1/*
2 * jcsample.c
3 *
4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1991-1996, Thomas G. Lane.
6 * libjpeg-turbo Modifications:
7 * Copyright 2009 Pierre Ossman <[email protected]> for Cendio AB
8 * Copyright (C) 2014, MIPS Technologies, Inc., California.
9 * Copyright (C) 2015, 2019, D. R. Commander.
10 * For conditions of distribution and use, see the accompanying README.ijg
11 * file.
12 *
13 * This file contains downsampling routines.
14 *
15 * Downsampling input data is counted in "row groups". A row group
16 * is defined to be max_v_samp_factor pixel rows of each component,
17 * from which the downsampler produces v_samp_factor sample rows.
18 * A single row group is processed in each call to the downsampler module.
19 *
20 * The downsampler is responsible for edge-expansion of its output data
21 * to fill an integral number of DCT blocks horizontally. The source buffer
22 * may be modified if it is helpful for this purpose (the source buffer is
23 * allocated wide enough to correspond to the desired output width).
24 * The caller (the prep controller) is responsible for vertical padding.
25 *
26 * The downsampler may request "context rows" by setting need_context_rows
27 * during startup. In this case, the input arrays will contain at least
28 * one row group's worth of pixels above and below the passed-in data;
29 * the caller will create dummy rows at image top and bottom by replicating
30 * the first or last real pixel row.
31 *
32 * An excellent reference for image resampling is
33 * Digital Image Warping, George Wolberg, 1990.
34 * Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
35 *
36 * The downsampling algorithm used here is a simple average of the source
37 * pixels covered by the output pixel. The hi-falutin sampling literature
38 * refers to this as a "box filter". In general the characteristics of a box
39 * filter are not very good, but for the specific cases we normally use (1:1
40 * and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
41 * nearly so bad. If you intend to use other sampling ratios, you'd be well
42 * advised to improve this code.
43 *
44 * A simple input-smoothing capability is provided. This is mainly intended
45 * for cleaning up color-dithered GIF input files (if you find it inadequate,
46 * we suggest using an external filtering program such as pnmconvol). When
47 * enabled, each input pixel P is replaced by a weighted sum of itself and its
48 * eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF,
49 * where SF = (smoothing_factor / 1024).
50 * Currently, smoothing is only supported for 2h2v sampling factors.
51 */
52
53#define JPEG_INTERNALS
54#include "jinclude.h"
55#include "jpeglib.h"
56#include "jsimd.h"
57
58
59/* Pointer to routine to downsample a single component */
60typedef void (*downsample1_ptr) (j_compress_ptr cinfo,
61 jpeg_component_info *compptr,
62 JSAMPARRAY input_data,
63 JSAMPARRAY output_data);
64
65/* Private subobject */
66
67typedef struct {
68 struct jpeg_downsampler pub; /* public fields */
69
70 /* Downsampling method pointers, one per component */
71 downsample1_ptr methods[MAX_COMPONENTS];
72} my_downsampler;
73
74typedef my_downsampler *my_downsample_ptr;
75
76
77/*
78 * Initialize for a downsampling pass.
79 */
80
81METHODDEF(void)
82start_pass_downsample(j_compress_ptr cinfo)
83{
84 /* no work for now */
85}
86
87
88/*
89 * Expand a component horizontally from width input_cols to width output_cols,
90 * by duplicating the rightmost samples.
91 */
92
93LOCAL(void)
94expand_right_edge(JSAMPARRAY image_data, int num_rows, JDIMENSION input_cols,
95 JDIMENSION output_cols)
96{
97 register JSAMPROW ptr;
98 register JSAMPLE pixval;
99 register int count;
100 int row;
101 int numcols = (int)(output_cols - input_cols);
102
103 if (numcols > 0) {
104 for (row = 0; row < num_rows; row++) {
105 ptr = image_data[row] + input_cols;
106 pixval = ptr[-1];
107 for (count = numcols; count > 0; count--)
108 *ptr++ = pixval;
109 }
110 }
111}
112
113
114/*
115 * Do downsampling for a whole row group (all components).
116 *
117 * In this version we simply downsample each component independently.
118 */
119
120METHODDEF(void)
121sep_downsample(j_compress_ptr cinfo, JSAMPIMAGE input_buf,
122 JDIMENSION in_row_index, JSAMPIMAGE output_buf,
123 JDIMENSION out_row_group_index)
124{
125 my_downsample_ptr downsample = (my_downsample_ptr)cinfo->downsample;
126 int ci;
127 jpeg_component_info *compptr;
128 JSAMPARRAY in_ptr, out_ptr;
129
130 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
131 ci++, compptr++) {
132 in_ptr = input_buf[ci] + in_row_index;
133 out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
134 (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
135 }
136}
137
138
139/*
140 * Downsample pixel values of a single component.
