4 * Copyright (C) 1991-1996, Thomas G. Lane.
5 * Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
6 * This file is part of the Independent JPEG Group's software.
7 * For conditions of distribution and use, see the accompanying README file.
9 * This file contains downsampling routines.
11 * Downsampling input data is counted in "row groups". A row group
12 * is defined to be max_v_samp_factor pixel rows of each component,
13 * from which the downsampler produces v_samp_factor sample rows.
14 * A single row group is processed in each call to the downsampler module.
16 * The downsampler is responsible for edge-expansion of its output data
17 * to fill an integral number of DCT blocks horizontally. The source buffer
18 * may be modified if it is helpful for this purpose (the source buffer is
19 * allocated wide enough to correspond to the desired output width).
20 * The caller (the prep controller) is responsible for vertical padding.
22 * The downsampler may request "context rows" by setting need_context_rows
23 * during startup. In this case, the input arrays will contain at least
24 * one row group's worth of pixels above and below the passed-in data;
25 * the caller will create dummy rows at image top and bottom by replicating
26 * the first or last real pixel row.
28 * An excellent reference for image resampling is
29 * Digital Image Warping, George Wolberg, 1990.
30 * Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
32 * The downsampling algorithm used here is a simple average of the source
33 * pixels covered by the output pixel. The hi-falutin sampling literature
34 * refers to this as a "box filter". In general the characteristics of a box
35 * filter are not very good, but for the specific cases we normally use (1:1
36 * and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
37 * nearly so bad. If you intend to use other sampling ratios, you'd be well
38 * advised to improve this code.
40 * A simple input-smoothing capability is provided. This is mainly intended
41 * for cleaning up color-dithered GIF input files (if you find it inadequate,
42 * we suggest using an external filtering program such as pnmconvol). When
43 * enabled, each input pixel P is replaced by a weighted sum of itself and its
44 * eight neighbors. P's weight is 1-8*SF and each neighbor's weight is SF,
45 * where SF = (smoothing_factor / 1024).
46 * Currently, smoothing is only supported for 2h2v sampling factors.
49 #define JPEG_INTERNALS
55 /* Pointer to routine to downsample a single component */
56 typedef JMETHOD(void, downsample1_ptr
,
57 (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
58 JSAMPARRAY input_data
, JSAMPARRAY output_data
));
60 /* Private subobject */
63 struct jpeg_downsampler pub
; /* public fields */
65 /* Downsampling method pointers, one per component */
66 downsample1_ptr methods
[MAX_COMPONENTS
];
69 typedef my_downsampler
* my_downsample_ptr
;
73 * Initialize for a downsampling pass.
77 start_pass_downsample (j_compress_ptr cinfo
)
84 * Expand a component horizontally from width input_cols to width output_cols,
85 * by duplicating the rightmost samples.
89 expand_right_edge (JSAMPARRAY image_data
, int num_rows
,
90 JDIMENSION input_cols
, JDIMENSION output_cols
)
92 register JSAMPROW ptr
;
93 register JSAMPLE pixval
;
96 int numcols
= (int) (output_cols
- input_cols
);
99 for (row
= 0; row
< num_rows
; row
++) {
100 ptr
= image_data
[row
] + input_cols
;
101 pixval
= ptr
[-1]; /* don't need GETJSAMPLE() here */
102 for (count
= numcols
; count
> 0; count
--)
110 * Do downsampling for a whole row group (all components).
112 * In this version we simply downsample each component independently.
116 sep_downsample (j_compress_ptr cinfo
,
117 JSAMPIMAGE input_buf
, JDIMENSION in_row_index
,
118 JSAMPIMAGE output_buf
, JDIMENSION out_row_group_index
)
120 my_downsample_ptr downsample
= (my_downsample_ptr
) cinfo
->downsample
;
122 jpeg_component_info
* compptr
;
123 JSAMPARRAY in_ptr
, out_ptr
;
125 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
127 in_ptr
= input_buf
[ci
] + in_row_index
;
128 out_ptr
= output_buf
[ci
] + (out_row_group_index
* compptr
->v_samp_factor
);
129 (*downsample
->methods
[ci
]) (cinfo
, compptr
, in_ptr
, out_ptr
);
135 * Downsample pixel values of a single component.
