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, 2022-2023, D. R. Commander.
8 * For conditions of distribution and use, see the accompanying README.ijg
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.
16 #define JPEG_INTERNALS
19 #include "jsamplecomp.h"
21 #if defined(QUANT_1PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16
25 * The main purpose of 1-pass quantization is to provide a fast, if not very
26 * high quality, colormapped output capability. A 2-pass quantizer usually
27 * gives better visual quality; however, for quantized grayscale output this
28 * quantizer is perfectly adequate. Dithering is highly recommended with this
29 * quantizer, though you can turn it off if you really want to.
31 * In 1-pass quantization the colormap must be chosen in advance of seeing the
32 * image. We use a map consisting of all combinations of Ncolors[i] color
33 * values for the i'th component. The Ncolors[] values are chosen so that
34 * their product, the total number of colors, is no more than that requested.
35 * (In most cases, the product will be somewhat less.)
37 * Since the colormap is orthogonal, the representative value for each color
38 * component can be determined without considering the other components;
39 * then these indexes can be combined into a colormap index by a standard
40 * N-dimensional-array-subscript calculation. Most of the arithmetic involved
41 * can be precalculated and stored in the lookup table colorindex[].
42 * colorindex[i][j] maps pixel value j in component i to the nearest
43 * representative value (grid plane) for that component; this index is
44 * multiplied by the array stride for component i, so that the
45 * index of the colormap entry closest to a given pixel value is just
46 * sum( colorindex[component-number][pixel-component-value] )
47 * Aside from being fast, this scheme allows for variable spacing between
48 * representative values with no additional lookup cost.
50 * If gamma correction has been applied in color conversion, it might be wise
51 * to adjust the color grid spacing so that the representative colors are
52 * equidistant in linear space. At this writing, gamma correction is not
53 * implemented by jdcolor, so nothing is done here.
57 /* Declarations for ordered dithering.
59 * We use a standard 16x16 ordered dither array. The basic concept of ordered
60 * dithering is described in many references, for instance Dale Schumacher's
61 * chapter II.2 of Graphics Gems II (James Arvo, ed. Academic Press, 1991).
62 * In place of Schumacher's comparisons against a "threshold" value, we add a
63 * "dither" value to the input pixel and then round the result to the nearest
64 * output value. The dither value is equivalent to (0.5 - threshold) times
65 * the distance between output values. For ordered dithering, we assume that
66 * the output colors are equally spaced; if not, results will probably be
67 * worse, since the dither may be too much or too little at a given point.
69 * The normal calculation would be to form pixel value + dither, range-limit
70 * this to 0.._MAXJSAMPLE, and then index into the colorindex table as usual.
71 * We can skip the separate range-limiting step by extending the colorindex
72 * table in both directions.
75 #define ODITHER_SIZE 16 /* dimension of dither matrix */
76 /* NB: if ODITHER_SIZE is not a power of 2, ODITHER_MASK uses will break */
77 #define ODITHER_CELLS (ODITHER_SIZE * ODITHER_SIZE) /* # cells in matrix */
78 #define ODITHER_MASK (ODITHER_SIZE - 1) /* mask for wrapping around
81 typedef int ODITHER_MATRIX
[ODITHER_SIZE
][ODITHER_SIZE
];
82 typedef int (*ODITHER_MATRIX_PTR
)[ODITHER_SIZE
];
84 static const UINT8 base_dither_matrix
[ODITHER_SIZE
][ODITHER_SIZE
] = {
85 /* Bayer's order-4 dither array. Generated by the code given in
86 * Stephen Hawley's article "Ordered Dithering" in Graphics Gems I.
87 * The values in this array must range from 0 to ODITHER_CELLS-1.
