1/*
2 * reserved comment block
3 * DO NOT REMOVE OR ALTER!
4 */
5/*
6 * jcsample.c
7 *
8 * Copyright (C) 1991-1996, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
10 * For conditions of distribution and use, see the accompanying README file.
11 *
12 * This file contains downsampling routines.
13 *
14 * Downsampling input data is counted in "row groups". A row group
15 * is defined to be max_v_samp_factor pixel rows of each component,
16 * from which the downsampler produces v_samp_factor sample rows.
17 * A single row group is processed in each call to the downsampler module.
18 *
19 * The downsampler is responsible for edge-expansion of its output data
20 * to fill an integral number of DCT blocks horizontally. The source buffer
21 * may be modified if it is helpful for this purpose (the source buffer is
22 * allocated wide enough to correspond to the desired output width).
23 * The caller (the prep controller) is responsible for vertical padding.
24 *
25 * The downsampler may request "context rows" by setting need_context_rows
26 * during startup. In this case, the input arrays will contain at least
27 * one row group's worth of pixels above and below the passed-in data;
28 * the caller will create dummy rows at image top and bottom by replicating
29 * the first or last real pixel row.
30 *
31 * An excellent reference for image resampling is
32 * Digital Image Warping, George Wolberg, 1990.
33 * Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
34 *
35 * The downsampling algorithm used here is a simple average of the source
36 * pixels covered by the output pixel. The hi-falutin sampling literature
37 * refers to this as a "box filter". In general the characteristics of a box
38 * filter are not very good, but for the specific cases we normally use (1:1
39 * and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
40 * nearly so bad. If you intend to use other sampling ratios, you'd be well
41 * advised to improve this code.
42 *
43 * A simple input-smoothing capability is provided. This is mainly intended
44 * for cleaning up color-dithered GIF input files (if you find it inadequate,
45 * we suggest using an external filtering program such as pnmconvol). When
46 * enabled, each input pixel P is replaced by a weighted sum of itself and its
47 * eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF,
48 * where SF = (smoothing_factor / 1024).
49 * Currently, smoothing is only supported for 2h2v sampling factors.
50 */
51
52#define JPEG_INTERNALS
53#include "jinclude.h"
54#include "jpeglib.h"
55
56
57/* Pointer to routine to downsample a single component */
58typedef JMETHOD(void, downsample1_ptr,
59 (j_compress_ptr cinfo, jpeg_component_info * compptr,
60 JSAMPARRAY input_data, JSAMPARRAY output_data));
61
62/* Private subobject */
63
64typedef struct {
65 struct jpeg_downsampler pub; /* public fields */
66
67 /* Downsampling method pointers, one per component */
68 downsample1_ptr methods[MAX_COMPONENTS];
69} my_downsampler;
70
71typedef my_downsampler * my_downsample_ptr;
72
73
74/*
75 * Initialize for a downsampling pass.
76 */
77
78METHODDEF(void)
79start_pass_downsample (j_compress_ptr cinfo)
80{
81 /* no work for now */
82}
83
84
85/*
86 * Expand a component horizontally from width input_cols to width output_cols,
87 * by duplicating the rightmost samples.
88 */
89
90LOCAL(void)
91expand_right_edge (JSAMPARRAY image_data, int num_rows,
92 JDIMENSION input_cols, JDIMENSION output_cols)
93{
94 register JSAMPROW ptr;
95 register JSAMPLE pixval;
96 register int count;
97 int row;
98 int numcols = (int) (output_cols - input_cols);
99
100 if (numcols > 0) {
101 for (row = 0; row < num_rows; row++) {
102 ptr = image_data[row] + input_cols;
103 pixval = ptr[-1]; /* don't need GETJSAMPLE() here */
104 for (count = numcols; count > 0; count--)
105 *ptr++ = pixval;
106 }
107 }
108}
109
110
111/*
112 * Do downsampling for a whole row group (all components).
113 *
114 * In this version we simply downsample each component independently.
