompress_ptr cinfo)
275{
276 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
277 JSAMPARRAY colormap; /* Created colormap */
278 int total_colors; /* Number of distinct output colors */
279 int i,j,k, nci, blksize, blkdist, ptr, val;
280
281 /* Select number of colors for each component */
282 total_colors = select_ncolors(cinfo, cquantize->Ncolors);
283
284 /* Report selected color counts */
285 if (cinfo->out_color_components == 3)
286 TRACEMS4(cinfo, 1, JTRC_QUANT_3_NCOLORS,
287 total_colors, cquantize->Ncolors[0],
288 cquantize->Ncolors[1], cquantize->Ncolors[2]);
289 else
290 TRACEMS1(cinfo, 1, JTRC_QUANT_NCOLORS, total_colors);
291
292 /* Allocate and fill in the colormap. */
293 /* The colors are ordered in the map in standard row-major order, */
294 /* i.e. rightmost (highest-indexed) color changes most rapidly. */
295
296 colormap = (*cinfo->mem->alloc_sarray)
297 ((j_common_ptr) cinfo, JPOOL_IMAGE,
298 (JDIMENSION) total_colors, (JDIMENSION) cinfo->out_color_components);
299
300 /* blksize is number of adjacent repeated entries for a component */
301 /* blkdist is distance between groups of identical entries for a component */
302 blkdist = total_colors;
303
304 for (i = 0; i < cinfo->out_color_components; i++) {
305 /* fill in colormap entries for i'th color component */
306 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
307 blksize = blkdist / nci;
308 for (j = 0; j < nci; j++) {
309 /* Compute j'th output value (out of nci) for component */
310 val = output_value(cinfo, i, j, nci-1);
311 /* Fill in all colormap entries that have this value of this component */
312 for (ptr = j * blksize; ptr < total_colors; ptr += blkdist) {
313 /* fill in blksize entries beginning at ptr */
314 for (k = 0; k < blksize; k++)
315 colormap[i][ptr+k] = (JSAMPLE) val;
316 }
317 }
318 blkdist = blksize; /* blksize of this color is blkdist of next */
319 }
320
321 /* Save the colormap in private storage,
322 * where it will survive color quantization mode changes.
323 */
324 cquantize->sv_colormap = colormap;
325 cquantize->sv_actual = total_colors;
326}
327
328
329/*
330 * Create the color index table.
331 */
332
333LOCAL(void)
334create_colorindex (j_decompress_ptr cinfo)
335{
336 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
337 JSAMPROW indexptr;
338 int i,j,k, nci, blksize, val, pad;
339
340 /* For ordered dither, we pad the color index tables by MAXJSAMPLE in
341 * each direction (input index values can be -MAXJSAMPLE .. 2*MAXJSAMPLE).
342 * This is not necessary in the other dithering modes. However, we
343 * flag whether it was done in case user changes dithering mode.
344 */
345 if (cinfo->dither_mode == JDITHER_ORDERED) {
346 pad = MAXJSAMPLE*2;
347 cquantize->is_padded = TRUE;
348 } else {
349 pad = 0;
350 cquantize->is_padded = FALSE;
351 }
352
353 cquantize->colorindex = (*cinfo->mem->alloc_sarray)
354 ((j_common_ptr) cinfo, JPOOL_IMAGE,
355 (JDIMENSION) (MAXJSAMPLE+1 + pad),
356 (JDIMENSION) cinfo->out_color_components);
357
358 /* blksize is number of adjacent repeated entries for a component */
359 blksize = cquantize->sv_actual;
360
361 for (i = 0; i < cinfo->out_color_components; i++) {
362 /* fill in colorindex entries for i'th color component */
363 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
364 blksize = blksize / nci;
365
366 /* adjust colorindex pointers to provide padding at negative indexes. */
367 if (pad)
368 cquantize->colorindex[i] += MAXJSAMPLE;
369
370 /* in loop, val = index of current output value, */
371 /* and k = largest j that maps to current val */
372 indexptr = cquantize->colorindex[i];
373 val = 0;
374 k = largest_input_value(cinfo, i, 0, nci-1);
375 for (j = 0; j <= MAXJSAMPLE; j++) {
376 while (j > k) /* advance val if past boundary */
377 k = largest_input_value(cinfo, i, ++val, nci-1);
378 /* premultiply so that no multiplication needed in main processing */
379 indexptr[j] = (JSAMPLE) (val * blksize);
380 }
381 /* Pad at both ends if necessary */
382 if (pad)
383 for (j = 1; j <= MAXJSAMPLE; j++) {
384 indexptr[-j] = indexptr[0];
385 indexptr[MAXJSAMPLE+j] = indexptr[MAXJSAMPLE];
386 }
387 }
388}
389
390
391/*
392 * Create an ordered-dither array for a component having ncolors
393 * distinct output values.