89 { 0,192, 48,240, 12,204, 60,252, 3,195, 51,243, 15,207, 63,255 },
90 { 128, 64,176,112,140, 76,188,124,131, 67,179,115,143, 79,191,127 },
91 { 32,224, 16,208, 44,236, 28,220, 35,227, 19,211, 47,239, 31,223 },
92 { 160, 96,144, 80,172,108,156, 92,163, 99,147, 83,175,111,159, 95 },
93 { 8,200, 56,248, 4,196, 52,244, 11,203, 59,251, 7,199, 55,247 },
94 { 136, 72,184,120,132, 68,180,116,139, 75,187,123,135, 71,183,119 },
95 { 40,232, 24,216, 36,228, 20,212, 43,235, 27,219, 39,231, 23,215 },
96 { 168,104,152, 88,164,100,148, 84,171,107,155, 91,167,103,151, 87 },
97 { 2,194, 50,242, 14,206, 62,254, 1,193, 49,241, 13,205, 61,253 },
98 { 130, 66,178,114,142, 78,190,126,129, 65,177,113,141, 77,189,125 },
99 { 34,226, 18,210, 46,238, 30,222, 33,225, 17,209, 45,237, 29,221 },
100 { 162, 98,146, 82,174,110,158, 94,161, 97,145, 81,173,109,157, 93 },
101 { 10,202, 58,250, 6,198, 54,246, 9,201, 57,249, 5,197, 53,245 },
102 { 138, 74,186,122,134, 70,182,118,137, 73,185,121,133, 69,181,117 },
103 { 42,234, 26,218, 38,230, 22,214, 41,233, 25,217, 37,229, 21,213 },
104 { 170,106,154, 90,166,102,150, 86,169,105,153, 89,165,101,149, 85 }
108 /* Declarations for Floyd-Steinberg dithering.
110 * Errors are accumulated into the array fserrors[], at a resolution of
111 * 1/16th of a pixel count. The error at a given pixel is propagated
112 * to its not-yet-processed neighbors using the standard F-S fractions,
115 * We work left-to-right on even rows, right-to-left on odd rows.
117 * We can get away with a single array (holding one row's worth of errors)
118 * by using it to store the current row's errors at pixel columns not yet
119 * processed, but the next row's errors at columns already processed. We
120 * need only a few extra variables to hold the errors immediately around the
121 * current column. (If we are lucky, those variables are in registers, but
122 * even if not, they're probably cheaper to access than array elements are.)
124 * The fserrors[] array is indexed [component#][position].
125 * We provide (#columns + 2) entries per component; the extra entry at each
126 * end saves us from special-casing the first and last pixels.
129 #if BITS_IN_JSAMPLE == 8
130 typedef INT16 FSERROR
; /* 16 bits should be enough */
131 typedef int LOCFSERROR
; /* use 'int' for calculation temps */
133 typedef JLONG FSERROR
; /* may need more than 16 bits */
134 typedef JLONG LOCFSERROR
; /* be sure calculation temps are big enough */
137 typedef FSERROR
*FSERRPTR
; /* pointer to error array */
140 /* Private subobject */
142 #define MAX_Q_COMPS 4 /* max components I can handle */
145 struct jpeg_color_quantizer pub
; /* public fields */
147 /* Initially allocated colormap is saved here */
148 _JSAMPARRAY sv_colormap
; /* The color map as a 2-D pixel array */
149 int sv_actual
; /* number of entries in use */
151 _JSAMPARRAY colorindex
; /* Precomputed mapping for speed */
152 /* colorindex[i][j] = index of color closest to pixel value j in component i,
153 * premultiplied as described above. Since colormap indexes must fit into
154 * _JSAMPLEs, the entries of this array will too.
156 boolean is_padded
; /* is the colorindex padded for odither? */
158 int Ncolors
[MAX_Q_COMPS
]; /* # of values allocated to each component */
160 /* Variables for ordered dithering */
161 int row_index
; /* cur row's vertical index in dither matrix */
162 ODITHER_MATRIX_PTR odither
[MAX_Q_COMPS
]; /* one dither array per component */
164 /* Variables for Floyd-Steinberg dithering */
165 FSERRPTR fserrors
[MAX_Q_COMPS
]; /* accumulated errors */
166 boolean on_odd_row
; /* flag to remember which row we are on */
169 typedef my_cquantizer
*my_cquantize_ptr
;
173 * Policy-making subroutines for create_colormap and create_colorindex.
174 * These routines determine the colormap to be used. The rest of the module
175 * only assumes that the colormap is orthogonal.
177 * * select_ncolors decides how to divvy up the available colors
178 * among the components.
179 * * output_value defines the set of representative values for a component.
180 * * largest_input_value defines the mapping from input values to
181 * representative values for a component.
182 * Note that the latter two routines may impose different policies for
183 * different components, though this is not currently done.