141 * One row group is processed per call.
142 * This version handles arbitrary integral sampling ratios, without smoothing.
143 * Note that this version is not actually used for customary sampling ratios.
144 */
145
146METHODDEF(void)
147int_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
148 JSAMPARRAY input_data, JSAMPARRAY output_data)
149{
150 int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
151 JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */
152 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
153 JSAMPROW inptr, outptr;
154 JLONG outvalue;
155
156 h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
157 v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
158 numpix = h_expand * v_expand;
159 numpix2 = numpix / 2;
160
161 /* Expand input data enough to let all the output samples be generated
162 * by the standard loop. Special-casing padded output would be more
163 * efficient.
164 */
165 expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
166 output_cols * h_expand);
167
168 inrow = 0;
169 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
170 outptr = output_data[outrow];
171 for (outcol = 0, outcol_h = 0; outcol < output_cols;
172 outcol++, outcol_h += h_expand) {
173 outvalue = 0;
174 for (v = 0; v < v_expand; v++) {
175 inptr = input_data[inrow + v] + outcol_h;
176 for (h = 0; h < h_expand; h++) {
177 outvalue += (JLONG)(*inptr++);
178 }
179 }
180 *outptr++ = (JSAMPLE)((outvalue + numpix2) / numpix);
181 }
182 inrow += v_expand;
183 }
184}
185
186
187/*
188 * Downsample pixel values of a single component.
189 * This version handles the special case of a full-size component,
190 * without smoothing.
191 */
192
193METHODDEF(void)
194fullsize_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
195 JSAMPARRAY input_data, JSAMPARRAY output_data)
196{
197 /* Copy the data */
198 jcopy_sample_rows(input_data, 0, output_data, 0, cinfo->max_v_samp_factor,
199 cinfo->image_width);
200 /* Edge-expand */
201 expand_right_edge(output_data, cinfo->max_v_samp_factor, cinfo->image_width,
202 compptr->width_in_blocks * DCTSIZE);
203}
204
205
206/*
207 * Downsample pixel values of a single component.
208 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
209 * without smoothing.
210 *
211 * A note about the "bias" calculations: when rounding fractional values to
212 * integer, we do not want to always round 0.5 up to the next integer.
213 * If we did that, we'd introduce a noticeable bias towards larger values.
214 * Instead, this code is arranged so that 0.5 will be rounded up or down at
215 * alternate pixel locations (a simple ordered dither pattern).
216 */
217
218METHODDEF(void)
219h2v1_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
220 JSAMPARRAY input_data, JSAMPARRAY output_data)
221{
222 int outrow;
223 JDIMENSION outcol;
224 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
225 register JSAMPROW inptr, outptr;
226 register int bias;
227
228 /* Expand input data enough to let all the output samples be generated
229 * by the standard loop. Special-casing padded output would be more
230 * efficient.
231 */
232 expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
233 output_cols * 2);
234
235 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
236 outptr = output_data[outrow];
237 inptr = input_data[outrow];
238 bias = 0; /* bias = 0,1,0,1,... for successive samples */
239 for (outcol = 0; outcol < output_cols; outcol++) {
240 *outptr++ = (JSAMPLE)((inptr[0] + inptr[1] + bias) >> 1);
241 bias ^= 1; /* 0=>1, 1=>0 */
242 inptr += 2;
243 }
244 }
245}
246
247
248/*
249 * Downsample pixel values of a single component.
250 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
251 * without smoothing.
252 */
253
254METHODDEF(void)
255h2v2_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
256 JSAMPARRAY input_data, JSAMPARRAY output_data)
257{
258 int inrow, outrow;
259 JDIMENSION outcol;
260 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
261 register JSAMPROW inptr0, inptr1, outptr;
262 register int bias;
263
264 /* Expand input data enough to let all the output samples be generated
265 * by the standard loop. Special-casing padded output would be more
266 * efficient.