136 * One row group is processed per call.
137 * This version handles arbitrary integral sampling ratios, without smoothing.
138 * Note that this version is not actually used for customary sampling ratios.
142 int_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
143 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
145 int inrow
, outrow
, h_expand
, v_expand
, numpix
, numpix2
, h
, v
;
146 JDIMENSION outcol
, outcol_h
; /* outcol_h == outcol*h_expand */
147 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
148 JSAMPROW inptr
, outptr
;
151 h_expand
= cinfo
->max_h_samp_factor
/ compptr
->h_samp_factor
;
152 v_expand
= cinfo
->max_v_samp_factor
/ compptr
->v_samp_factor
;
153 numpix
= h_expand
* v_expand
;
156 /* Expand input data enough to let all the output samples be generated
157 * by the standard loop. Special-casing padded output would be more
160 expand_right_edge(input_data
, cinfo
->max_v_samp_factor
,
161 cinfo
->image_width
, output_cols
* h_expand
);
164 for (outrow
= 0; outrow
< compptr
->v_samp_factor
; outrow
++) {
165 outptr
= output_data
[outrow
];
166 for (outcol
= 0, outcol_h
= 0; outcol
< output_cols
;
167 outcol
++, outcol_h
+= h_expand
) {
169 for (v
= 0; v
< v_expand
; v
++) {
170 inptr
= input_data
[inrow
+v
] + outcol_h
;
171 for (h
= 0; h
< h_expand
; h
++) {
172 outvalue
+= (INT32
) GETJSAMPLE(*inptr
++);
175 *outptr
++ = (JSAMPLE
) ((outvalue
+ numpix2
) / numpix
);
183 * Downsample pixel values of a single component.
184 * This version handles the special case of a full-size component,
189 fullsize_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
190 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
193 jcopy_sample_rows(input_data
, 0, output_data
, 0,
194 cinfo
->max_v_samp_factor
, cinfo
->image_width
);
196 expand_right_edge(output_data
, cinfo
->max_v_samp_factor
,
197 cinfo
->image_width
, compptr
->width_in_blocks
* DCTSIZE
);
202 * Downsample pixel values of a single component.
203 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
206 * A note about the "bias" calculations: when rounding fractional values to
207 * integer, we do not want to always round 0.5 up to the next integer.
208 * If we did that, we'd introduce a noticeable bias towards larger values.
209 * Instead, this code is arranged so that 0.5 will be rounded up or down at
210 * alternate pixel locations (a simple ordered dither pattern).
214 h2v1_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
215 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
219 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
220 register JSAMPROW inptr
, outptr
;
223 /* Expand input data enough to let all the output samples be generated
224 * by the standard loop. Special-casing padded output would be more
227 expand_right_edge(input_data
, cinfo
->max_v_samp_factor
,
228 cinfo
->image_width
, output_cols
* 2);
230 for (outrow
= 0; outrow
< compptr
->v_samp_factor
; outrow
++) {
231 outptr
= output_data
[outrow
];
232 inptr
= input_data
[outrow
];
233 bias
= 0; /* bias = 0,1,0,1,... for successive samples */
234 for (outcol
= 0; outcol
< output_cols
; outcol
++) {
235 *outptr
++ = (JSAMPLE
) ((GETJSAMPLE(*inptr
) + GETJSAMPLE(inptr
[1])
237 bias
^= 1; /* 0=>1, 1=>0 */
245 * Downsample pixel values of a single component.
246 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
251 h2v2_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
252 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
256 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
257 register JSAMPROW inptr0
, inptr1
, outptr
;
260 /* Expand input data enough to let all the output samples be generated
261 * by the standard loop. Special-casing padded output would be more
264 expand_right_edge(input_data
, cinfo
->max_v_samp_factor
,
265 cinfo
->image_width
, output_cols
* 2);
268 for (outrow
= 0; outrow
< compptr
->v_samp_factor
; outrow
++) {
269 outptr
= output_data
[outrow
];
270 inptr0
= input_data
[inrow
];
271 inptr1
= input_data
[inrow
+1];
272 bias
= 1; /* bias = 1,2,1,2,... for successive samples */
273 for (outcol
= 0; outcol
< output_cols
; outcol
++) {
274 *outptr
++ = (JSAMPLE
) ((GETJSAMPLE(*inptr0
) + GETJSAMPLE(inptr0
[1]) +
275 GETJSAMPLE(*inptr1
) + GETJSAMPLE(inptr1
[1])
277 bias
^= 3; /* 1=>2, 2=>1 */
278 inptr0
+= 2; inptr1
+= 2;
285 #ifdef INPUT_SMOOTHING_SUPPORTED
288 * Downsample pixel values of a single component.