394 */
395
396LOCAL(ODITHER_MATRIX_PTR)
397make_odither_array (j_decompress_ptr cinfo, int ncolors)
398{
399 ODITHER_MATRIX_PTR odither;
400 int j,k;
401 INT32 num,den;
402
403 odither = (ODITHER_MATRIX_PTR)
404 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
405 SIZEOF(ODITHER_MATRIX));
406 /* The inter-value distance for this color is MAXJSAMPLE/(ncolors-1).
407 * Hence the dither value for the matrix cell with fill order f
408 * (f=0..N-1) should be (N-1-2*f)/(2*N) * MAXJSAMPLE/(ncolors-1).
409 * On 16-bit-int machine, be careful to avoid overflow.
410 */
411 den = 2 * ODITHER_CELLS * ((INT32) (ncolors - 1));
412 for (j = 0; j < ODITHER_SIZE; j++) {
413 for (k = 0; k < ODITHER_SIZE; k++) {
414 num = ((INT32) (ODITHER_CELLS-1 - 2*((int)base_dither_matrix[j][k])))
415 * MAXJSAMPLE;
416 /* Ensure round towards zero despite C's lack of consistency
417 * about rounding negative values in integer division...
418 */
419 odither[j][k] = (int) (num<0 ? -((-num)/den) : num/den);
420 }
421 }
422 return odither;
423}
424
425
426/*
427 * Create the ordered-dither tables.
428 * Components having the same number of representative colors may
429 * share a dither table.
430 */
431
432LOCAL(void)
433create_odither_tables (j_decompress_ptr cinfo)
434{
435 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
436 ODITHER_MATRIX_PTR odither;
437 int i, j, nci;
438
439 for (i = 0; i < cinfo->out_color_components; i++) {
440 nci = cquantize->Ncolors[i]; /* # of distinct values for this color */
441 odither = NULL; /* search for matching prior component */
442 for (j = 0; j < i; j++) {
443 if (nci == cquantize->Ncolors[j]) {
444 odither = cquantize->odither[j];
445 break;
446 }
447 }
448 if (odither == NULL) /* need a new table? */
449 odither = make_odither_array(cinfo, nci);
450 cquantize->odither[i] = odither;
451 }
452}
453
454
455/*
456 * Map some rows of pixels to the output colormapped representation.
457 */
458
459METHODDEF(void)
460color_quantize (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
461 JSAMPARRAY output_buf, int num_rows)
462/* General case, no dithering */
463{
464 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
465 JSAMPARRAY colorindex = cquantize->colorindex;
466 register int pixcode, ci;
467 register JSAMPROW ptrin, ptrout;
468 int row;
469 JDIMENSION col;
470 JDIMENSION width = cinfo->output_width;
471 register int nc = cinfo->out_color_components;
472
473 for (row = 0; row < num_rows; row++) {
474 ptrin = input_buf[row];
475 ptrout = output_buf[row];
476 for (col = width; col > 0; col--) {
477 pixcode = 0;
478 for (ci = 0; ci < nc; ci++) {
479 pixcode += GETJSAMPLE(colorindex[ci][GETJSAMPLE(*ptrin++)]);
480 }
481 *ptrout++ = (JSAMPLE) pixcode;
482 }
483 }
484}
485
486
487METHODDEF(void)
488color_quantize3 (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
489 JSAMPARRAY output_buf, int num_rows)
490/* Fast path for out_color_components==3, no dithering */
491{
492 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
493 register int pixcode;
494 register JSAMPROW ptrin, ptrout;
495 JSAMPROW colorindex0 = cquantize->colorindex[0];
496 JSAMPROW colorindex1 = cquantize->colorindex[1];
497 JSAMPROW colorindex2 = cquantize->colorindex[2];
498 int row;
499 JDIMENSION col;
500 JDIMENSION width = cinfo->output_width;
501
502 for (row = 0; row < num_rows; row++) {
503 ptrin = input_buf[row];
504 ptrout = output_buf[row];
505 for (col = width; col > 0; col--) {
506 pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*ptrin++)]);
507 pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*ptrin++)]);
508 pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*ptrin++)]);
509 *ptrout++ = (JSAMPLE) pixcode;
510 }
511 }
512}
513
514
515METHODDEF(void)
516quantize_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
517 JSAMPARRAY output_buf, int num_rows)
518/* General case, with ordered dithering */
519{
520 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
521 register JSAMPROW input_ptr;
522 register JSAMPROW output_ptr;
523 JSAMPROW colorindex_ci;
524 int * dither; /* points to active row of dither matrix */