188 select_ncolors(j_decompress_ptr cinfo
, int Ncolors
[])
189 /* Determine allocation of desired colors to components, */
190 /* and fill in Ncolors[] array to indicate choice. */
191 /* Return value is total number of colors (product of Ncolors[] values). */
193 int nc
= cinfo
->out_color_components
; /* number of color components */
194 int max_colors
= cinfo
->desired_number_of_colors
;
195 int total_colors
, iroot
, i
, j
;
198 int RGB_order
[3] = { RGB_GREEN
, RGB_RED
, RGB_BLUE
};
199 RGB_order
[0] = rgb_green
[cinfo
->out_color_space
];
200 RGB_order
[1] = rgb_red
[cinfo
->out_color_space
];
201 RGB_order
[2] = rgb_blue
[cinfo
->out_color_space
];
203 /* We can allocate at least the nc'th root of max_colors per component. */
204 /* Compute floor(nc'th root of max_colors). */
208 temp
= iroot
; /* set temp = iroot ** nc */
209 for (i
= 1; i
< nc
; i
++)
211 } while (temp
<= (long)max_colors
); /* repeat till iroot exceeds root */
212 iroot
--; /* now iroot = floor(root) */
214 /* Must have at least 2 color values per component */
216 ERREXIT1(cinfo
, JERR_QUANT_FEW_COLORS
, (int)temp
);
218 /* Initialize to iroot color values for each component */
220 for (i
= 0; i
< nc
; i
++) {
222 total_colors
*= iroot
;
224 /* We may be able to increment the count for one or more components without
225 * exceeding max_colors, though we know not all can be incremented.
226 * Sometimes, the first component can be incremented more than once!
227 * (Example: for 16 colors, we start at 2*2*2, go to 3*2*2, then 4*2*2.)
228 * In RGB colorspace, try to increment G first, then R, then B.
232 for (i
= 0; i
< nc
; i
++) {
233 j
= (cinfo
->out_color_space
== JCS_RGB
? RGB_order
[i
] : i
);
234 /* calculate new total_colors if Ncolors[j] is incremented */
235 temp
= total_colors
/ Ncolors
[j
];
236 temp
*= Ncolors
[j
] + 1; /* done in long arith to avoid oflo */
237 if (temp
> (long)max_colors
)
238 break; /* won't fit, done with this pass */
239 Ncolors
[j
]++; /* OK, apply the increment */
240 total_colors
= (int)temp
;
250 output_value(j_decompress_ptr cinfo
, int ci
, int j
, int maxj
)
251 /* Return j'th output value, where j will range from 0 to maxj */
252 /* The output values must fall in 0.._MAXJSAMPLE in increasing order */
254 /* We always provide values 0 and _MAXJSAMPLE for each component;
255 * any additional values are equally spaced between these limits.
256 * (Forcing the upper and lower values to the limits ensures that
257 * dithering can't produce a color outside the selected gamut.)
259 return (int)(((JLONG
)j
* _MAXJSAMPLE
+ maxj
/ 2) / maxj
);
264 largest_input_value(j_decompress_ptr cinfo
, int ci
, int j
, int maxj
)
265 /* Return largest input value that should map to j'th output value */
266 /* Must have largest(j=0) >= 0, and largest(j=maxj) >= _MAXJSAMPLE */
268 /* Breakpoints are halfway between values returned by output_value */
269 return (int)(((JLONG
)(2 * j
+ 1) * _MAXJSAMPLE
+ maxj
) / (2 * maxj
));
274 * Create the colormap.
