1/*
2 * jcsample.c
3 *
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.
7 *
8 * This file contains downsampling routines.
9 *
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.
14 *
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.
20 *
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.
26 *
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.
30 *
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.
38 *
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.
46 */
47
48#define JPEG_INTERNALS
49#include "jinclude.h"
50#include "jpeglib.h"
51
52
53/* Pointer to routine to downsample a single component */
54typedef JMETHOD(void, downsample1_ptr,
55 (j_compress_ptr cinfo, jpeg_component_info * compptr,
56 JSAMPARRAY input_data, JSAMPARRAY output_data));
57
58/* Private subobject */
59
60typedef struct {
61 struct jpeg_downsampler pub; /* public fields */
62
63 /* Downsampling method pointers, one per component */
64 downsample1_ptr methods[MAX_COMPONENTS];
65} my_downsampler;
66
67typedef my_downsampler * my_downsample_ptr;
68
69
70/*
71 * Initialize for a downsampling pass.
72 */
73
74METHODDEF(void)
75start_pass_downsample (j_compress_ptr cinfo)
76{
77 /* no work for now */
78}
79
80
81/*
82 * Expand a component horizontally from width input_cols to width output_cols,
83 * by duplicating the rightmost samples.
84 */
85
86LOCAL(void)
87expand_right_edge (JSAMPARRAY image_data, int num_rows,
88 JDIMENSION input_cols, JDIMENSION output_cols)
89{
90 register JSAMPROW ptr;
91 register JSAMPLE pixval;
92 register int count;
93 int row;
94 int numcols = (int) (output_cols - input_cols);
95
96 if (numcols > 0) {
97 for (row = 0; row < num_rows; row++) {
98 ptr = image_data[row] + input_cols;
99 pixval = ptr[-1]; /* don't need GETJSAMPLE() here */
100 for (count = numcols; count > 0; count--)
101 *ptr++ = pixval;
102 }
103 }
104}
105
106
107/*
108 * Do downsampling for a whole row group (all components).
109 *
110 * In this version we simply downsample each component independently.
111 */
112
113METHODDEF(void)
114sep_downsample (j_compress_ptr cinfo,
115 JSAMPIMAGE input_buf, JDIMENSION in_row_index,
116 JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
117{
118 my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
119 int ci;
120 jpeg_component_info * compptr;
121 JSAMPARRAY in_ptr, out_ptr;
122
123 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
124 ci++, compptr++) {
125 in_ptr = input_buf[ci] + in_row_index;
126 out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
127 (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
128 }
129}
130
131
132/*
133 * Downsample pixel values of a single component.
134 * One row group is processed per call.
135 * This version handles arbitrary integral sampling ratios, without smoothing.
136 * Note that this version is not actually used for customary sampling ratios.
137 */
138
139METHODDEF(void)
140int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
141 JSAMPARRAY input_data, JSAMPARRAY output_data)
142{
143 int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
144 JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */
145 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
146 JSAMPROW inptr, outptr;
147 INT32 outvalue;
148
149 h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
150 v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
151 numpix = h_expand * v_expand;
152 numpix2 = numpix/2;
153
154 /* Expand input data enough to let all the output samples be generated
155 * by the standard loop. Special-casing padded output would be more
156 * efficient.
157 */
158 expand_right_edge(input_data, cinfo->max_v_samp_factor,
159 cinfo->image_width, output_cols * h_expand);
160
161 inrow = 0;
162 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
163 outptr = output_data[outrow];
164 for (outcol = 0, outcol_h = 0; outcol < output_cols;
165 outcol++, outcol_h += h_expand) {
166 outvalue = 0;
167 for (v = 0; v < v_expand; v++) {
168 inptr = input_data[inrow+v] + outcol_h;
169 for (h = 0; h < h_expand; h++) {
170 outvalue += (INT32) GETJSAMPLE(*inptr++);
171 }
172 }
173 *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
174 }
175 inrow += v_expand;
176 }
177}
178
179
180/*
181 * Downsample pixel values of a single component.
182 * This version handles the special case of a full-size component,
183 * without smoothing.
184 */
185
186METHODDEF(void)
187fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
188 JSAMPARRAY input_data, JSAMPARRAY output_data)
189{
190 /* Copy the data */
191 jcopy_sample_rows(input_data, 0, output_data, 0,
192 cinfo->max_v_samp_factor, cinfo->image_width);
193 /* Edge-expand */
194 expand_right_edge(output_data, cinfo->max_v_samp_factor,
195 cinfo->image_width, compptr->width_in_blocks * DCTSIZE);
196}
197
198
199/*
200 * Downsample pixel values of a single component.
201 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
202 * without smoothing.
203 *
204 * A note about the "bias" calculations: when rounding fractional values to
205 * integer, we do not want to always round 0.5 up to the next integer.