525 int row_index, col_index; /* current indexes into dither matrix */
526 int nc = cinfo->out_color_components;
527 int ci;
528 int row;
529 JDIMENSION col;
530 JDIMENSION width = cinfo->output_width;
531
532 for (row = 0; row < num_rows; row++) {
533 /* Initialize output values to 0 so can process components separately */
534 FMEMZERO((void FAR *) output_buf[row],
535 (size_t) (width * SIZEOF(JSAMPLE)));
536 row_index = cquantize->row_index;
537 for (ci = 0; ci < nc; ci++) {
538 input_ptr = input_buf[row] + ci;
539 output_ptr = output_buf[row];
540 colorindex_ci = cquantize->colorindex[ci];
541 dither = cquantize->odither[ci][row_index];
542 col_index = 0;
543
544 for (col = width; col > 0; col--) {
545 /* Form pixel value + dither, range-limit to 0..MAXJSAMPLE,
546 * select output value, accumulate into output code for this pixel.
547 * Range-limiting need not be done explicitly, as we have extended
548 * the colorindex table to produce the right answers for out-of-range
549 * inputs. The maximum dither is +- MAXJSAMPLE; this sets the
550 * required amount of padding.
551 */
552 *output_ptr += colorindex_ci[GETJSAMPLE(*input_ptr)+dither[col_index]];
553 input_ptr += nc;
554 output_ptr++;
555 col_index = (col_index + 1) & ODITHER_MASK;
556 }
557 }
558 /* Advance row index for next row */
559 row_index = (row_index + 1) & ODITHER_MASK;
560 cquantize->row_index = row_index;
561 }
562}
563
564
565METHODDEF(void)
566quantize3_ord_dither (j_decompress_ptr cinfo, JSAMPARRAY input_buf,
567 JSAMPARRAY output_buf, int num_rows)
568/* Fast path for out_color_components==3, with ordered dithering */
569{
570 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
571 register int pixcode;
572 register JSAMPROW input_ptr;
573 register JSAMPROW output_ptr;
574 JSAMPROW colorindex0 = cquantize->colorindex[0];
575 JSAMPROW colorindex1 = cquantize->colorindex[1];
576 JSAMPROW colorindex2 = cquantize->colorindex[2];
577 int * dither0; /* points to active row of dither matrix */
578 int * dither1;
579 int * dither2;
580 int row_index, col_index; /* current indexes into dither matrix */
581 int row;
582 JDIMENSION col;
583 JDIMENSION width = cinfo->output_width;
584
585 for (row = 0; row < num_rows; row++) {
586 row_index = cquantize->row_index;
587 input_ptr = input_buf[row];
588 output_ptr = output_buf[row];
589 dither0 = cquantize->odither[0][row_index];
590 dither1 = cquantize->odither[1][row_index];
591 dither2 = cquantize->odither[2][row_index];
592 col_index = 0;
593
594 for (col = width; col > 0; col--) {
595 pixcode = GETJSAMPLE(colorindex0[GETJSAMPLE(*input_ptr++) +
596 dither0[col_index]]);
597 pixcode += GETJSAMPLE(colorindex1[GETJSAMPLE(*input_ptr++) +
598 dither1[col_index]]);
599 pixcode += GETJSAMPLE(colorindex2[GETJSAMPLE(*input_ptr++) +
600 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
610METHODDEF(void)
611quantize_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 FMEMZERO((void FAR *) output_buf[row],
640 (size_t) (width * SIZEOF(JSAMPLE)));
641 for (ci = 0; ci < nc; ci++) {
642 input_ptr = input_buf[row] + ci;
643 output_ptr = output_buf[row];
644 if (cquantize->on_odd_row) {
645 /* work right to left in this row */
646 input_ptr += (width-1) * nc; /* so point to rightmost pixel */
647 output_ptr += width-1;
648 dir = -1;
649 dirnc = -nc;
650 errorptr = cquantize->fserrors[ci] + (width+1); /* => entry after last column */
651 } else {
652 /* work left to right in this row */
653 dir = 1;
654 dirnc = nc;
655 errorptr = cquantize->fserrors[ci]; /* => entry before first column */
656 }
657 colorindex_ci = cquantize->colorindex[ci];
658 colormap_ci = cquantize->sv_colormap[ci];
659 /* Preset error values: no error propagated to first pixel from left */
660 cur = 0;
661 /* and no error propagated to row below yet */
662 belowerr = bpreverr = 0;
663
664 for (col = width; col > 0; col--) {
665 /* cur holds the error propagated from the previous pixel on the
666 * current line. Add the error propagated from the previous line
667 * to form the complete error correction term for this pixel, and
668 * round the error term (which is expressed * 16) to an integer.