278 create_colormap(j_decompress_ptr cinfo
)
280 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
281 _JSAMPARRAY colormap
; /* Created colormap */
282 int total_colors
; /* Number of distinct output colors */
283 int i
, j
, k
, nci
, blksize
, blkdist
, ptr
, val
;
285 /* Select number of colors for each component */
286 total_colors
= select_ncolors(cinfo
, cquantize
->Ncolors
);
288 /* Report selected color counts */
289 if (cinfo
->out_color_components
== 3)
290 TRACEMS4(cinfo
, 1, JTRC_QUANT_3_NCOLORS
, total_colors
,
291 cquantize
->Ncolors
[0], cquantize
->Ncolors
[1],
292 cquantize
->Ncolors
[2]);
294 TRACEMS1(cinfo
, 1, JTRC_QUANT_NCOLORS
, total_colors
);
296 /* Allocate and fill in the colormap. */
297 /* The colors are ordered in the map in standard row-major order, */
298 /* i.e. rightmost (highest-indexed) color changes most rapidly. */
300 colormap
= (_JSAMPARRAY
)(*cinfo
->mem
->alloc_sarray
)
301 ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
302 (JDIMENSION
)total_colors
, (JDIMENSION
)cinfo
->out_color_components
);
304 /* blksize is number of adjacent repeated entries for a component */
305 /* blkdist is distance between groups of identical entries for a component */
306 blkdist
= total_colors
;
308 for (i
= 0; i
< cinfo
->out_color_components
; i
++) {
309 /* fill in colormap entries for i'th color component */
310 nci
= cquantize
->Ncolors
[i
]; /* # of distinct values for this color */
311 blksize
= blkdist
/ nci
;
312 for (j
= 0; j
< nci
; j
++) {
313 /* Compute j'th output value (out of nci) for component */
314 val
= output_value(cinfo
, i
, j
, nci
- 1);
315 /* Fill in all colormap entries that have this value of this component */
316 for (ptr
= j
* blksize
; ptr
< total_colors
; ptr
+= blkdist
) {
317 /* fill in blksize entries beginning at ptr */
318 for (k
= 0; k
< blksize
; k
++)
319 colormap
[i
][ptr
+ k
] = (_JSAMPLE
)val
;
322 blkdist
= blksize
; /* blksize of this color is blkdist of next */
325 /* Save the colormap in private storage,
326 * where it will survive color quantization mode changes.
328 cquantize
->sv_colormap
= colormap
;
329 cquantize
->sv_actual
= total_colors
;
334 * Create the color index table.
338 create_colorindex(j_decompress_ptr cinfo
)
340 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
342 int i
, j
, k
, nci
, blksize
, val
, pad
;
344 /* For ordered dither, we pad the color index tables by _MAXJSAMPLE in
345 * each direction (input index values can be -_MAXJSAMPLE .. 2*_MAXJSAMPLE).
346 * This is not necessary in the other dithering modes. However, we
347 * flag whether it was done in case user changes dithering mode.
349 if (cinfo
->dither_mode
== JDITHER_ORDERED
) {
350 pad
= _MAXJSAMPLE
* 2;
351 cquantize
->is_padded
= TRUE
;
354 cquantize
->is_padded
= FALSE
;
357 cquantize
->colorindex
= (_JSAMPARRAY
)(*cinfo
->mem
->alloc_sarray
)
358 ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
359 (JDIMENSION
)(_MAXJSAMPLE
+ 1 + pad
),
360 (JDIMENSION
)cinfo
->out_color_components
);
362 /* blksize is number of adjacent repeated entries for a component */
363 blksize
= cquantize
->sv_actual
;
365 for (i
= 0; i
< cinfo
->out_color_components
; i
++) {
366 /* fill in colorindex entries for i'th color component */
367 nci
= cquantize
->Ncolors
[i
]; /* # of distinct values for this color */
368 blksize
= blksize
/ nci
;
370 /* adjust colorindex pointers to provide padding at negative indexes. */
372 cquantize
->colorindex
[i
] += _MAXJSAMPLE
;
374 /* in loop, val = index of current output value, */
375 /* and k = largest j that maps to current val */
376 indexptr
= cquantize
->colorindex
[i
];
378 k
= largest_input_value(cinfo
, i
, 0, nci
- 1);
379 for (j
= 0; j
<= _MAXJSAMPLE
; j
++) {
380 while (j
> k
) /* advance val if past boundary */
381 k
= largest_input_value(cinfo
, i
, ++val
, nci
- 1);
382 /* premultiply so that no multiplication needed in main processing */
383 indexptr
[j
] = (_JSAMPLE
)(val
* blksize
);
385 /* Pad at both ends if necessary */
387 for (j
= 1; j
<= _MAXJSAMPLE
; j
++) {
388 indexptr
[-j
] = indexptr
[0];
389 indexptr
[_MAXJSAMPLE
+ j
] = indexptr
[_MAXJSAMPLE
];
396 * Create an ordered-dither array for a component having ncolors
397 * distinct output values.
400 LOCAL(ODITHER_MATRIX_PTR
)
401 make_odither_array(j_decompress_ptr cinfo
, int ncolors
)
403 ODITHER_MATRIX_PTR odither
;
407 odither
= (ODITHER_MATRIX_PTR
)
408 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
409 sizeof(ODITHER_MATRIX
));
410 /* The inter-value distance for this color is _MAXJSAMPLE/(ncolors-1).