206 * If we did that, we'd introduce a noticeable bias towards larger values.
207 * Instead, this code is arranged so that 0.5 will be rounded up or down at
208 * alternate pixel locations (a simple ordered dither pattern).
209 */
210
211METHODDEF(void)
212h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
213 JSAMPARRAY input_data, JSAMPARRAY output_data)
214{
215 int outrow;
216 JDIMENSION outcol;
217 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
218 register JSAMPROW inptr, outptr;
219 register int bias;
220
221 /* Expand input data enough to let all the output samples be generated
222 * by the standard loop. Special-casing padded output would be more
223 * efficient.
224 */
225 expand_right_edge(input_data, cinfo->max_v_samp_factor,
226 cinfo->image_width, output_cols * 2);
227
228 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
229 outptr = output_data[outrow];
230 inptr = input_data[outrow];
231 bias = 0; /* bias = 0,1,0,1,... for successive samples */
232 for (outcol = 0; outcol < output_cols; outcol++) {
233 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
234 + bias) >> 1);
235 bias ^= 1; /* 0=>1, 1=>0 */
236 inptr += 2;
237 }
238 }
239}
240
241
242/*
243 * Downsample pixel values of a single component.
244 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
245 * without smoothing.
246 */
247
248METHODDEF(void)
249h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
250 JSAMPARRAY input_data, JSAMPARRAY output_data)
251{
252 int inrow, outrow;
253 JDIMENSION outcol;
254 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
255 register JSAMPROW inptr0, inptr1, outptr;
256 register int bias;
257
258 /* Expand input data enough to let all the output samples be generated
259 * by the standard loop. Special-casing padded output would be more
260 * efficient.
261 */
262 expand_right_edge(input_data, cinfo->max_v_samp_factor,
263 cinfo->image_width, output_cols * 2);
264
265 inrow = 0;
266 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
267 outptr = output_data[outrow];
268 inptr0 = input_data[inrow];
269 inptr1 = input_data[inrow+1];
270 bias = 1; /* bias = 1,2,1,2,... for successive samples */
271 for (outcol = 0; outcol < output_cols; outcol++) {
272 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
273 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
274 + bias) >> 2);
275 bias ^= 3; /* 1=>2, 2=>1 */
276 inptr0 += 2; inptr1 += 2;
277 }
278 inrow += 2;
279 }
280}
281
282
283#ifdef INPUT_SMOOTHING_SUPPORTED
284
285/*
286 * Downsample pixel values of a single component.
287 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
288 * with smoothing. One row of context is required.
289 */
290
291METHODDEF(void)
292h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
293 JSAMPARRAY input_data, JSAMPARRAY output_data)
294{
295 int inrow, outrow;
296 JDIMENSION colctr;
297 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
298 register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
299 INT32 membersum, neighsum, memberscale, neighscale;
300
301 /* Expand input data enough to let all the output samples be generated
302 * by the standard loop. Special-casing padded output would be more
303 * efficient.
304 */
305 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
306 cinfo->image_width, output_cols * 2);
307
308 /* We don't bother to form the individual "smoothed" input pixel values;
309 * we can directly compute the output which is the average of the four
310 * smoothed values. Each of the four member pixels contributes a fraction
311 * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
312 * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
313 * output. The four corner-adjacent neighbor pixels contribute a fraction
314 * SF to just one smoothed pixel, or SF/4 to the final output; while the
315 * eight edge-adjacent neighbors contribute SF to each of two smoothed
316 * pixels, or SF/2 overall. In order to use integer arithmetic, these
317 * factors are scaled by 2^16 = 65536.
318 * Also recall that SF = smoothing_factor / 1024.
319 */
320
321 memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
322 neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
323
324 inrow = 0;
325 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
326 outptr = output_data[outrow];
327 inptr0 = input_data[inrow];
328 inptr1 = input_data[inrow+1];
329 above_ptr = input_data[inrow-1];
330 below_ptr = input_data[inrow+2];
331
332 /* Special case for first column: pretend column -1 is same as column 0 */
333 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
334 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
335 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
336 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
337 GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
338 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
339 neighsum += neighsum;
340 neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
341 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]);
342 membersum = membersum * memberscale + neighsum * neighscale;
343 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
344 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
345
346 for (colctr = output_cols - 2; colctr > 0; colctr--) {
347 /* sum of pixels directly mapped to this output element */
348 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
349 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
350 /* sum of edge-neighbor pixels */
351 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
352 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
353 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
354 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
355 /* The edge-neighbors count twice as much as corner-neighbors */
356 neighsum += neighsum;
357 /* Add in the corner-neighbors */
358 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
359 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
360 /* form final output scaled up by 2^16 */
361 membersum = membersum * memberscale + neighsum * neighscale;
362 /* round, descale and output it */
363 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
364 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
365 }
366
367 /* Special case for last column */
368 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
369 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
370 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
371 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
372 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
373 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
374 neighsum += neighsum;
375 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
376 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
377 membersum = membersum * memberscale + neighsum * neighscale;
378 *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
379
380 inrow += 2;
381 }
382}
383
384
385/*
386 * Downsample pixel values of a single component.
