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 downsampling routines.
10
* Downsampling input data is counted in "row groups". A row group
11
* is defined to be max_v_samp_factor pixel rows of each component,
12
* from which the downsampler produces v_samp_factor sample rows.
13
* A single row group is processed in each call to the downsampler module.
15
* The downsampler is responsible for edge-expansion of its output data
16
* to fill an integral number of DCT blocks horizontally. The source buffer
17
* may be modified if it is helpful for this purpose (the source buffer is
18
* allocated wide enough to correspond to the desired output width).
19
* The caller (the prep controller) is responsible for vertical padding.
21
* The downsampler may request "context rows" by setting need_context_rows
22
* during startup. In this case, the input arrays will contain at least
23
* one row group's worth of pixels above and below the passed-in data;
24
* the caller will create dummy rows at image top and bottom by replicating
25
* the first or last real pixel row.
27
* An excellent reference for image resampling is
28
* Digital Image Warping, George Wolberg, 1990.
29
* Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
31
* The downsampling algorithm used here is a simple average of the source
32
* pixels covered by the output pixel. The hi-falutin sampling literature
33
* refers to this as a "box filter". In general the characteristics of a box
34
* filter are not very good, but for the specific cases we normally use (1:1
35
* and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
36
* nearly so bad. If you intend to use other sampling ratios, you'd be well
37
* advised to improve this code.
39
* A simple input-smoothing capability is provided. This is mainly intended
40
* for cleaning up color-dithered GIF input files (if you find it inadequate,
41
* we suggest using an external filtering program such as pnmconvol). When
42
* enabled, each input pixel P is replaced by a weighted sum of itself and its
43
* eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF,
44
* where SF = (smoothing_factor / 1024).
45
* Currently, smoothing is only supported for 2h2v sampling factors.
48
#define JPEG_INTERNALS
53
/* Pointer to routine to downsample a single component */
54
typedef JMETHOD(void, downsample1_ptr,
55
(j_compress_ptr cinfo, jpeg_component_info * compptr,
56
JSAMPARRAY input_data, JSAMPARRAY output_data));
58
/* Private subobject */
61
struct jpeg_downsampler pub; /* public fields */
63
/* Downsampling method pointers, one per component */
64
downsample1_ptr methods[MAX_COMPONENTS];
66
/* Height of an output row group for each component. */
67
int rowgroup_height[MAX_COMPONENTS];
69
/* These arrays save pixel expansion factors so that int_downsample need not
70
* recompute them each time. They are unused for other downsampling methods.
72
UINT8 h_expand[MAX_COMPONENTS];
73
UINT8 v_expand[MAX_COMPONENTS];
76
typedef my_downsampler * my_downsample_ptr;
80
* Initialize for a downsampling pass.
84
start_pass_downsample (j_compress_ptr cinfo)
91
* Expand a component horizontally from width input_cols to width output_cols,
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* by duplicating the rightmost samples.
96
expand_right_edge (JSAMPARRAY image_data, int num_rows,
97
JDIMENSION input_cols, JDIMENSION output_cols)
99
register JSAMPROW ptr;
100
register JSAMPLE pixval;
103
int numcols = (int) (output_cols - input_cols);
106
for (row = 0; row < num_rows; row++) {
107
ptr = image_data[row] + input_cols;
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pixval = ptr[-1]; /* don't need GETJSAMPLE() here */
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for (count = numcols; count > 0; count--)
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* Do downsampling for a whole row group (all components).
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* In this version we simply downsample each component independently.
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sep_downsample (j_compress_ptr cinfo,
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JSAMPIMAGE input_buf, JDIMENSION in_row_index,
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JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
127
my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
129
jpeg_component_info * compptr;
130
JSAMPARRAY in_ptr, out_ptr;
132
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
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in_ptr = input_buf[ci] + in_row_index;
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out_ptr = output_buf[ci] +
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(out_row_group_index * downsample->rowgroup_height[ci]);
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(*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
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* Downsample pixel values of a single component.
