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 */
54 typedef 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
60 typedef struct {
61 struct jpeg_downsampler pub; /* public fields */
62
63 /* Downsampling method pointers, one per component */
64 downsample1_ptr methods[MAX_COMPONENTS];
65
66 /* Height of an output row group for each component. */
67 int rowgroup_height[MAX_COMPONENTS];
68
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.
71 */
72 UINT8 h_expand[MAX_COMPONENTS];
73 UINT8 v_expand[MAX_COMPONENTS];
74 } my_downsampler;
75
76 typedef my_downsampler * my_downsample_ptr;
77
78
79 /*
80 * Initialize for a downsampling pass.
81 */
82
83 METHODDEF(void)
84 start_pass_downsample (j_compress_ptr cinfo)
85 {
86 /* no work for now */
87 }
88
89
90 /*
91 * Expand a component horizontally from width input_cols to width output_cols,
92 * by duplicating the rightmost samples.
93 */
94
95 LOCAL(void)
96 expand_right_edge (JSAMPARRAY image_data, int num_rows,
97 JDIMENSION input_cols, JDIMENSION output_cols)
98 {
99 register JSAMPROW ptr;
100 register JSAMPLE pixval;
101 register int count;
102 int row;
103 int numcols = (int) (output_cols - input_cols);
104
105 if (numcols > 0) {
106 for (row = 0; row < num_rows; row++) {
107 ptr = image_data[row] + input_cols;
108 pixval = ptr[-1]; /* don't need GETJSAMPLE() here */
109 for (count = numcols; count > 0; count--)
110 *ptr++ = pixval;
111 }
112 }
113 }
114
115
116 /*
117 * Do downsampling for a whole row group (all components).
118 *
119 * In this version we simply downsample each component independently.
120 */
121
122 METHODDEF(void)
123 sep_downsample (j_compress_ptr cinfo,
124 JSAMPIMAGE input_buf, JDIMENSION in_row_index,
125 JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
126 {
127 my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
128 int ci;
129 jpeg_component_info * compptr;
130 JSAMPARRAY in_ptr, out_ptr;
131
132 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
133 ci++, compptr++) {
134 in_ptr = input_buf[ci] + in_row_index;
135 out_ptr = output_buf[ci] +
136 (out_row_group_index * downsample->rowgroup_height[ci]);
137 (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
138 }
139 }
140
141
142 /*
143 * Downsample pixel values of a single component.
144 * One row group is processed per call.
145 * This version handles arbitrary integral sampling ratios, without smoothing.
146 * Note that this version is not actually used for customary sampling ratios.
147 */
148
149 METHODDEF(void)
150 int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
151 JSAMPARRAY input_data, JSAMPARRAY output_data)
152 {
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;
158 INT32 outvalue;
159
160 h_expand = downsample->h_expand[compptr->component_index];
161 v_expand = downsample->v_expand[compptr->component_index];
162 numpix = h_expand * v_expand;
163 numpix2 = numpix/2;
164
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
167 * efficient.
168 */
169 expand_right_edge(input_data, cinfo->max_v_samp_factor,
170 cinfo->image_width, output_cols * h_expand);
171
172 inrow = outrow = 0;
173 while (inrow < cinfo->max_v_samp_factor) {
174 outptr = output_data[outrow];
175 for (outcol = 0, outcol_h = 0; outcol < output_cols;
176 outcol++, outcol_h += h_expand) {
177 outvalue = 0;
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++);
182 }
183 }
184 *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
185 }
186 inrow += v_expand;
187 outrow++;
188 }
189 }
190
191
192 /*
193 * Downsample pixel values of a single component.
194 * This version handles the special case of a full-size component,
195 * without smoothing.
196 */
197
198 METHODDEF(void)
199 fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
200 JSAMPARRAY input_data, JSAMPARRAY output_data)
201 {
202 /* Copy the data */
203 jcopy_sample_rows(input_data, 0, output_data, 0,
204 cinfo->max_v_samp_factor, cinfo->image_width);
205 /* Edge-expand */
206 expand_right_edge(output_data, cinfo->max_v_samp_factor, cinfo->image_width,
207 compptr->width_in_blocks * compptr->DCT_h_scaled_size);
208 }
209
210
211 /*
212 * Downsample pixel values of a single component.
213 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
214 * without smoothing.
215 *
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).
221 */
222
223 METHODDEF(void)
224 h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
225 JSAMPARRAY input_data, JSAMPARRAY output_data)
226 {
227 int inrow;
228 JDIMENSION outcol;
229 JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
230 register JSAMPROW inptr, outptr;
231 register int bias;
232
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
235 * efficient.