387 * This version handles the special case of a full-size component,
388 * with smoothing. One row of context is required.
389 */
390
391METHODDEF(void)
392fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
393 JSAMPARRAY input_data, JSAMPARRAY output_data)
394{
395 int outrow;
396 JDIMENSION colctr;
397 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
398 register JSAMPROW inptr, above_ptr, below_ptr, outptr;
399 INT32 membersum, neighsum, memberscale, neighscale;
400 int colsum, lastcolsum, nextcolsum;
401
402 /* Expand input data enough to let all the output samples be generated
403 * by the standard loop. Special-casing padded output would be more
404 * efficient.
405 */
406 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
407 cinfo->image_width, output_cols);
408
409 /* Each of the eight neighbor pixels contributes a fraction SF to the
410 * smoothed pixel, while the main pixel contributes (1-8*SF). In order
411 * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
412 * Also recall that SF = smoothing_factor / 1024.
413 */
414
415 memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
416 neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
417
418 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
419 outptr = output_data[outrow];
420 inptr = input_data[outrow];
421 above_ptr = input_data[outrow-1];
422 below_ptr = input_data[outrow+1];
423
424 /* Special case for first column */
425 colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
426 GETJSAMPLE(*inptr);
427 membersum = GETJSAMPLE(*inptr++);
428 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
429 GETJSAMPLE(*inptr);
430 neighsum = colsum + (colsum - membersum) + nextcolsum;
431 membersum = membersum * memberscale + neighsum * neighscale;
432 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
433 lastcolsum = colsum; colsum = nextcolsum;
434
435 for (colctr = output_cols - 2; colctr > 0; colctr--) {
436 membersum = GETJSAMPLE(*inptr++);
437 above_ptr++; below_ptr++;
438 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
439 GETJSAMPLE(*inptr);
440 neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
441 membersum = membersum * memberscale + neighsum * neighscale;
442 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
443 lastcolsum = colsum; colsum = nextcolsum;
444 }
445
446 /* Special case for last column */
447 membersum = GETJSAMPLE(*inptr);
448 neighsum = lastcolsum + (colsum - membersum) + colsum;
449 membersum = membersum * memberscale + neighsum * neighscale;
450 *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
451
452 }
453}
454
455#endif /* INPUT_SMOOTHING_SUPPORTED */
456
457
458/*
459 * Module initialization routine for downsampling.
460 * Note that we must select a routine for each component.
461 */
462
463GLOBAL(void)
464jinit_downsampler (j_compress_ptr cinfo)
465{
466 my_downsample_ptr downsample;
467 int ci;
468 jpeg_component_info * compptr;
469 boolean smoothok = TRUE;
470
471 downsample = (my_downsample_ptr)
472 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
473 SIZEOF(my_downsampler));
474 cinfo->downsample = (struct jpeg_downsampler *) downsample;
475 downsample->pub.start_pass = start_pass_downsample;
476 downsample->pub.downsample = sep_downsample;
477 downsample->pub.need_context_rows = FALSE;
478
479 if (cinfo->CCIR601_sampling)
480 ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
481
482 /* Verify we can handle the sampling factors, and set up method pointers */
483 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
484 ci++, compptr++) {
485 if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
486 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
487#ifdef INPUT_SMOOTHING_SUPPORTED
488 if (cinfo->smoothing_factor) {
489 downsample->methods[ci] = fullsize_smooth_downsample;
490 downsample->pub.need_context_rows = TRUE;
491 } else
492#endif
493 downsample->methods[ci] = fullsize_downsample;
494 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
495 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
496 smoothok = FALSE;
497 downsample->methods[ci] = h2v1_downsample;
498 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
499 compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
500#ifdef INPUT_SMOOTHING_SUPPORTED
501 if (cinfo->smoothing_factor) {
502 downsample->methods[ci] = h2v2_smooth_downsample;
503 downsample->pub.need_context_rows = TRUE;
504 } else
505#endif
506 downsample->methods[ci] = h2v2_downsample;
507 } else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
508 (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
509 smoothok = FALSE;
510 downsample->methods[ci] = int_downsample;
511 } else
512 ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
513 }
514
515#ifdef INPUT_SMOOTHING_SUPPORTED
516 if (cinfo->smoothing_factor && !smoothok)
517 TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
518#endif
519}
520