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* One row group is processed per call.
145
* This version handles arbitrary integral sampling ratios, without smoothing.
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* Note that this version is not actually used for customary sampling ratios.
150
int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
151
JSAMPARRAY input_data, JSAMPARRAY output_data)
153
my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
154
int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
155
JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */
156
JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
157
JSAMPROW inptr, outptr;
160
h_expand = downsample->h_expand[compptr->component_index];
161
v_expand = downsample->v_expand[compptr->component_index];
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numpix = h_expand * v_expand;
165
/* Expand input data enough to let all the output samples be generated
166
* by the standard loop. Special-casing padded output would be more
169
expand_right_edge(input_data, cinfo->max_v_samp_factor,
170
cinfo->image_width, output_cols * h_expand);
173
while (inrow < cinfo->max_v_samp_factor) {
174
outptr = output_data[outrow];
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for (outcol = 0, outcol_h = 0; outcol < output_cols;
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outcol++, outcol_h += h_expand) {
178
for (v = 0; v < v_expand; v++) {
179
inptr = input_data[inrow+v] + outcol_h;
180
for (h = 0; h < h_expand; h++) {
181
outvalue += (INT32) GETJSAMPLE(*inptr++);
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*outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
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* Downsample pixel values of a single component.
194
* This version handles the special case of a full-size component,
199
fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
200
JSAMPARRAY input_data, JSAMPARRAY output_data)
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jcopy_sample_rows(input_data, 0, output_data, 0,
204
cinfo->max_v_samp_factor, cinfo->image_width);
206
expand_right_edge(output_data, cinfo->max_v_samp_factor, cinfo->image_width,
207
compptr->width_in_blocks * compptr->DCT_h_scaled_size);
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* Downsample pixel values of a single component.
213
* This version handles the common case of 2:1 horizontal and 1:1 vertical,
216
* A note about the "bias" calculations: when rounding fractional values to
217
* integer, we do not want to always round 0.5 up to the next integer.
218
* If we did that, we'd introduce a noticeable bias towards larger values.
219
* Instead, this code is arranged so that 0.5 will be rounded up or down at
220
* alternate pixel locations (a simple ordered dither pattern).
224
h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
225
JSAMPARRAY input_data, JSAMPARRAY output_data)
229
JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
230
register JSAMPROW inptr, outptr;
233
/* Expand input data enough to let all the output samples be generated
234
* by the standard loop. Special-casing padded output would be more
237
expand_right_edge(input_data, cinfo->max_v_samp_factor,
238
cinfo->image_width, output_cols * 2);
240
for (inrow = 0; inrow < cinfo->max_v_samp_factor; inrow++) {
241
outptr = output_data[inrow];
242
inptr = input_data[inrow];
243
bias = 0; /* bias = 0,1,0,1,... for successive samples */
244
for (outcol = 0; outcol < output_cols; outcol++) {
245
*outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
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bias ^= 1; /* 0=>1, 1=>0 */
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* Downsample pixel values of a single component.
256
* This version handles the standard case of 2:1 horizontal and 2:1 vertical,
261
h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
262
JSAMPARRAY input_data, JSAMPARRAY output_data)
266
JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
267
register JSAMPROW inptr0, inptr1, outptr;
270
/* Expand input data enough to let all the output samples be generated
271
* by the standard loop. Special-casing padded output would be more
274
expand_right_edge(input_data, cinfo->max_v_samp_factor,
275
cinfo->image_width, output_cols * 2);
278
while (inrow < cinfo->max_v_samp_factor) {
279
outptr = output_data[outrow];
280
inptr0 = input_data[inrow];
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inptr1 = input_data[inrow+1];
282
bias = 1; /* bias = 1,2,1,2,... for successive samples */
283
for (outcol = 0; outcol < output_cols; outcol++) {
284
*outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
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GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
287
bias ^= 3; /* 1=>2, 2=>1 */
288
inptr0 += 2; inptr1 += 2;
296
#ifdef INPUT_SMOOTHING_SUPPORTED
299
* Downsample pixel values of a single component.
