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)
start_pass_downsample(j_compress_ptr cinfo)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)
expand_right_edge(JSAMPARRAY image_data,int num_rows,JDIMENSION input_cols,JDIMENSION output_cols)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)
sep_downsample(j_compress_ptr cinfo,JSAMPIMAGE input_buf,JDIMENSION in_row_index,JSAMPIMAGE output_buf,JDIMENSION out_row_group_index)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)
int_downsample(j_compress_ptr cinfo,jpeg_component_info * compptr,JSAMPARRAY input_data,JSAMPARRAY output_data)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)
fullsize_downsample(j_compress_ptr cinfo,jpeg_component_info * compptr,JSAMPARRAY input_data,JSAMPARRAY output_data)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)
h2v1_downsample(j_compress_ptr cinfo,jpeg_component_info * compptr,JSAMPARRAY input_data,JSAMPARRAY output_data)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)
h2v2_downsample(j_compress_ptr cinfo,jpeg_component_info * compptr,JSAMPARRAY input_data,JSAMPARRAY output_data)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)
h2v2_smooth_downsample(j_compress_ptr cinfo,jpeg_component_info * compptr,JSAMPARRAY input_data,JSAMPARRAY output_data)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)
fullsize_smooth_downsample(j_compress_ptr cinfo,jpeg_component_info * compptr,JSAMPARRAY input_data,JSAMPARRAY output_data)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)
jinit_downsampler(j_compress_ptr cinfo)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 }
546