411 * Hence the dither value for the matrix cell with fill order f
412 * (f=0..N-1) should be (N-1-2*f)/(2*N) * _MAXJSAMPLE/(ncolors-1).
413 * On 16-bit-int machine, be careful to avoid overflow.
415 den
= 2 * ODITHER_CELLS
* ((JLONG
)(ncolors
- 1));
416 for (j
= 0; j
< ODITHER_SIZE
; j
++) {
417 for (k
= 0; k
< ODITHER_SIZE
; k
++) {
418 num
= ((JLONG
)(ODITHER_CELLS
- 1 -
419 2 * ((int)base_dither_matrix
[j
][k
]))) * _MAXJSAMPLE
;
420 /* Ensure round towards zero despite C's lack of consistency
421 * about rounding negative values in integer division...
423 odither
[j
][k
] = (int)(num
< 0 ? -((-num
) / den
) : num
/ den
);
431 * Create the ordered-dither tables.
432 * Components having the same number of representative colors may
433 * share a dither table.
437 create_odither_tables(j_decompress_ptr cinfo
)
439 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
440 ODITHER_MATRIX_PTR odither
;
443 for (i
= 0; i
< cinfo
->out_color_components
; i
++) {
444 nci
= cquantize
->Ncolors
[i
]; /* # of distinct values for this color */
445 odither
= NULL
; /* search for matching prior component */
446 for (j
= 0; j
< i
; j
++) {
447 if (nci
== cquantize
->Ncolors
[j
]) {
448 odither
= cquantize
->odither
[j
];
452 if (odither
== NULL
) /* need a new table? */
453 odither
= make_odither_array(cinfo
, nci
);
454 cquantize
->odither
[i
] = odither
;
460 * Map some rows of pixels to the output colormapped representation.
464 color_quantize(j_decompress_ptr cinfo
, _JSAMPARRAY input_buf
,
465 _JSAMPARRAY output_buf
, int num_rows
)
466 /* General case, no dithering */
468 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
469 _JSAMPARRAY colorindex
= cquantize
->colorindex
;
470 register int pixcode
, ci
;
471 register _JSAMPROW ptrin
, ptrout
;
474 JDIMENSION width
= cinfo
->output_width
;
475 register int nc
= cinfo
->out_color_components
;
477 for (row
= 0; row
< num_rows
; row
++) {
478 ptrin
= input_buf
[row
];
479 ptrout
= output_buf
[row
];
480 for (col
= width
; col
> 0; col
--) {
482 for (ci
= 0; ci
< nc
; ci
++) {
483 pixcode
+= colorindex
[ci
][*ptrin
++];
485 *ptrout
++ = (_JSAMPLE
)pixcode
;
492 color_quantize3(j_decompress_ptr cinfo
, _JSAMPARRAY input_buf
,
493 _JSAMPARRAY output_buf
, int num_rows
)
494 /* Fast path for out_color_components==3, no dithering */
496 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
497 register int pixcode
;
498 register _JSAMPROW ptrin
, ptrout
;
499 _JSAMPROW colorindex0
= cquantize
->colorindex
[0];
500 _JSAMPROW colorindex1
= cquantize
->colorindex
[1];
501 _JSAMPROW colorindex2
= cquantize
->colorindex
[2];
504 JDIMENSION width
= cinfo
->output_width
;
506 for (row
= 0; row
< num_rows
; row
++) {
507 ptrin
= input_buf
[row
];
508 ptrout
= output_buf
[row
];
509 for (col
= width
; col
> 0; col
--) {
510 pixcode
= colorindex0
[*ptrin
++];
511 pixcode
+= colorindex1
[*ptrin
++];
512 pixcode
+= colorindex2
[*ptrin
++];
513 *ptrout
++ = (_JSAMPLE
)pixcode
;
520 quantize_ord_dither(j_decompress_ptr cinfo
, _JSAMPARRAY input_buf
,
521 _JSAMPARRAY output_buf
, int num_rows
)
522 /* General case, with ordered dithering */
524 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
525 register _JSAMPROW input_ptr
;
526 register _JSAMPROW output_ptr
;
527 _JSAMPROW colorindex_ci
;
528 int *dither
; /* points to active row of dither matrix */
529 int row_index
, col_index
; /* current indexes into dither matrix */
530 int nc
= cinfo
->out_color_components
;
534 JDIMENSION width
= cinfo
->output_width
;
536 for (row
= 0; row
< num_rows
; row
++) {
537 /* Initialize output values to 0 so can process components separately */
538 jzero_far((void *)output_buf
[row
], (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.