267 */
268 expand_right_edge(input_data, cinfo->max_v_samp_factor, cinfo->image_width,
269 output_cols * 2);
270
271 inrow = 0;
272 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
273 outptr = output_data[outrow];
274 inptr0 = input_data[inrow];
275 inptr1 = input_data[inrow + 1];
276 bias = 1; /* bias = 1,2,1,2,... for successive samples */
277 for (outcol = 0; outcol < output_cols; outcol++) {
278 *outptr++ =
279 (JSAMPLE)((inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1] + bias) >> 2);
280 bias ^= 3; /* 1=>2, 2=>1 */
281 inptr0 += 2; inptr1 += 2;
282 }
283 inrow += 2;
284 }
285}
286
287
288#ifdef INPUT_SMOOTHING_SUPPORTED
289
290/*
291 * Downsample pixel values of a single component.
292 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
293 * with smoothing. One row of context is required.
294 */
295
296METHODDEF(void)
297h2v2_smooth_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
298 JSAMPARRAY input_data, JSAMPARRAY output_data)
299{
300 int inrow, outrow;
301 JDIMENSION colctr;
302 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
303 register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
304 JLONG membersum, neighsum, memberscale, neighscale;
305
306 /* Expand input data enough to let all the output samples be generated
307 * by the standard loop. Special-casing padded output would be more
308 * efficient.
309 */
310 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
311 cinfo->image_width, output_cols * 2);
312
313 /* We don't bother to form the individual "smoothed" input pixel values;
314 * we can directly compute the output which is the average of the four
315 * smoothed values. Each of the four member pixels contributes a fraction
316 * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
317 * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
318 * output. The four corner-adjacent neighbor pixels contribute a fraction
319 * SF to just one smoothed pixel, or SF/4 to the final output; while the
320 * eight edge-adjacent neighbors contribute SF to each of two smoothed
321 * pixels, or SF/2 overall. In order to use integer arithmetic, these
322 * factors are scaled by 2^16 = 65536.
323 * Also recall that SF = smoothing_factor / 1024.
324 */
325
326 memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
327 neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
328
329 inrow = 0;
330 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
331 outptr = output_data[outrow];
332 inptr0 = input_data[inrow];
333 inptr1 = input_data[inrow + 1];
334 above_ptr = input_data[inrow - 1];
335 below_ptr = input_data[inrow + 2];
336
337 /* Special case for first column: pretend column -1 is same as column 0 */
338 membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
339 neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
340 inptr0[0] + inptr0[2] + inptr1[0] + inptr1[2];
341 neighsum += neighsum;
342 neighsum += above_ptr[0] + above_ptr[2] + below_ptr[0] + below_ptr[2];
343 membersum = membersum * memberscale + neighsum * neighscale;
344 *outptr++ = (JSAMPLE)((membersum + 32768) >> 16);
345 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
346
347 for (colctr = output_cols - 2; colctr > 0; colctr--) {
348 /* sum of pixels directly mapped to this output element */
349 membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
350 /* sum of edge-neighbor pixels */
351 neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
352 inptr0[-1] + inptr0[2] + inptr1[-1] + inptr1[2];
353 /* The edge-neighbors count twice as much as corner-neighbors */
354 neighsum += neighsum;
355 /* Add in the corner-neighbors */
356 neighsum += above_ptr[-1] + above_ptr[2] + below_ptr[-1] + below_ptr[2];
357 /* form final output scaled up by 2^16 */
358 membersum = membersum * memberscale + neighsum * neighscale;
359 /* round, descale and output it */
360 *outptr++ = (JSAMPLE)((membersum + 32768) >> 16);
361 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
362 }
363
364 /* Special case for last column */
365 membersum = inptr0[0] + inptr0[1] + inptr1[0] + inptr1[1];
366 neighsum = above_ptr[0] + above_ptr[1] + below_ptr[0] + below_ptr[1] +
367 inptr0[-1] + inptr0[1] + inptr1[-1] + inptr1[1];
368 neighsum += neighsum;
369 neighsum += above_ptr[-1] + above_ptr[1] + below_ptr[-1] + below_ptr[1];
370 membersum = membersum * memberscale + neighsum * neighscale;
371 *outptr = (JSAMPLE)((membersum + 32768) >> 16);
372
373 inrow += 2;
374 }
375}
376
377
378/*
379 * Downsample pixel values of a single component.
380 * This version handles the special case of a full-size component,
381 * with smoothing. One row of context is required.
382 */
383
384METHODDEF(void)
385fullsize_smooth_downsample(j_compress_ptr cinfo, jpeg_component_info *compptr,
386 JSAMPARRAY input_data, JSAMPARRAY output_data)
387{
388 int outrow;
389 JDIMENSION colctr;
390 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
391 register JSAMPROW inptr, above_ptr, below_ptr, outptr;
392 JLONG membersum, neighsum, memberscale, neighscale;
393 int colsum, lastcolsum, nextcolsum;
394
395 /* Expand input data enough to let all the output samples be generated
396 * by the standard loop. Special-casing padded output would be more
397 * efficient.
