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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
 *
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 * Downsampling input data is counted in "row groups".  A row group
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 * is defined to be max_v_samp_factor pixel rows of each component,
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 * from which the downsampler produces v_samp_factor sample rows.
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 * A single row group is processed in each call to the downsampler module.
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 *
15
 * The downsampler is responsible for edge-expansion of its output data
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 * to fill an integral number of DCT blocks horizontally.  The source buffer
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 * may be modified if it is helpful for this purpose (the source buffer is
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 * allocated wide enough to correspond to the desired output width).
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 * The caller (the prep controller) is responsible for vertical padding.
20
 *
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 * 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;
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 * 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
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 *   Digital Image Warping, George Wolberg, 1990.
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 *   Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
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 *
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
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 * filter are not very good, but for the specific cases we normally use (1:1
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 * 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
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 * enabled, each input pixel P is replaced by a weighted sum of itself and its
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 * 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,
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		(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
} my_downsampler;
66

67
typedef my_downsampler * my_downsample_ptr;
68

69

70
/*
71
 * Initialize for a downsampling pass.
72
 */
73

74
METHODDEF(void)
75
start_pass_downsample (j_compress_ptr cinfo)
76
{
77
  /* no work for now */
78
}
79

80

81
/*
82
 * Expand a component horizontally from width input_cols to width output_cols,
83
 * by duplicating the rightmost samples.
84
 */
85

86
LOCAL(void)
87
expand_right_edge (JSAMPARRAY image_data, int num_rows,
88
		   JDIMENSION input_cols, JDIMENSION output_cols)
89
{
90
  register JSAMPROW ptr;
91
  register JSAMPLE pixval;
92
  register int count;
93
  int row;
94
  int numcols = (int) (output_cols - input_cols);
95

96
  if (numcols > 0) {
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--)
101
	*ptr++ = pixval;
102
    }
103
  }
104
}
105

106

107
/*
108
 * Do downsampling for a whole row group (all components).
109
 *
110
 * In this version we simply downsample each component independently.
111
 */
112

113
METHODDEF(void)
114
sep_downsample (j_compress_ptr cinfo,
115
		JSAMPIMAGE input_buf, JDIMENSION in_row_index,
116
		JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
117
{
118
  my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
119
  int ci;
120
  jpeg_component_info * compptr;
121
  JSAMPARRAY in_ptr, out_ptr;
122

123
  for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
124
       ci++, compptr++) {
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);
128
  }
129
}
130

131

132
/*
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.
137
 */
138

139
METHODDEF(void)
140
int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
141
		JSAMPARRAY input_data, JSAMPARRAY output_data)
142
{
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;
147
  INT32 outvalue;
148

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;
152
  numpix2 = numpix/2;
153

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
156
   * efficient.
157
   */
158
  expand_right_edge(input_data, cinfo->max_v_samp_factor,
159
		    cinfo->image_width, output_cols * h_expand);
160

161
  inrow = 0;
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) {
166
      outvalue = 0;
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 += (INT32) GETJSAMPLE(*inptr++);
171
	}
172
      }
173
      *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
174
    }
175
    inrow += v_expand;
176
  }
177
}
178

179

180
/*
181
 * Downsample pixel values of a single component.
182
 * This version handles the special case of a full-size component,
183
 * without smoothing.
184
 */
185

186
METHODDEF(void)
187
fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
188
		     JSAMPARRAY input_data, JSAMPARRAY output_data)
189
{
190
  /* Copy the data */
191
  jcopy_sample_rows(input_data, 0, output_data, 0,
192
		    cinfo->max_v_samp_factor, cinfo->image_width);
193
  /* Edge-expand */
194
  expand_right_edge(output_data, cinfo->max_v_samp_factor,
195
		    cinfo->image_width, compptr->width_in_blocks * DCTSIZE);
196
}
197

198

199
/*
200
 * Downsample pixel values of a single component.
201
 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
202
 * without smoothing.
203
 *
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).
209
 */
210

211
METHODDEF(void)
212
h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
213
		 JSAMPARRAY input_data, JSAMPARRAY output_data)
214
{
215
  int outrow;
216
  JDIMENSION outcol;
217
  JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
218
  register JSAMPROW inptr, outptr;
219
  register int bias;
220