556 colorindex_ci
[*input_ptr
+ dither
[col_index
]];
559 col_index
= (col_index
+ 1) & ODITHER_MASK
;
562 /* Advance row index for next row */
563 row_index
= (row_index
+ 1) & ODITHER_MASK
;
564 cquantize
->row_index
= row_index
;
570 quantize3_ord_dither(j_decompress_ptr cinfo
, _JSAMPARRAY input_buf
,
571 _JSAMPARRAY output_buf
, int num_rows
)
572 /* Fast path for out_color_components==3, with ordered dithering */
574 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
575 register int pixcode
;
576 register _JSAMPROW input_ptr
;
577 register _JSAMPROW output_ptr
;
578 _JSAMPROW colorindex0
= cquantize
->colorindex
[0];
579 _JSAMPROW colorindex1
= cquantize
->colorindex
[1];
580 _JSAMPROW colorindex2
= cquantize
->colorindex
[2];
581 int *dither0
; /* points to active row of dither matrix */
584 int row_index
, col_index
; /* current indexes into dither matrix */
587 JDIMENSION width
= cinfo
->output_width
;
589 for (row
= 0; row
< num_rows
; row
++) {
590 row_index
= cquantize
->row_index
;
591 input_ptr
= input_buf
[row
];
592 output_ptr
= output_buf
[row
];
593 dither0
= cquantize
->odither
[0][row_index
];
594 dither1
= cquantize
->odither
[1][row_index
];
595 dither2
= cquantize
->odither
[2][row_index
];
598 for (col
= width
; col
> 0; col
--) {
599 pixcode
= colorindex0
[(*input_ptr
++) + dither0
[col_index
]];
600 pixcode
+= colorindex1
[(*input_ptr
++) + dither1
[col_index
]];
601 pixcode
+= colorindex2
[(*input_ptr
++) + dither2
[col_index
]];
602 *output_ptr
++ = (_JSAMPLE
)pixcode
;
603 col_index
= (col_index
+ 1) & ODITHER_MASK
;
605 row_index
= (row_index
+ 1) & ODITHER_MASK
;
606 cquantize
->row_index
= row_index
;
612 quantize_fs_dither(j_decompress_ptr cinfo
, _JSAMPARRAY input_buf
,
613 _JSAMPARRAY output_buf
, int num_rows
)
614 /* General case, with Floyd-Steinberg dithering */
616 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
617 register LOCFSERROR cur
; /* current error or pixel value */
618 LOCFSERROR belowerr
; /* error for pixel below cur */
619 LOCFSERROR bpreverr
; /* error for below/prev col */
620 LOCFSERROR bnexterr
; /* error for below/next col */
622 register FSERRPTR errorptr
; /* => fserrors[] at column before current */
623 register _JSAMPROW input_ptr
;
624 register _JSAMPROW output_ptr
;
625 _JSAMPROW colorindex_ci
;
626 _JSAMPROW colormap_ci
;
628 int nc
= cinfo
->out_color_components
;
629 int dir
; /* 1 for left-to-right, -1 for right-to-left */
630 int dirnc
; /* dir * nc */
634 JDIMENSION width
= cinfo
->output_width
;
635 _JSAMPLE
*range_limit
= (_JSAMPLE
*)cinfo
->sample_range_limit
;
638 for (row
= 0; row
< num_rows
; row
++) {
639 /* Initialize output values to 0 so can process components separately */
640 jzero_far((void *)output_buf
[row
], (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;
650 errorptr
= cquantize
->fserrors
[ci
] + (width
+ 1); /* => entry after last column */
652 /* work left to right in this row */
655 errorptr
= cquantize
->fserrors
[ci
]; /* => entry before first column */
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 */
661 /* and no error propagated to row below yet */
662 belowerr
= bpreverr
= 0;
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.
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.
679 cur
= range_limit
[cur
];
680 /* Select output value, accumulate into output code for this pixel */
681 pixcode
= 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
-= 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.
693 cur
+= delta
; /* form error * 3 */
694 errorptr
[0] = (FSERROR
)(bpreverr
+ cur
);
695 cur
+= delta
; /* form error * 5 */
696 bpreverr
= belowerr
+ cur
;
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.