289 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
290 * with smoothing. One row of context is required.
294 h2v2_smooth_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
295 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
299 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
300 register JSAMPROW inptr0
, inptr1
, above_ptr
, below_ptr
, outptr
;
301 INT32 membersum
, neighsum
, memberscale
, neighscale
;
303 /* Expand input data enough to let all the output samples be generated
304 * by the standard loop. Special-casing padded output would be more
307 expand_right_edge(input_data
- 1, cinfo
->max_v_samp_factor
+ 2,
308 cinfo
->image_width
, output_cols
* 2);
310 /* We don't bother to form the individual "smoothed" input pixel values;
311 * we can directly compute the output which is the average of the four
312 * smoothed values. Each of the four member pixels contributes a fraction
313 * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
314 * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
315 * output. The four corner-adjacent neighbor pixels contribute a fraction
316 * SF to just one smoothed pixel, or SF/4 to the final output; while the
317 * eight edge-adjacent neighbors contribute SF to each of two smoothed
318 * pixels, or SF/2 overall. In order to use integer arithmetic, these
319 * factors are scaled by 2^16 = 65536.
320 * Also recall that SF = smoothing_factor / 1024.
323 memberscale
= 16384 - cinfo
->smoothing_factor
* 80; /* scaled (1-5*SF)/4 */
324 neighscale
= cinfo
->smoothing_factor
* 16; /* scaled SF/4 */
327 for (outrow
= 0; outrow
< compptr
->v_samp_factor
; outrow
++) {
328 outptr
= output_data
[outrow
];
329 inptr0
= input_data
[inrow
];
330 inptr1
= input_data
[inrow
+1];
331 above_ptr
= input_data
[inrow
-1];
332 below_ptr
= input_data
[inrow
+2];
334 /* Special case for first column: pretend column -1 is same as column 0 */
335 membersum
= GETJSAMPLE(*inptr0
) + GETJSAMPLE(inptr0
[1]) +
336 GETJSAMPLE(*inptr1
) + GETJSAMPLE(inptr1
[1]);
337 neighsum
= GETJSAMPLE(*above_ptr
) + GETJSAMPLE(above_ptr
[1]) +
338 GETJSAMPLE(*below_ptr
) + GETJSAMPLE(below_ptr
[1]) +
339 GETJSAMPLE(*inptr0
) + GETJSAMPLE(inptr0
[2]) +
340 GETJSAMPLE(*inptr1
) + GETJSAMPLE(inptr1
[2]);
341 neighsum
+= neighsum
;
342 neighsum
+= GETJSAMPLE(*above_ptr
) + GETJSAMPLE(above_ptr
[2]) +
343 GETJSAMPLE(*below_ptr
) + GETJSAMPLE(below_ptr
[2]);
344 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
345 *outptr
++ = (JSAMPLE
) ((membersum
+ 32768) >> 16);
346 inptr0
+= 2; inptr1
+= 2; above_ptr
+= 2; below_ptr
+= 2;
348 for (colctr
= output_cols
- 2; colctr
> 0; colctr
--) {
349 /* sum of pixels directly mapped to this output element */
350 membersum
= GETJSAMPLE(*inptr0
) + GETJSAMPLE(inptr0
[1]) +
351 GETJSAMPLE(*inptr1
) + GETJSAMPLE(inptr1
[1]);
352 /* sum of edge-neighbor pixels */
353 neighsum
= GETJSAMPLE(*above_ptr
) + GETJSAMPLE(above_ptr
[1]) +
354 GETJSAMPLE(*below_ptr
) + GETJSAMPLE(below_ptr
[1]) +
355 GETJSAMPLE(inptr0
[-1]) + GETJSAMPLE(inptr0
[2]) +
356 GETJSAMPLE(inptr1
[-1]) + GETJSAMPLE(inptr1
[2]);
357 /* The edge-neighbors count twice as much as corner-neighbors */
358 neighsum
+= neighsum
;
359 /* Add in the corner-neighbors */
360 neighsum
+= GETJSAMPLE(above_ptr
[-1]) + GETJSAMPLE(above_ptr
[2]) +
361 GETJSAMPLE(below_ptr
[-1]) + GETJSAMPLE(below_ptr
[2]);
362 /* form final output scaled up by 2^16 */
363 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
