reactos/dll/3rdparty/libjpeg/jcsample.c

   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)
  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)
  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)
 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)
 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)
 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)
 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)
 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)
 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)
 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)
 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 }