4 * Copyright (C) 1991-1998, 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];
67 typedef my_downsampler * my_downsample_ptr;
71 * Initialize for a downsampling pass.
75 start_pass_downsample (j_compress_ptr cinfo)
83 * Expand a component horizontally from width input_cols to width output_cols,
84 * by duplicating the rightmost samples.
88 expand_right_edge (JSAMPARRAY image_data, int num_rows,
89 JDIMENSION input_cols, JDIMENSION output_cols)
91 register JSAMPROW ptr;
92 register JSAMPLE pixval;
95 int numcols = (int) (output_cols - input_cols);
98 for (row = 0; row < num_rows; row++) {
99 ptr = image_data[row] + input_cols;
100 pixval = ptr[-1]; /* don't need GETJSAMPLE() here */
101 for (count = numcols; count > 0; count--)
109 * Do downsampling for a whole row group (all components).
111 * In this version we simply downsample each component independently.
115 sep_downsample (j_compress_ptr cinfo,
116 JSAMPIMAGE input_buf, JDIMENSION in_row_index,
117 JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
119 my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
121 jpeg_component_info * compptr;
122 JSAMPARRAY in_ptr, out_ptr;
124 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
126 in_ptr = input_buf[ci] + in_row_index;
127 out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
128 (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
134 * Downsample pixel values of a single component.
135 * One row group is processed per call.
136 * This version handles arbitrary integral sampling ratios, without smoothing.
137 * Note that this version is not actually used for customary sampling ratios.
141 int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
142 JSAMPARRAY input_data, JSAMPARRAY output_data)
144 int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
145 JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */
146 JDIMENSION output_cols = compptr->width_in_data_units * cinfo->data_unit;
147 JSAMPROW inptr, outptr;
150 h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
151 v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
152 numpix = h_expand * v_expand;
155 /* Expand input data enough to let all the output samples be generated
156 * by the standard loop. Special-casing padded output would be more
159 expand_right_edge(input_data, cinfo->max_v_samp_factor,
160 cinfo->image_width, output_cols * h_expand);
163 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
164 outptr = output_data[outrow];
165 for (outcol = 0, outcol_h = 0; outcol < output_cols;
166 outcol++, outcol_h += h_expand) {
168 for (v = 0; v < v_expand; v++) {
169 inptr = input_data[inrow+v] + outcol_h;
170 for (h = 0; h < h_expand; h++) {
171 outvalue += (INT32) GETJSAMPLE(*inptr++);
174 *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
182 * Downsample pixel values of a single component.
183 * This version handles the special case of a full-size component,
188 fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
189 JSAMPARRAY input_data, JSAMPARRAY output_data)
192 jcopy_sample_rows(input_data, 0, output_data, 0,
193 cinfo->max_v_samp_factor, cinfo->image_width);
195 expand_right_edge(output_data, cinfo->max_v_samp_factor,
196 cinfo->image_width, compptr->width_in_data_units * cinfo->data_unit);
201 * Downsample pixel values of a single component.
202 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
205 * A note about the "bias" calculations: when rounding fractional values to
206 * integer, we do not want to always round 0.5 up to the next integer.
207 * If we did that, we'd introduce a noticeable bias towards larger values.
208 * Instead, this code is arranged so that 0.5 will be rounded up or down at
209 * alternate pixel locations (a simple ordered dither pattern).
213 h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
214 JSAMPARRAY input_data, JSAMPARRAY output_data)
218 JDIMENSION output_cols = compptr->width_in_data_units * cinfo->data_unit;
219 register JSAMPROW inptr, outptr;
222 /* Expand input data enough to let all the output samples be generated
223 * by the standard loop. Special-casing padded output would be more
226 expand_right_edge(input_data, cinfo->max_v_samp_factor,
227 cinfo->image_width, output_cols * 2);
229 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
230 outptr = output_data[outrow];
231 inptr = input_data[outrow];
232 bias = 0; /* bias = 0,1,0,1,... for successive samples */
233 for (outcol = 0; outcol < output_cols; outcol++) {
234 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
236 bias ^= 1; /* 0=>1, 1=>0 */
244 * Downsample pixel values of a single component.
245 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
250 h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
251 JSAMPARRAY input_data, JSAMPARRAY output_data)
255 JDIMENSION output_cols = compptr->width_in_data_units * cinfo->data_unit;
256 register JSAMPROW inptr0, inptr1, outptr;
259 /* Expand input data enough to let all the output samples be generated
260 * by the standard loop. Special-casing padded output would be more
263 expand_right_edge(input_data, cinfo->max_v_samp_factor,
264 cinfo->image_width, output_cols * 2);
267 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
268 outptr = output_data[outrow];
269 inptr0 = input_data[inrow];
270 inptr1 = input_data[inrow+1];
271 bias = 1; /* bias = 1,2,1,2,... for successive samples */
272 for (outcol = 0; outcol < output_cols; outcol++) {
273 *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
274 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
276 bias ^= 3; /* 1=>2, 2=>1 */
277 inptr0 += 2; inptr1 += 2;
284 #ifdef INPUT_SMOOTHING_SUPPORTED
287 * Downsample pixel values of a single component.
288 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
289 * with smoothing. One row of context is required.
293 h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
294 JSAMPARRAY input_data, JSAMPARRAY output_data)
298 JDIMENSION output_cols = compptr->width_in_data_units * cinfo->data_unit;
299 register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
300 INT32 membersum, neighsum, memberscale, neighscale;
302 /* Expand input data enough to let all the output samples be generated
303 * by the standard loop. Special-casing padded output would be more
306 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
307 cinfo->image_width, output_cols * 2);
309 /* We don't bother to form the individual "smoothed" input pixel values;
310 * we can directly compute the output which is the average of the four
311 * smoothed values. Each of the four member pixels contributes a fraction
312 * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
313 * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
314 * output. The four corner-adjacent neighbor pixels contribute a fraction
315 * SF to just one smoothed pixel, or SF/4 to the final output; while the
316 * eight edge-adjacent neighbors contribute SF to each of two smoothed
317 * pixels, or SF/2 overall. In order to use integer arithmetic, these
318 * factors are scaled by 2^16 = 65536.