398 */
399 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
400 cinfo->image_width, output_cols);
401
402 /* Each of the eight neighbor pixels contributes a fraction SF to the
403 * smoothed pixel, while the main pixel contributes (1-8*SF). In order
404 * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
405 * Also recall that SF = smoothing_factor / 1024.
406 */
407
408 memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
409 neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
410
411 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
412 outptr = output_data[outrow];
413 inptr = input_data[outrow];
414 above_ptr = input_data[outrow - 1];
415 below_ptr = input_data[outrow + 1];
416
417 /* Special case for first column */
418 colsum = (*above_ptr++) + (*below_ptr++) + inptr[0];
419 membersum = *inptr++;
420 nextcolsum = above_ptr[0] + below_ptr[0] + inptr[0];
421 neighsum = colsum + (colsum - membersum) + nextcolsum;
422 membersum = membersum * memberscale + neighsum * neighscale;
423 *outptr++ = (JSAMPLE)((membersum + 32768) >> 16);
424 lastcolsum = colsum; colsum = nextcolsum;
425
426 for (colctr = output_cols - 2; colctr > 0; colctr--) {
427 membersum = *inptr++;
428 above_ptr++; below_ptr++;
429 nextcolsum = above_ptr[0] + below_ptr[0] + inptr[0];
430 neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
431 membersum = membersum * memberscale + neighsum * neighscale;
432 *outptr++ = (JSAMPLE)((membersum + 32768) >> 16);
433 lastcolsum = colsum; colsum = nextcolsum;
434 }
435
436 /* Special case for last column */
437 membersum = *inptr;
438 neighsum = lastcolsum + (colsum - membersum) + colsum;
439 membersum = membersum * memberscale + neighsum * neighscale;
440 *outptr = (JSAMPLE)((membersum + 32768) >> 16);
441
442 }
443}
444
445#endif /* INPUT_SMOOTHING_SUPPORTED */
446
447
448/*
449 * Module initialization routine for downsampling.
450 * Note that we must select a routine for each component.
451 */
452
453GLOBAL(void)
454jinit_downsampler(j_compress_ptr cinfo)
455{
456 my_downsample_ptr downsample;
457 int ci;
458 jpeg_component_info *compptr;
459 boolean smoothok = TRUE;
460
461 downsample = (my_downsample_ptr)
462 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
463 sizeof(my_downsampler));
464 cinfo->downsample = (struct jpeg_downsampler *)downsample;
465 downsample->pub.start_pass = start_pass_downsample;
466 downsample->pub.downsample = sep_downsample;
467 downsample->pub.need_context_rows = FALSE;
468
469 if (cinfo->CCIR601_sampling)
470 ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
471
472 /* Verify we can handle the sampling factors, and set up method pointers */
473 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
474 ci++, compptr++) {
475 if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
476 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
477#ifdef INPUT_SMOOTHING_SUPPORTED
478 if (cinfo->smoothing_factor) {
479 downsample->methods[ci] = fullsize_smooth_downsample;
480 downsample->pub.need_context_rows = TRUE;
481 } else
482#endif
483 downsample->methods[ci] = fullsize_downsample;
484 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
485 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
486 smoothok = FALSE;
487 if (jsimd_can_h2v1_downsample())
488 downsample->methods[ci] = jsimd_h2v1_downsample;
489 else
490 downsample->methods[ci] = h2v1_downsample;
491 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
492 compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
493#ifdef INPUT_SMOOTHING_SUPPORTED
494 if (cinfo->smoothing_factor) {
495#if defined(__mips__)
496 if (jsimd_can_h2v2_smooth_downsample())
497 downsample->methods[ci] = jsimd_h2v2_smooth_downsample;
498 else
499#endif
500 downsample->methods[ci] = h2v2_smooth_downsample;
501 downsample->pub.need_context_rows = TRUE;
502 } else
503#endif
504 {
505 if (jsimd_can_h2v2_downsample())
506 downsample->methods[ci] = jsimd_h2v2_downsample;
507 else
508 downsample->methods[ci] = h2v2_downsample;
509 }
510 } else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
511 (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
512 smoothok = FALSE;
513 downsample->methods[ci] = int_downsample;
514 } else
515 ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
516 }
517
518#ifdef INPUT_SMOOTHING_SUPPORTED
519 if (cinfo->smoothing_factor && !smoothok)
520 TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
521#endif
522}
523