364 /* round, descale and output it */
365 *outptr
++ = (JSAMPLE
) ((membersum
+ 32768) >> 16);
366 inptr0
+= 2; inptr1
+= 2; above_ptr
+= 2; below_ptr
+= 2;
369 /* Special case for last column */
370 membersum
= GETJSAMPLE(*inptr0
) + GETJSAMPLE(inptr0
[1]) +
371 GETJSAMPLE(*inptr1
) + GETJSAMPLE(inptr1
[1]);
372 neighsum
= GETJSAMPLE(*above_ptr
) + GETJSAMPLE(above_ptr
[1]) +
373 GETJSAMPLE(*below_ptr
) + GETJSAMPLE(below_ptr
[1]) +
374 GETJSAMPLE(inptr0
[-1]) + GETJSAMPLE(inptr0
[1]) +
375 GETJSAMPLE(inptr1
[-1]) + GETJSAMPLE(inptr1
[1]);
376 neighsum
+= neighsum
;
377 neighsum
+= GETJSAMPLE(above_ptr
[-1]) + GETJSAMPLE(above_ptr
[1]) +
378 GETJSAMPLE(below_ptr
[-1]) + GETJSAMPLE(below_ptr
[1]);
379 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
380 *outptr
= (JSAMPLE
) ((membersum
+ 32768) >> 16);
388 * Downsample pixel values of a single component.
389 * This version handles the special case of a full-size component,
390 * with smoothing. One row of context is required.
394 fullsize_smooth_downsample (j_compress_ptr cinfo
, jpeg_component_info
*compptr
,
395 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
399 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
400 register JSAMPROW inptr
, above_ptr
, below_ptr
, outptr
;
401 INT32 membersum
, neighsum
, memberscale
, neighscale
;
402 int colsum
, lastcolsum
, nextcolsum
;
404 /* Expand input data enough to let all the output samples be generated
405 * by the standard loop. Special-casing padded output would be more
408 expand_right_edge(input_data
- 1, cinfo
->max_v_samp_factor
+ 2,
409 cinfo
->image_width
, output_cols
);
411 /* Each of the eight neighbor pixels contributes a fraction SF to the
412 * smoothed pixel, while the main pixel contributes (1-8*SF). In order
413 * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
414 * Also recall that SF = smoothing_factor / 1024.
417 memberscale
= 65536L - cinfo
->smoothing_factor
* 512L; /* scaled 1-8*SF */
418 neighscale
= cinfo
->smoothing_factor
* 64; /* scaled SF */
420 for (outrow
= 0; outrow
< compptr
->v_samp_factor
; outrow
++) {
421 outptr
= output_data
[outrow
];
422 inptr
= input_data
[outrow
];
423 above_ptr
= input_data
[outrow
-1];
424 below_ptr
= input_data
[outrow
+1];
426 /* Special case for first column */
427 colsum
= GETJSAMPLE(*above_ptr
++) + GETJSAMPLE(*below_ptr
++) +
429 membersum
= GETJSAMPLE(*inptr
++);
430 nextcolsum
= GETJSAMPLE(*above_ptr
) + GETJSAMPLE(*below_ptr
) +
432 neighsum
= colsum
+ (colsum
- membersum
) + nextcolsum
;
433 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
434 *outptr
++ = (JSAMPLE
) ((membersum
+ 32768) >> 16);
435 lastcolsum
= colsum
; colsum
= nextcolsum
;
437 for (colctr
= output_cols
- 2; colctr
> 0; colctr
--) {
438 membersum
= GETJSAMPLE(*inptr
++);
439 above_ptr
++; below_ptr
++;
440 nextcolsum
= GETJSAMPLE(*above_ptr
) + GETJSAMPLE(*below_ptr
) +
442 neighsum
= lastcolsum
+ (colsum
- membersum
) + nextcolsum
;
443 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
444 *outptr
++ = (JSAMPLE
) ((membersum
+ 32768) >> 16);
445 lastcolsum
= colsum
; colsum
= nextcolsum
;
448 /* Special case for last column */
449 membersum
= GETJSAMPLE(*inptr
);
450 neighsum
= lastcolsum
+ (colsum
- membersum
) + colsum
;
451 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
452 *outptr
= (JSAMPLE
) ((membersum
+ 32768) >> 16);
457 #endif /* INPUT_SMOOTHING_SUPPORTED */
461 * Module initialization routine for downsampling.
