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.
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
)
82 * Expand a component horizontally from width input_cols to width output_cols,
83 * by duplicating the rightmost samples.
87 expand_right_edge (JSAMPARRAY image_data
, int num_rows
,
88 JDIMENSION input_cols
, JDIMENSION output_cols
)
90 register JSAMPROW ptr
;
91 register JSAMPLE pixval
;
94 int numcols
= (int) (output_cols
- input_cols
);
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
--)
108 * Do downsampling for a whole row group (all components).
110 * In this version we simply downsample each component independently.
114 sep_downsample (j_compress_ptr cinfo
,
115 JSAMPIMAGE input_buf
, JDIMENSION in_row_index
,
116 JSAMPIMAGE output_buf
, JDIMENSION out_row_group_index
)
118 my_downsample_ptr downsample
= (my_downsample_ptr
) cinfo
->downsample
;
120 jpeg_component_info
* compptr
;
121 JSAMPARRAY in_ptr
, out_ptr
;
123 for (ci
= 0, compptr
= cinfo
->comp_info
; ci
< cinfo
->num_components
;
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
);
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.
140 int_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
141 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
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
;
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
;
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
158 expand_right_edge(input_data
, cinfo
->max_v_samp_factor
,
159 cinfo
->image_width
, output_cols
* h_expand
);
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
) {
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
+= (JPEG_INT32
) GETJSAMPLE(*inptr
++);
173 *outptr
++ = (JSAMPLE
) ((outvalue
+ numpix2
) / numpix
);
181 * Downsample pixel values of a single component.
182 * This version handles the special case of a full-size component,
187 fullsize_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
188 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
191 jcopy_sample_rows(input_data
, 0, output_data
, 0,
192 cinfo
->max_v_samp_factor
, cinfo
->image_width
);
194 expand_right_edge(output_data
, cinfo
->max_v_samp_factor
,
195 cinfo
->image_width
, compptr
->width_in_blocks
* DCTSIZE
);
200 * Downsample pixel values of a single component.
201 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
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).
212 h2v1_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
213 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
217 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
218 register JSAMPROW inptr
, outptr
;
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
225 expand_right_edge(input_data
, cinfo
->max_v_samp_factor
,
226 cinfo
->image_width
, output_cols
* 2);
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])
235 bias
^= 1; /* 0=>1, 1=>0 */
243 * Downsample pixel values of a single component.
244 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
249 h2v2_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
250 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
254 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
255 register JSAMPROW inptr0
, inptr1
, outptr
;
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
262 expand_right_edge(input_data
, cinfo
->max_v_samp_factor
,
263 cinfo
->image_width
, output_cols
* 2);
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])
275 bias
^= 3; /* 1=>2, 2=>1 */
276 inptr0
+= 2; inptr1
+= 2;
283 #ifdef INPUT_SMOOTHING_SUPPORTED
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.
292 h2v2_smooth_downsample (j_compress_ptr cinfo
, jpeg_component_info
* compptr
,
293 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
297 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
298 register JSAMPROW inptr0
, inptr1
, above_ptr
, below_ptr
, outptr
;
299 JPEG_INT32 membersum
, neighsum
, memberscale
, neighscale
;
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
305 expand_right_edge(input_data
- 1, cinfo
->max_v_samp_factor
+ 2,
306 cinfo
->image_width
, output_cols
* 2);
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.
321 memberscale
= 16384 - cinfo
->smoothing_factor
* 80; /* scaled (1-5*SF)/4 */
322 neighscale
= cinfo
->smoothing_factor
* 16; /* scaled SF/4 */
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];
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;
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;
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);
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.
392 fullsize_smooth_downsample (j_compress_ptr cinfo
, jpeg_component_info
*compptr
,
393 JSAMPARRAY input_data
, JSAMPARRAY output_data
)
397 JDIMENSION output_cols
= compptr
->width_in_blocks
* DCTSIZE
;
398 register JSAMPROW inptr
, above_ptr
, below_ptr
, outptr
;
399 JPEG_INT32 membersum
, neighsum
, memberscale
, neighscale
;
400 int colsum
, lastcolsum
, nextcolsum
;
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
406 expand_right_edge(input_data
- 1, cinfo
->max_v_samp_factor
+ 2,
407 cinfo
->image_width
, output_cols
);
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.
415 memberscale
= 65536L - cinfo
->smoothing_factor
* 512L; /* scaled 1-8*SF */
416 neighscale
= cinfo
->smoothing_factor
* 64; /* scaled SF */
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];
424 /* Special case for first column */
425 colsum
= GETJSAMPLE(*above_ptr
++) + GETJSAMPLE(*below_ptr
++) +
427 membersum
= GETJSAMPLE(*inptr
++);
428 nextcolsum
= GETJSAMPLE(*above_ptr
) + GETJSAMPLE(*below_ptr
) +
430 neighsum
= colsum
+ (colsum
- membersum
) + nextcolsum
;
431 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
432 *outptr
++ = (JSAMPLE
) ((membersum
+ 32768) >> 16);
433 lastcolsum
= colsum
; colsum
= nextcolsum
;
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
) +
440 neighsum
= lastcolsum
+ (colsum
- membersum
) + nextcolsum
;
441 membersum
= membersum
* memberscale
+ neighsum
* neighscale
;
442 *outptr
++ = (JSAMPLE
) ((membersum
+ 32768) >> 16);
443 lastcolsum
= colsum
; colsum
= nextcolsum
;
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);
455 #endif /* INPUT_SMOOTHING_SUPPORTED */
459 * Module initialization routine for downsampling.
460 * Note that we must select a routine for each component.
464 jinit_downsampler (j_compress_ptr cinfo
)
466 my_downsample_ptr downsample
;
468 jpeg_component_info
* compptr
;
469 boolean smoothok
= TRUE
;
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
;
479 if (cinfo
->CCIR601_sampling
)
480 ERREXIT(cinfo
, JERR_CCIR601_NOTIMPL
);
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
;
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
;
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
) {
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
;
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) {
510 downsample
->methods
[ci
] = int_downsample
;
512 ERREXIT(cinfo
, JERR_FRACT_SAMPLE_NOTIMPL
);
515 #ifdef INPUT_SMOOTHING_SUPPORTED
516 if (cinfo
->smoothing_factor
&& !smoothok
)
517 TRACEMS(cinfo
, 0, JTRC_SMOOTH_NOTIMPL
);