115 */
116
117METHODDEF(void)
118sep_downsample (j_compress_ptr cinfo,
119 JSAMPIMAGE input_buf, JDIMENSION in_row_index,
120 JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
121{
122 my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
123 int ci;
124 jpeg_component_info * compptr;
125 JSAMPARRAY in_ptr, out_ptr;
126
127 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
128 ci++, compptr++) {
129 in_ptr = input_buf[ci] + in_row_index;
130 out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
131 (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
132 }
133}
134
135
136/*
137 * Downsample pixel values of a single component.
138 * One row group is processed per call.
139 * This version handles arbitrary integral sampling ratios, without smoothing.
140 * Note that this version is not actually used for customary sampling ratios.
141 */
142
143METHODDEF(void)
144int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
145 JSAMPARRAY input_data, JSAMPARRAY output_data)
146{
147 int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
148 JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */
149 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
150 JSAMPROW inptr, outptr;
151 INT32 outvalue;
152
153 h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
154 v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
155 numpix = h_expand * v_expand;
156 numpix2 = numpix/2;
157
158 /* Expand input data enough to let all the output samples be generated
159 * by the standard loop. Special-casing padded output would be more
160 * efficient.
161 */
162 expand_right_edge(input_data, cinfo->max_v_samp_factor,
163 cinfo->image_width, output_cols * h_expand);
164
165 inrow = 0;
166 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
167 outptr = output_data[outrow];
168 for (outcol = 0, outcol_h = 0; outcol < output_cols;
169 outcol++, outcol_h += h_expand) {
170 outvalue = 0;
171 for (v = 0; v < v_expand; v++) {
172 inptr = input_data[inrow+v] + outcol_h;
173 for (h = 0; h < h_expand; h++) {
174 outvalue += (INT32) GETJSAMPLE(*inptr++);
175 }
176 }
177 *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
178 }
179 inrow += v_expand;
180 }
181}
182
183
184/*
185 * Downsample pixel values of a single component.
186 * This version handles the special case of a full-size component,
187 * without smoothing.
188 */
189
190METHODDEF(void)
191fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
192 JSAMPARRAY input_data, JSAMPARRAY output_data)
193{
194 /* Copy the data */
195 jcopy_sample_rows(input_data, 0, output_data, 0,
196 cinfo->max_v_samp_factor, cinfo->image_width);
197 /* Edge-expand */
198 expand_right_edge(output_data, cinfo->max_v_samp_factor,
199 cinfo->image_width, compptr->width_in_blocks * DCTSIZE);
200}
201
202
203/*
204 * Downsample pixel values of a single component.
205 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
206 * without smoothing.
207 *
208 * A note about the "bias" calculations: when rounding fractional values to
209 * integer, we do not want to always round 0.5 up to the next integer.
210 * If we did that, we'd introduce a noticeable bias towards larger values.
211 * Instead, this code is arranged so that 0.5 will be rounded up or down at
212 * alternate pixel locations (a simple ordered dither pattern).
213 */
214
215METHODDEF(void)
216h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
217 JSAMPARRAY input_data, JSAMPARRAY output_data)
218{
219 int outrow;
220 JDIMENSION outcol;
221 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
222 register JSAMPROW inptr, outptr;
223 register int bias;
224
225 /* Expand input data enough to let all the output samples be generated
226 * by the standard loop. Special-casing padded output would be more
227 * efficient.
228 */
229 expand_right_edge(input_data, cinfo->max_v_samp_factor,
230 cinfo->image_width, output_cols * 2);
231
232 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
233 outptr = output_data[outrow];
234 inptr = input_data[outrow];
235 bias = 0; /* bias = 0,1,0,1,... for successive samples */
236 for (outcol = 0; outcol < output_cols; outcol++) {
237 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
238 + bias) >> 1);
239 bias ^= 1; /* 0=>1, 1=>0 */
240 inptr += 2;
241 }
242 }
243}
244
245
246/*
247 * Downsample pixel values of a single component.
248 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
249 * without smoothing.