300
* This version handles the standard case of 2:1 horizontal and 2:1 vertical,
301
* with smoothing. One row of context is required.
305
h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
306
JSAMPARRAY input_data, JSAMPARRAY output_data)
310
JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
311
register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
312
INT32 membersum, neighsum, memberscale, neighscale;
314
/* Expand input data enough to let all the output samples be generated
315
* by the standard loop. Special-casing padded output would be more
318
expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
319
cinfo->image_width, output_cols * 2);
321
/* We don't bother to form the individual "smoothed" input pixel values;
322
* we can directly compute the output which is the average of the four
323
* smoothed values. Each of the four member pixels contributes a fraction
324
* (1-8*SF) to its own smoothed image and a fraction SF to each of the three
325
* other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
326
* output. The four corner-adjacent neighbor pixels contribute a fraction
327
* SF to just one smoothed pixel, or SF/4 to the final output; while the
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* eight edge-adjacent neighbors contribute SF to each of two smoothed
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* pixels, or SF/2 overall. In order to use integer arithmetic, these
330
* factors are scaled by 2^16 = 65536.
331
* Also recall that SF = smoothing_factor / 1024.
334
memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
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neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
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while (inrow < cinfo->max_v_samp_factor) {
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outptr = output_data[outrow];
340
inptr0 = input_data[inrow];
341
inptr1 = input_data[inrow+1];
342
above_ptr = input_data[inrow-1];
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below_ptr = input_data[inrow+2];
345
/* Special case for first column: pretend column -1 is same as column 0 */
346
membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
347
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
348
neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
349
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
350
GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
351
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
352
neighsum += neighsum;
353
neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
354
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]);
355
membersum = membersum * memberscale + neighsum * neighscale;
356
*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
357
inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
359
for (colctr = output_cols - 2; colctr > 0; colctr--) {
360
/* sum of pixels directly mapped to this output element */
361
membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
362
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
363
/* sum of edge-neighbor pixels */
364
neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
365
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
366
GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
367
GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
368
/* The edge-neighbors count twice as much as corner-neighbors */
369
neighsum += neighsum;
370
/* Add in the corner-neighbors */
371
neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
372
GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
373
/* form final output scaled up by 2^16 */
374
membersum = membersum * memberscale + neighsum * neighscale;
375
/* round, descale and output it */
376
*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
377
inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
380
/* Special case for last column */
381
membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
382
GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
383
neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
384
GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
385
GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
386
GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
387
neighsum += neighsum;
388
neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
389
GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
390
membersum = membersum * memberscale + neighsum * neighscale;
391
*outptr = (JSAMPLE) ((membersum + 32768) >> 16);
400
* Downsample pixel values of a single component.
401
* This version handles the special case of a full-size component,
402
* with smoothing. One row of context is required.
406
fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
407
JSAMPARRAY input_data, JSAMPARRAY output_data)
411
JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
412
register JSAMPROW inptr, above_ptr, below_ptr, outptr;
413
INT32 membersum, neighsum, memberscale, neighscale;
414
int colsum, lastcolsum, nextcolsum;
416
/* Expand input data enough to let all the output samples be generated
417
* by the standard loop. Special-casing padded output would be more
420
expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
421
cinfo->image_width, output_cols);
423
/* Each of the eight neighbor pixels contributes a fraction SF to the
424
* smoothed pixel, while the main pixel contributes (1-8*SF). In order
425
* to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
426
* Also recall that SF = smoothing_factor / 1024.