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 */
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.
711 errorptr
[0] = (FSERROR
)bpreverr
; /* unload prev err into array */
713 cquantize
->on_odd_row
= (cquantize
->on_odd_row
? FALSE
: TRUE
);
719 * Allocate workspace for Floyd-Steinberg errors.
723 alloc_fs_workspace(j_decompress_ptr cinfo
)
725 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
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
);
738 * Initialize for one-pass color quantization.
742 start_pass_1_quant(j_decompress_ptr cinfo
, boolean is_pre_scan
)
744 my_cquantize_ptr cquantize
= (my_cquantize_ptr
)cinfo
->cquantize
;
748 /* Install my colormap. */
749 cinfo
->colormap
= (JSAMPARRAY
)cquantize
->sv_colormap
;
750 cinfo
->actual_number_of_colors
= cquantize
->sv_actual
;
752 /* Initialize for desired dithering mode. */
753 switch (cinfo
->dither_mode
) {
755 if (cinfo
->out_color_components
== 3)
756 cquantize
->pub
._color_quantize
= color_quantize3
;
758 cquantize
->pub
._color_quantize
= color_quantize
;
760 case JDITHER_ORDERED
:
761 if (cinfo
->out_color_components
== 3)
762 cquantize
->pub
._color_quantize
= quantize3_ord_dither
;
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.
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
);
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 jzero_far((void *)cquantize
->fserrors
[i
], arraysize
);
788 ERREXIT(cinfo
, JERR_NOT_COMPILED
);
795 * Finish up at the end of the pass.
799 finish_pass_1_quant(j_decompress_ptr cinfo
)
801 /* no work in 1-pass case */
806 * Switch to a new external colormap between output passes.
807 * Shouldn't get to this module!
811 new_color_map_1_quant(j_decompress_ptr cinfo
)
813 ERREXIT(cinfo
, JERR_MODE_CHANGE
);
818 * Module initialization routine for 1-pass color quantization.
822 _jinit_1pass_quantizer(j_decompress_ptr cinfo
)
824 my_cquantize_ptr cquantize
;
826 if (cinfo
->data_precision
!= BITS_IN_JSAMPLE
)
827 ERREXIT1(cinfo
, JERR_BAD_PRECISION
, cinfo
->data_precision
);
829 /* Color quantization is not supported with lossless JPEG images */
830 if (cinfo
->master
->lossless
)
831 ERREXIT(cinfo
, JERR_NOTIMPL
);
833 cquantize
= (my_cquantize_ptr
)
834 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
)cinfo
, JPOOL_IMAGE
,
835 sizeof(my_cquantizer
));
836 cinfo
->cquantize
= (struct jpeg_color_quantizer
*)cquantize
;
837 cquantize
->pub
.start_pass
= start_pass_1_quant
;
838 cquantize
->pub
.finish_pass
= finish_pass_1_quant
;
839 cquantize
->pub
.new_color_map
= new_color_map_1_quant
;
840 cquantize
->fserrors
[0] = NULL
; /* Flag FS workspace not allocated */
841 cquantize
->odither
[0] = NULL
; /* Also flag odither arrays not allocated */
843 /* Make sure my internal arrays won't overflow */
844 if (cinfo
->out_color_components
> MAX_Q_COMPS
)
845 ERREXIT1(cinfo
, JERR_QUANT_COMPONENTS
, MAX_Q_COMPS
);
846 /* Make sure colormap indexes can be represented by _JSAMPLEs */
847 if (cinfo
->desired_number_of_colors
> (_MAXJSAMPLE
+ 1))
848 ERREXIT1(cinfo
, JERR_QUANT_MANY_COLORS
, _MAXJSAMPLE
+ 1);
850 /* Create the colormap and color index table. */
851 create_colormap(cinfo
);
852 create_colorindex(cinfo
);
854 /* Allocate Floyd-Steinberg workspace now if requested.
855 * We do this now since it may affect the memory manager's space
856 * calculations. If the user changes to FS dither mode in a later pass, we
857 * will allocate the space then, and will possibly overrun the
858 * max_memory_to_use setting.
860 if (cinfo
->dither_mode
== JDITHER_FS
)
861 alloc_fs_workspace(cinfo
);
864 #endif /* defined(QUANT_1PASS_SUPPORTED) && BITS_IN_JSAMPLE != 16 */