250 */
251
252METHODDEF(void)
253h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
254 JSAMPARRAY input_data, JSAMPARRAY output_data)
255{
256 int inrow, outrow;
257 JDIMENSION outcol;
258 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
259 register JSAMPROW inptr0, inptr1, outptr;
260 register int bias;
261
262 /* Expand input data enough to let all the output samples be generated
263 * by the standard loop. Special-casing padded output would be more
264 * efficient.
265 */
266 expand_right_edge(input_data, cinfo->max_v_samp_factor,
267 cinfo->image_width, output_cols * 2);
268
269 inrow = 0;
270 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
271 outptr = output_data[outrow];
272 inptr0 = input_data[inrow];
273 inptr1 = input_data[inrow+1];
274 bias = 1; /* bias = 1,2,1,2,... for successive samples */
275 for (outcol = 0; outcol < output_cols; outcol++) {
276 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
277 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
278 + bias) >> 2);
279 bias ^= 3; /* 1=>2, 2=>1 */
280 inptr0 += 2; inptr1 += 2;
281 }
282 inrow += 2;
283 }
284}
285
286
287#ifdef INPUT_SMOOTHING_SUPPORTED
288
289/*
290 * Downsample pixel values of a single component.
291 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
292 * with smoothing. One row of context is required.
293 */
294
295METHODDEF(void)
296h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
297 JSAMPARRAY input_data, JSAMPARRAY output_data)
298{
299 int inrow, outrow;
300 JDIMENSION colctr;
301 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
302 register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
303 INT32 membersum, neighsum, memberscale, neighscale;
304
305 /* Expand input data enough to let all the output samples be generated
306 * by the standard loop. Special-casing padded output would be more
307 * efficient.
308 */
309 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
310 cinfo->image_width, output_cols * 2);
311
312 /* We don't bother to form the individual "smoothed" input pixel values;
313 * we can directly compute the output which is the average of the four
314 * smoothed values. Each of the four member pixels contributes a fraction
315 * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
316 * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
317 * output. The four corner-adjacent neighbor pixels contribute a fraction
318 * SF to just one smoothed pixel, or SF/4 to the final output; while the
319 * eight edge-adjacent neighbors contribute SF to each of two smoothed
320 * pixels, or SF/2 overall. In order to use integer arithmetic, these
321 * factors are scaled by 2^16 = 65536.
322 * Also recall that SF = smoothing_factor / 1024.
323 */
324
325 memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
326 neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
327
328 inrow = 0;
329 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
330 outptr = output_data[outrow];
331 inptr0 = input_data[inrow];
332 inptr1 = input_data[inrow+1];
333 above_ptr = input_data[inrow-1];
334 below_ptr = input_data[inrow+2];
335
336 /* Special case for first column: pretend column -1 is same as column 0 */
337 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
338 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
339 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
340 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
341 GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
342 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
343 neighsum += neighsum;
344 neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
345 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]);
346 membersum = membersum * memberscale + neighsum * neighscale;
347 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
348 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
349
350 for (colctr = output_cols - 2; colctr > 0; colctr--) {
351 /* sum of pixels directly mapped to this output element */
352 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
353 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
354 /* sum of edge-neighbor pixels */
355 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
356 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
357 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
358 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
359 /* The edge-neighbors count twice as much as corner-neighbors */
360 neighsum += neighsum;
361 /* Add in the corner-neighbors */
362 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
363 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
364 /* form final output scaled up by 2^16 */
365 membersum = membersum * memberscale + neighsum * neighscale;
366 /* round, descale and output it */
367 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
368 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
369 }
370
371 /* Special case for last column */
372 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
373 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
374 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
375 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
376 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
377 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
378 neighsum += neighsum;
379 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
380 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
381 membersum = membersum * memberscale + neighsum * neighscale;
382 *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
383
384 inrow += 2;
385 }
386}
387
388
389/*
390 * Downsample pixel values of a single component.
391 * This version handles the special case of a full-size component,
392 * with smoothing. One row of context is required.