429
memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
430
neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
432
for (inrow = 0; inrow < cinfo->max_v_samp_factor; inrow++) {
433
outptr = output_data[inrow];
434
inptr = input_data[inrow];
435
above_ptr = input_data[inrow-1];
436
below_ptr = input_data[inrow+1];
438
/* Special case for first column */
439
colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
441
membersum = GETJSAMPLE(*inptr++);
442
nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
444
neighsum = colsum + (colsum - membersum) + nextcolsum;
445
membersum = membersum * memberscale + neighsum * neighscale;
446
*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
447
lastcolsum = colsum; colsum = nextcolsum;
449
for (colctr = output_cols - 2; colctr > 0; colctr--) {
450
membersum = GETJSAMPLE(*inptr++);
451
above_ptr++; below_ptr++;
452
nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
454
neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
455
membersum = membersum * memberscale + neighsum * neighscale;
456
*outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
457
lastcolsum = colsum; colsum = nextcolsum;
460
/* Special case for last column */
461
membersum = GETJSAMPLE(*inptr);
462
neighsum = lastcolsum + (colsum - membersum) + colsum;
463
membersum = membersum * memberscale + neighsum * neighscale;
464
*outptr = (JSAMPLE) ((membersum + 32768) >> 16);
469
#endif /* INPUT_SMOOTHING_SUPPORTED */
473
* Module initialization routine for downsampling.
474
* Note that we must select a routine for each component.
478
jinit_downsampler (j_compress_ptr cinfo)
480
my_downsample_ptr downsample;
482
jpeg_component_info * compptr;
483
boolean smoothok = TRUE;
484
int h_in_group, v_in_group, h_out_group, v_out_group;
486
downsample = (my_downsample_ptr)
487
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
488
SIZEOF(my_downsampler));
489
cinfo->downsample = (struct jpeg_downsampler *) downsample;
490
downsample->pub.start_pass = start_pass_downsample;
491
downsample->pub.downsample = sep_downsample;
492
downsample->pub.need_context_rows = FALSE;
494
if (cinfo->CCIR601_sampling)
495
ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
497
/* Verify we can handle the sampling factors, and set up method pointers */
498
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
500
/* Compute size of an "output group" for DCT scaling. This many samples
501
* are to be converted from max_h_samp_factor * max_v_samp_factor pixels.
503
h_out_group = (compptr->h_samp_factor * compptr->DCT_h_scaled_size) /
504
cinfo->min_DCT_h_scaled_size;
505
v_out_group = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) /
506
cinfo->min_DCT_v_scaled_size;
507
h_in_group = cinfo->max_h_samp_factor;
508
v_in_group = cinfo->max_v_samp_factor;
509
downsample->rowgroup_height[ci] = v_out_group; /* save for use later */
510
if (h_in_group == h_out_group && v_in_group == v_out_group) {
511
#ifdef INPUT_SMOOTHING_SUPPORTED
512
if (cinfo->smoothing_factor) {
513
downsample->methods[ci] = fullsize_smooth_downsample;
514
downsample->pub.need_context_rows = TRUE;
517
downsample->methods[ci] = fullsize_downsample;
518
} else if (h_in_group == h_out_group * 2 &&
519
v_in_group == v_out_group) {
521
downsample->methods[ci] = h2v1_downsample;
522
} else if (h_in_group == h_out_group * 2 &&
523
v_in_group == v_out_group * 2) {
524
#ifdef INPUT_SMOOTHING_SUPPORTED
525
if (cinfo->smoothing_factor) {
526
downsample->methods[ci] = h2v2_smooth_downsample;
527
downsample->pub.need_context_rows = TRUE;
530
downsample->methods[ci] = h2v2_downsample;
531
} else if ((h_in_group % h_out_group) == 0 &&
532
(v_in_group % v_out_group) == 0) {
534
downsample->methods[ci] = int_downsample;
535
downsample->h_expand[ci] = (UINT8) (h_in_group / h_out_group);
536
downsample->v_expand[ci] = (UINT8) (v_in_group / v_out_group);
538
ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
541
#ifdef INPUT_SMOOTHING_SUPPORTED
542
if (cinfo->smoothing_factor && !smoothok)
543
TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
added
removed
jpg/jcsample.c