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
223
   * efficient.
224
   */
225
  expand_right_edge(input_data, cinfo->max_v_samp_factor,
226
		    cinfo->image_width, output_cols * 2);
227

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])
234
			      + bias) >> 1);
235
      bias ^= 1;		/* 0=>1, 1=>0 */
236
      inptr += 2;
237
    }
238
  }
239
}
240

241

242
/*
243
 * Downsample pixel values of a single component.
244
 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
245
 * without smoothing.
246
 */
247

248
METHODDEF(void)
249
h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
250
		 JSAMPARRAY input_data, JSAMPARRAY output_data)
251
{
252
  int inrow, outrow;
253
  JDIMENSION outcol;
254
  JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
255
  register JSAMPROW inptr0, inptr1, outptr;
256
  register int bias;
257

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
260
   * efficient.
261
   */
262
  expand_right_edge(input_data, cinfo->max_v_samp_factor,
263
		    cinfo->image_width, output_cols * 2);
264

265
  inrow = 0;
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])
274
			      + bias) >> 2);
275
      bias ^= 3;		/* 1=>2, 2=>1 */
276
      inptr0 += 2; inptr1 += 2;
277
    }
278
    inrow += 2;
279
  }
280
}
281

282

283
#ifdef INPUT_SMOOTHING_SUPPORTED
284

285
/*
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.
289
 */
290

291
METHODDEF(void)
292
h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
293
			JSAMPARRAY input_data, JSAMPARRAY output_data)
294
{
295
  int inrow, outrow;
296
  JDIMENSION colctr;
297
  JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
298
  register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
299
  INT32 membersum, neighsum, memberscale, neighscale;
300

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
303
   * efficient.
304
   */
305
  expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
306
		    cinfo->image_width, output_cols * 2);
307

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.
319
   */
320

321
  memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
322
  neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
323

324
  inrow = 0;
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];
331

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;
345

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;
365
    }
366

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);
379

380
    inrow += 2;
381
  }
382
}
383

384

385
/*
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.
389
 */
390

391
METHODDEF(void)
392
fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
393
			    JSAMPARRAY input_data, JSAMPARRAY output_data)
394
{
395
  int outrow;
396
  JDIMENSION colctr;
397
  JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
398
  register JSAMPROW inptr, above_ptr, below_ptr, outptr;
399
  INT32 membersum, neighsum, memberscale, neighscale;
400
  int colsum, lastcolsum, nextcolsum;
401

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
404
   * efficient.
405
   */
406
  expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
407
		    cinfo->image_width, output_cols);
408

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.
413
   */
414

415
  memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
416
  neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
417

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];
423

424
    /* Special case for first column */
425
    colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
426
	     GETJSAMPLE(*inptr);
427
    membersum = GETJSAMPLE(*inptr++);
428
    nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
429
		 GETJSAMPLE(*inptr);
430
    neighsum = colsum + (colsum - membersum) + nextcolsum;
431
    membersum = membersum * memberscale + neighsum * neighscale;
432
    *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
433
    lastcolsum = colsum; colsum = nextcolsum;
434

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) +
439
		   GETJSAMPLE(*inptr);
440
      neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
441
      membersum = membersum * memberscale + neighsum * neighscale;
442
      *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
443
      lastcolsum = colsum; colsum = nextcolsum;
444
    }
445

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);
451

452
  }
453
}
454

455
#endif /* INPUT_SMOOTHING_SUPPORTED */
456

457

458
/*
459
 * Module initialization routine for downsampling.
460
 * Note that we must select a routine for each component.
461
 */
462

463
GLOBAL(void)
464
jinit_downsampler (j_compress_ptr cinfo)
465
{
466
  my_downsample_ptr downsample;
467
  int ci;
468
  jpeg_component_info * compptr;
469
  boolean smoothok = TRUE;
470

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;
478

479
  if (cinfo->CCIR601_sampling)
480
    ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
481

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;
484
       ci++, compptr++) {
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;
491
      } else
492
#endif
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) {
496
      smoothok = FALSE;
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;
504
      } else
505
#endif
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) {
509
      smoothok = FALSE;
510
      downsample->methods[ci] = int_downsample;
511
    } else
512
      ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
513
  }
514

515
#ifdef INPUT_SMOOTHING_SUPPORTED
516
  if (cinfo->smoothing_factor && !smoothok)
517
    TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
518
#endif
519
}
520

521