393 */
394
395METHODDEF(void)
396fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
397 JSAMPARRAY input_data, JSAMPARRAY output_data)
398{
399 int outrow;
400 JDIMENSION colctr;
401 JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
402 register JSAMPROW inptr, above_ptr, below_ptr, outptr;
403 INT32 membersum, neighsum, memberscale, neighscale;
404 int colsum, lastcolsum, nextcolsum;
405
406 /* Expand input data enough to let all the output samples be generated
407 * by the standard loop. Special-casing padded output would be more
408 * efficient.
409 */
410 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
411 cinfo->image_width, output_cols);
412
413 /* Each of the eight neighbor pixels contributes a fraction SF to the
414 * smoothed pixel, while the main pixel contributes (1-8*SF). In order
415 * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
416 * Also recall that SF = smoothing_factor / 1024.
417 */
418
419 memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
420 neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
421
422 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
423 outptr = output_data[outrow];
424 inptr = input_data[outrow];
425 above_ptr = input_data[outrow-1];
426 below_ptr = input_data[outrow+1];
427
428 /* Special case for first column */
429 colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
430 GETJSAMPLE(*inptr);
431 membersum = GETJSAMPLE(*inptr++);
432 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
433 GETJSAMPLE(*inptr);
434 neighsum = colsum + (colsum - membersum) + nextcolsum;
435 membersum = membersum * memberscale + neighsum * neighscale;
436 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
437 lastcolsum = colsum; colsum = nextcolsum;
438
439 for (colctr = output_cols - 2; colctr > 0; colctr--) {
440 membersum = GETJSAMPLE(*inptr++);
441 above_ptr++; below_ptr++;
442 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
443 GETJSAMPLE(*inptr);
444 neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
445 membersum = membersum * memberscale + neighsum * neighscale;
446 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
447 lastcolsum = colsum; colsum = nextcolsum;
448 }
449
450 /* Special case for last column */
451 membersum = GETJSAMPLE(*inptr);
452 neighsum = lastcolsum + (colsum - membersum) + colsum;
453 membersum = membersum * memberscale + neighsum * neighscale;
454 *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
455
456 }
457}
458
459#endif /* INPUT_SMOOTHING_SUPPORTED */
460
461
462/*
463 * Module initialization routine for downsampling.
464 * Note that we must select a routine for each component.
465 */
466
467GLOBAL(void)
468jinit_downsampler (j_compress_ptr cinfo)
469{
470 my_downsample_ptr downsample;
471 int ci;
472 jpeg_component_info * compptr;
473 boolean smoothok = TRUE;
474
475 downsample = (my_downsample_ptr)
476 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
477 SIZEOF(my_downsampler));
478 cinfo->downsample = (struct jpeg_downsampler *) downsample;
479 downsample->pub.start_pass = start_pass_downsample;
480 downsample->pub.downsample = sep_downsample;
481 downsample->pub.need_context_rows = FALSE;
482
483 if (cinfo->CCIR601_sampling)
484 ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
485
486 /* Verify we can handle the sampling factors, and set up method pointers */
487 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
488 ci++, compptr++) {
489 if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
490 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
491#ifdef INPUT_SMOOTHING_SUPPORTED
492 if (cinfo->smoothing_factor) {
493 downsample->methods[ci] = fullsize_smooth_downsample;
494 downsample->pub.need_context_rows = TRUE;
495 } else
496#endif
497 downsample->methods[ci] = fullsize_downsample;
498 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
499 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
500 smoothok = FALSE;
501 downsample->methods[ci] = h2v1_downsample;
502 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
503 compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
504#ifdef INPUT_SMOOTHING_SUPPORTED
505 if (cinfo->smoothing_factor) {
506 downsample->methods[ci] = h2v2_smooth_downsample;
507 downsample->pub.need_context_rows = TRUE;
508 } else
509#endif
510 downsample->methods[ci] = h2v2_downsample;
511 } else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
512 (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
513 smoothok = FALSE;
514 downsample->methods[ci] = int_downsample;
515 } else
516 ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
517 }
518
519#ifdef INPUT_SMOOTHING_SUPPORTED
520 if (cinfo->smoothing_factor && !smoothok)
521 TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
522#endif
523}
524