669 * RIGHT_SHIFT rounds towards minus infinity, so adding 8 is correct
670 * for either sign of the error value.
671 * Note: errorptr points to *previous* column's array entry.
672 */
673 cur = RIGHT_SHIFT(cur + errorptr[dir] + 8, 4);
674 /* Form pixel value + error, and range-limit to 0..MAXJSAMPLE.
675 * The maximum error is +- MAXJSAMPLE; this sets the required size
676 * of the range_limit array.
677 */
678 cur += GETJSAMPLE(*input_ptr);
679 cur = GETJSAMPLE(range_limit[cur]);
680 /* Select output value, accumulate into output code for this pixel */
681 pixcode = GETJSAMPLE(colorindex_ci[cur]);
682 *output_ptr += (JSAMPLE) pixcode;
683 /* Compute actual representation error at this pixel */
684 /* Note: we can do this even though we don't have the final */
685 /* pixel code, because the colormap is orthogonal. */
686 cur -= GETJSAMPLE(colormap_ci[pixcode]);
687 /* Compute error fractions to be propagated to adjacent pixels.
688 * Add these into the running sums, and simultaneously shift the
689 * next-line error sums left by 1 column.
690 */
691 bnexterr = cur;
692 delta = cur * 2;
693 cur += delta; /* form error * 3 */
694 errorptr[0] = (FSERROR) (bpreverr + cur);
695 cur += delta; /* form error * 5 */
696 bpreverr = belowerr + cur;
697 belowerr = bnexterr;
698 cur += delta; /* form error * 7 */
699 /* At this point cur contains the 7/16 error value to be propagated
700 * to the next pixel on the current line, and all the errors for the
701 * next line have been shifted over. We are therefore ready to move on.
702 */
703 input_ptr += dirnc; /* advance input ptr to next column */
704 output_ptr += dir; /* advance output ptr to next column */
705 errorptr += dir; /* advance errorptr to current column */
706 }
707 /* Post-loop cleanup: we must unload the final error value into the
708 * final fserrors[] entry. Note we need not unload belowerr because
709 * it is for the dummy column before or after the actual array.
710 */
711 errorptr[0] = (FSERROR) bpreverr; /* unload prev err into array */
712 }
713 cquantize->on_odd_row = (cquantize->on_odd_row ? FALSE : TRUE);
714 }
715}
716
717
718/*
719 * Allocate workspace for Floyd-Steinberg errors.
720 */
721
722LOCAL(void)
723alloc_fs_workspace (j_decompress_ptr cinfo)
724{
725 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
726 size_t arraysize;
727 int i;
728
729 arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
730 for (i = 0; i < cinfo->out_color_components; i++) {
731 cquantize->fserrors[i] = (FSERRPTR)
732 (*cinfo->mem->alloc_large)((j_common_ptr) cinfo, JPOOL_IMAGE, arraysize);
733 }
734}
735
736
737/*
738 * Initialize for one-pass color quantization.