319 * Also recall that SF = smoothing_factor / 1024.
322 memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
323 neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
326 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
327 outptr = output_data[outrow];
328 inptr0 = input_data[inrow];
329 inptr1 = input_data[inrow+1];
330 above_ptr = input_data[inrow-1];
331 below_ptr = input_data[inrow+2];
333 /* Special case for first column: pretend column -1 is same as column 0 */
334 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
335 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
336 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
337 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
338 GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
339 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
340 neighsum += neighsum;
341 neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
342 GETJSAMPLE(*below_ptr) + GETJSAMPLE(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;
347 for (colctr = output_cols - 2; colctr > 0; colctr--) {
348 /* sum of pixels directly mapped to this output element */
349 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
350 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
351 /* sum of edge-neighbor pixels */
352 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
353 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
354 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
355 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
356 /* The edge-neighbors count twice as much as corner-neighbors */
357 neighsum += neighsum;
358 /* Add in the corner-neighbors */
359 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
360 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
361 /* form final output scaled up by 2^16 */
362 membersum = membersum * memberscale + neighsum * neighscale;
363 /* round, descale and output it */
364 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
365 inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
368 /* Special case for last column */
369 membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
370 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
371 neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
372 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
373 GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
374 GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
375 neighsum += neighsum;
376 neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
377 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
378 membersum = membersum * memberscale + neighsum * neighscale;
379 *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
387 * Downsample pixel values of a single component.
388 * This version handles the special case of a full-size component,
389 * with smoothing. One row of context is required.
393 fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
394 JSAMPARRAY input_data, JSAMPARRAY output_data)
398 JDIMENSION output_cols = compptr->width_in_data_units * cinfo->data_unit;
399 register JSAMPROW inptr, above_ptr, below_ptr, outptr;
400 INT32 membersum, neighsum, memberscale, neighscale;
401 int colsum, lastcolsum, nextcolsum;
403 /* Expand input data enough to let all the output samples be generated
404 * by the standard loop. Special-casing padded output would be more
407 expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
408 cinfo->image_width, output_cols);
410 /* Each of the eight neighbor pixels contributes a fraction SF to the
411 * smoothed pixel, while the main pixel contributes (1-8*SF). In order
412 * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
413 * Also recall that SF = smoothing_factor / 1024.
416 memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
417 neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
419 for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
420 outptr = output_data[outrow];
421 inptr = input_data[outrow];
422 above_ptr = input_data[outrow-1];
423 below_ptr = input_data[outrow+1];
425 /* Special case for first column */
426 colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
428 membersum = GETJSAMPLE(*inptr++);
429 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
431 neighsum = colsum + (colsum - membersum) + nextcolsum;
432 membersum = membersum * memberscale + neighsum * neighscale;
433 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
434 lastcolsum = colsum; colsum = nextcolsum;
436 for (colctr = output_cols - 2; colctr > 0; colctr--) {
437 membersum = GETJSAMPLE(*inptr++);
438 above_ptr++; below_ptr++;
439 nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
441 neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
442 membersum = membersum * memberscale + neighsum * neighscale;
443 *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
444 lastcolsum = colsum; colsum = nextcolsum;
447 /* Special case for last column */
448 membersum = GETJSAMPLE(*inptr);
449 neighsum = lastcolsum + (colsum - membersum) + colsum;
450 membersum = membersum * memberscale + neighsum * neighscale;
451 *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
456 #endif /* INPUT_SMOOTHING_SUPPORTED */
460 * Module initialization routine for downsampling.
461 * Note that we must select a routine for each component.
465 jinit_downsampler (j_compress_ptr cinfo)
467 my_downsample_ptr downsample;
469 jpeg_component_info * compptr;
470 boolean smoothok = TRUE;
472 downsample = (my_downsample_ptr)
473 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
474 SIZEOF(my_downsampler));
475 cinfo->downsample = (struct jpeg_downsampler *) downsample;
476 downsample->pub.start_pass = start_pass_downsample;
477 downsample->pub.downsample = sep_downsample;
478 downsample->pub.need_context_rows = FALSE;
480 if (cinfo->CCIR601_sampling)
481 ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
483 /* Verify we can handle the sampling factors, and set up method pointers */
484 for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
486 if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
487 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
488 #ifdef INPUT_SMOOTHING_SUPPORTED
489 if (cinfo->smoothing_factor) {
490 downsample->methods[ci] = fullsize_smooth_downsample;
491 downsample->pub.need_context_rows = TRUE;
494 downsample->methods[ci] = fullsize_downsample;
495 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
496 compptr->v_samp_factor == cinfo->max_v_samp_factor) {
498 downsample->methods[ci] = h2v1_downsample;
499 } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
500 compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
501 #ifdef INPUT_SMOOTHING_SUPPORTED
502 if (cinfo->smoothing_factor) {
503 downsample->methods[ci] = h2v2_smooth_downsample;
504 downsample->pub.need_context_rows = TRUE;
507 downsample->methods[ci] = h2v2_downsample;
508 } else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
509 (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
511 downsample->methods[ci] = int_downsample;
513 ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
516 #ifdef INPUT_SMOOTHING_SUPPORTED
517 if (cinfo->smoothing_factor && !smoothok)
518 TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);