236 */
237 expand_right_edge(input_data, cinfo->max_v_samp_factor,
238 cinfo->image_width, output_cols * 2);
239
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])
246 + bias) >> 1);
247 bias ^= 1; /* 0=>1, 1=>0 */
248 inptr += 2;
249 }
250 }
251 }
252
253
254 /*
255 * Downsample pixel values of a single component.
256 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
257 * without smoothing.
258 */
259
260 METHODDEF(void)
261 h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
262 JSAMPARRAY input_data, JSAMPARRAY output_data)
263 {
264 int inrow, outrow;
265 JDIMENSION outcol;
266 JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
267 register JSAMPROW inptr0, inptr1, outptr;
268 register int bias;
269
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
272 * efficient.
273 */
274 expand_right_edge(input_data, cinfo->max_v_samp_factor,
275 cinfo->image_width, output_cols * 2);
276
277 inrow = outrow = 0;
278 while (inrow < cinfo->max_v_samp_factor) {
279 outptr = output_data[outrow];
280 inptr0 = input_data[inrow];
281 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]) +
285 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
286 + bias) >> 2);
287 bias ^= 3; /* 1=>2, 2=>1 */
288 inptr0 += 2; inptr1 += 2;
289 }
290 inrow += 2;
291 outrow++;
292 }
293 }
294
295
296 #ifdef INPUT_SMOOTHING_SUPPORTED
297
298 /*
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.
302 */
303
304 METHODDEF(void)
305 h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
306 JSAMPARRAY input_data, JSAMPARRAY output_data)
307 {
308 int inrow, outrow;
309 JDIMENSION colctr;
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;
313
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
316 * efficient.
317 */
318 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
319 cinfo->image_width, output_cols * 2);
320
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
328 * eight edge-adjacent neighbors contribute SF to each of two smoothed
329 * 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.
332 */
333
334 memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
335 neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
336
337 inrow = outrow = 0;
338 while (inrow < cinfo->max_v_samp_factor) {
339 outptr = output_data[outrow];
340 inptr0 = input_data[inrow];
341 inptr1 = input_data[inrow+1];
342 above_ptr = input_data[inrow-1];
343 below_ptr = input_data[inrow+2];
344
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;
358
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;
378 }
379
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);
392
393 inrow += 2;
394 outrow++;
395 }
396 }
397
398
399 /*
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.
403 */
404
405 METHODDEF(void)
406 fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
407 JSAMPARRAY input_data, JSAMPARRAY output_data)
408 {
409 int inrow;
410 JDIMENSION colctr;
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;
415
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
418 * efficient.
419 */
420 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
421 cinfo->image_width, output_cols);
422
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.
427 */
428
429 memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
430 neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
431
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];
437
438 /* Special case for first column */
439 colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
440 GETJSAMPLE(*inptr);
441 membersum = GETJSAMPLE(*inptr++);
442 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
443 GETJSAMPLE(*inptr);
444 neighsum = colsum + (colsum - membersum) + nextcolsum;
445 membersum = membersum * memberscale + neighsum * neighscale;
446 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
447 lastcolsum = colsum; colsum = nextcolsum;
448
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) +
453 GETJSAMPLE(*inptr);
454 neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
455 membersum = membersum * memberscale + neighsum * neighscale;
456 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
457 lastcolsum = colsum; colsum = nextcolsum;
458 }
459
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);
465
466 }
467 }
468
469 #endif /* INPUT_SMOOTHING_SUPPORTED */
470
471
472 /*
473 * Module initialization routine for downsampling.
474 * Note that we must select a routine for each component.
475 */
476
477 GLOBAL(void)
478 jinit_downsampler (j_compress_ptr cinfo)
479 {
480 my_downsample_ptr downsample;
481 int ci;
482 jpeg_component_info * compptr;
483 boolean smoothok = TRUE;
484 int h_in_group, v_in_group, h_out_group, v_out_group;
485
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;
493
494 if (cinfo->CCIR601_sampling)
495 ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
496
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;
499 ci++, compptr++) {
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.
502 */
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;
515 } else
516 #endif
517 downsample->methods[ci] = fullsize_downsample;
518 } else if (h_in_group == h_out_group * 2 &&
519 v_in_group == v_out_group) {
520 smoothok = FALSE;
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;
528 } else
529 #endif
530 downsample->methods[ci] = h2v2_downsample;
531 } else if ((h_in_group % h_out_group) == 0 &&
532 (v_in_group % v_out_group) == 0) {
533 smoothok = FALSE;
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);
537 } else
538 ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
539 }
540
541 #ifdef INPUT_SMOOTHING_SUPPORTED
542 if (cinfo->smoothing_factor && !smoothok)
543 TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
544 #endif
545 }