462 * Note that we must select a routine for each component.
466 jinit_downsampler (j_compress_ptr cinfo
)
468 my_downsample_ptr downsample
;
470 jpeg_component_info
* compptr
;
471 boolean smoothok
= TRUE
;
473 downsample
= (my_downsample_ptr
)
474 (*cinfo
->mem
->alloc_small
) ((j_common_ptr
) cinfo
, JPOOL_IMAGE
,
475 SIZEOF(my_downsampler
));
476 cinfo
->downsample
= (struct jpeg_downsampler
*) downsample
;
477 downsample
->pub
.start_pass
= start_pass_downsample
;
478 downsample
->pub
.downsample
= sep_downsample
;
479 downsample
->pub
.need_context_rows
= FALSE
;
481 if (cinfo
->CCIR601_sampling
)
482 ERREXIT(cinfo
, JERR_CCIR601_NOTIMPL
);
484 /* Verify we can handle the sampling factors, and set up method pointers */
485 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
487 if (compptr
->h_samp_factor
== cinfo
->max_h_samp_factor
&&
488 compptr
->v_samp_factor
== cinfo
->max_v_samp_factor
) {
489 #ifdef INPUT_SMOOTHING_SUPPORTED
490 if (cinfo
->smoothing_factor
) {
491 downsample
->methods
[ci
] = fullsize_smooth_downsample
;
492 downsample
->pub
.need_context_rows
= TRUE
;
495 downsample
->methods
[ci
] = fullsize_downsample
;
496 } else if (compptr
->h_samp_factor
* 2 == cinfo
->max_h_samp_factor
&&
497 compptr
->v_samp_factor
== cinfo
->max_v_samp_factor
) {
499 if (jsimd_can_h2v1_downsample())
500 downsample
->methods
[ci
] = jsimd_h2v1_downsample
;
502 downsample
->methods
[ci
] = h2v1_downsample
;
503 } else if (compptr
->h_samp_factor
* 2 == cinfo
->max_h_samp_factor
&&
504 compptr
->v_samp_factor
* 2 == cinfo
->max_v_samp_factor
) {
505 #ifdef INPUT_SMOOTHING_SUPPORTED
506 if (cinfo
->smoothing_factor
) {
507 downsample
->methods
[ci
] = h2v2_smooth_downsample
;
508 downsample
->pub
.need_context_rows
= TRUE
;
511 if (jsimd_can_h2v2_downsample())
512 downsample
->methods
[ci
] = jsimd_h2v2_downsample
;
514 downsample
->methods
[ci
] = h2v2_downsample
;
515 } else if ((cinfo
->max_h_samp_factor
% compptr
->h_samp_factor
) == 0 &&
516 (cinfo
->max_v_samp_factor
% compptr
->v_samp_factor
) == 0) {
518 downsample
->methods
[ci
] = int_downsample
;
520 ERREXIT(cinfo
, JERR_FRACT_SAMPLE_NOTIMPL
);
523 #ifdef INPUT_SMOOTHING_SUPPORTED
524 if (cinfo
->smoothing_factor
&& !smoothok
)
525 TRACEMS(cinfo
, 0, JTRC_SMOOTH_NOTIMPL
);