739 */
740
741METHODDEF(void)
742start_pass_1_quant (j_decompress_ptr cinfo, boolean is_pre_scan)
743{
744 my_cquantize_ptr cquantize = (my_cquantize_ptr) cinfo->cquantize;
745 size_t arraysize;
746 int i;
747
748 /* Install my colormap. */
749 cinfo->colormap = cquantize->sv_colormap;
750 cinfo->actual_number_of_colors = cquantize->sv_actual;
751
752 /* Initialize for desired dithering mode. */
753 switch (cinfo->dither_mode) {
754 case JDITHER_NONE:
755 if (cinfo->out_color_components == 3)
756 cquantize->pub.color_quantize = color_quantize3;
757 else
758 cquantize->pub.color_quantize = color_quantize;
759 break;
760 case JDITHER_ORDERED:
761 if (cinfo->out_color_components == 3)
762 cquantize->pub.color_quantize = quantize3_ord_dither;
763 else
764 cquantize->pub.color_quantize = quantize_ord_dither;
765 cquantize->row_index = 0; /* initialize state for ordered dither */
766 /* If user changed to ordered dither from another mode,
767 * we must recreate the color index table with padding.
768 * This will cost extra space, but probably isn't very likely.
769 */
770 if (! cquantize->is_padded)
771 create_colorindex(cinfo);
772 /* Create ordered-dither tables if we didn't already. */
773 if (cquantize->odither[0] == NULL)
774 create_odither_tables(cinfo);
775 break;
776 case JDITHER_FS:
777 cquantize->pub.color_quantize = quantize_fs_dither;
778 cquantize->on_odd_row = FALSE; /* initialize state for F-S dither */
779 /* Allocate Floyd-Steinberg workspace if didn't already. */
780 if (cquantize->fserrors[0] == NULL)
781 alloc_fs_workspace(cinfo);
782 /* Initialize the propagated errors to zero. */
783 arraysize = (size_t) ((cinfo->output_width + 2) * SIZEOF(FSERROR));
784 for (i = 0; i < cinfo->out_color_components; i++)
785 FMEMZERO((void FAR *) cquantize->fserrors[i], arraysize);
786 break;
787 default:
788 ERREXIT(cinfo, JERR_NOT_COMPILED);
789 break;
790 }
791}
792
793
794/*
795 * Finish up at the end of the pass.
796 */
797
798METHODDEF(void)
799finish_pass_1_quant (j_decompress_ptr cinfo)
800{
801 /* no work in 1-pass case */
802}
803
804
805/*
806 * Switch to a new external colormap between output passes.
807 * Shouldn't get to this module!
808 */
809
810METHODDEF(void)
811new_color_map_1_quant (j_decompress_ptr cinfo)
812{
813 ERREXIT(cinfo, JERR_MODE_CHANGE);
814}
815
816
817/*
818 * Module initialization routine for 1-pass color quantization.
819 */
820
821GLOBAL(void)
822jinit_1pass_quantizer (j_decompress_ptr cinfo)
823{
824 my_cquantize_ptr cquantize;
825
826 cquantize = (my_cquantize_ptr)
827 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
828 SIZEOF(my_cquantizer));
829 cinfo->cquantize = (struct jpeg_color_quantizer *) cquantize;
830 cquantize->pub.start_pass = start_pass_1_quant;
831 cquantize->pub.finish_pass = finish_pass_1_quant;
832 cquantize->pub.new_color_map = new_color_map_1_quant;
833 cquantize->fserrors[0] = NULL; /* Flag FS workspace not allocated */
834 cquantize->odither[0] = NULL; /* Also flag odither arrays not allocated */
835
836 /* Make sure my internal arrays won't overflow */
837 if (cinfo->out_color_components > MAX_Q_COMPS)
838 ERREXIT1(cinfo, JERR_QUANT_COMPONENTS, MAX_Q_COMPS);
839 /* Make sure colormap indexes can be represented by JSAMPLEs */
840 if (cinfo->desired_number_of_colors > (MAXJSAMPLE+1))
841 ERREXIT1(cinfo, JERR_QUANT_MANY_COLORS, MAXJSAMPLE+1);
842
843 /* Create the colormap and color index table. */
844 create_colormap(cinfo);
845 create_colorindex(cinfo);
846
847 /* Allocate Floyd-Steinberg workspace now if requested.
848 * We do this now since it is FAR storage and may affect the memory
849 * manager's space calculations. If the user changes to FS dither
850 * mode in a later pass, we will allocate the space then, and will
851 * possibly overrun the max_memory_to_use setting.
852 */
853 if (cinfo->dither_mode == JDITHER_FS)
854 alloc_fs_workspace(cinfo);
855}
856
857#endif /* QUANT_1PASS_SUPPORTED */
858