libs/jpeg/jcsample.c

   1 /*
   2  * jcsample.c
   3  *
   4  * Copyright (C) 1991-1996, Thomas G. Lane.
   5  * Modified 2003-2020 by Guido Vollbeding.
   6  * This file is part of the Independent JPEG Group's software.
   7  * For conditions of distribution and use, see the accompanying README file.
   8  *
   9  * This file contains downsampling routines.
  10  *
  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.
  15  *
  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.
  21  *
  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.
  27  *
  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.
  31  *
  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.
  39  *
  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.
  47  */
  48
  49 #define JPEG_INTERNALS
  50 #include "jinclude.h"
  51 #include "jpeglib.h"
  52
  53
  54 /* Pointer to routine to downsample a single component */
  55 typedef JMETHOD(void, downsample1_ptr,
  56                 (j_compress_ptr cinfo, jpeg_component_info * compptr,
  57                  JSAMPARRAY input_data, JSAMPARRAY output_data));
  58
  59 /* Private subobject */
  60
  61 typedef struct {
  62   struct jpeg_downsampler pub;  /* public fields */
  63
  64   /* Downsampling method pointers, one per component */
  65   downsample1_ptr methods[MAX_COMPONENTS];
  66
  67   /* Height of an output row group for each component. */
  68   int rowgroup_height[MAX_COMPONENTS];
  69
  70   /* These arrays save pixel expansion factors so that int_downsample need not
  71    * recompute them each time.  They are unused for other downsampling methods.
  72    */
  73   UINT8 h_expand[MAX_COMPONENTS];
  74   UINT8 v_expand[MAX_COMPONENTS];
  75 } my_downsampler;
  76
  77 typedef my_downsampler * my_downsample_ptr;
  78
  79
  80 /*
  81  * Initialize for a downsampling pass.
  82  */
  83
  84 METHODDEF(void)
  85 start_pass_downsample (j_compress_ptr cinfo)
  86 {
  87   /* no work for now */
  88 }
  89
  90
  91 /*
  92  * Expand a component horizontally from width input_cols to width output_cols,
  93  * by duplicating the rightmost samples.
  94  */
  95
  96 LOCAL(void)
  97 expand_right_edge (JSAMPARRAY image_data, int num_rows,
  98                    JDIMENSION input_cols, JDIMENSION output_cols)
  99 {
 100   register JSAMPROW ptr;
 101   register JSAMPLE pixval;
 102   register int count;
 103   int row;
 104   int numcols = (int) (output_cols - input_cols);
 105
 106   if (numcols > 0) {
 107     for (row = 0; row < num_rows; row++) {
 108       ptr = image_data[row] + input_cols;
 109       pixval = ptr[-1];         /* don't need GETJSAMPLE() here */
 110       for (count = numcols; count > 0; count--)
 111         *ptr++ = pixval;
 112     }
 113   }
 114 }
 115
 116
 117 /*
 118  * Do downsampling for a whole row group (all components).
 119  *
 120  * In this version we simply downsample each component independently.
 121  */
 122
 123 METHODDEF(void)
 124 sep_downsample (j_compress_ptr cinfo,
 125                 JSAMPIMAGE input_buf, JDIMENSION in_row_index,
 126                 JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
 127 {
 128   my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
 129   int ci;
 130   jpeg_component_info * compptr;
 131   JSAMPARRAY in_ptr, out_ptr;
 132
 133   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 134        ci++, compptr++) {
 135     in_ptr = input_buf[ci] + in_row_index;
 136     out_ptr = output_buf[ci] +
 137               (out_row_group_index * downsample->rowgroup_height[ci]);
 138     (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
 139   }
 140 }
 141
 142
 143 /*
 144  * Downsample pixel values of a single component.
 145  * One row group is processed per call.
 146  * This version handles arbitrary integral sampling ratios, without smoothing.
 147  * Note that this version is not actually used for customary sampling ratios.
 148  */
 149
 150 METHODDEF(void)
 151 int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 152                 JSAMPARRAY input_data, JSAMPARRAY output_data)
 153 {
 154   my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
 155   int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
 156   JDIMENSION outcol, outcol_h;  /* outcol_h == outcol*h_expand */
 157   JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
 158   JSAMPROW inptr, outptr;
 159   INT32 outvalue;
 160
 161   h_expand = downsample->h_expand[compptr->component_index];
 162   v_expand = downsample->v_expand[compptr->component_index];
 163   numpix = h_expand * v_expand;
 164   numpix2 = numpix/2;
 165
 166   /* Expand input data enough to let all the output samples be generated
 167    * by the standard loop.  Special-casing padded output would be more
 168    * efficient.
 169    */
 170   expand_right_edge(input_data, cinfo->max_v_samp_factor,
 171                     cinfo->image_width, output_cols * h_expand);
 172
 173   inrow = outrow = 0;
 174   while (inrow < cinfo->max_v_samp_factor) {
 175     outptr = output_data[outrow];
 176     for (outcol = 0, outcol_h = 0; outcol < output_cols;
 177          outcol++, outcol_h += h_expand) {
 178       outvalue = 0;
 179       for (v = 0; v < v_expand; v++) {
 180         inptr = input_data[inrow+v] + outcol_h;
 181         for (h = 0; h < h_expand; h++) {
 182           outvalue += (INT32) GETJSAMPLE(*inptr++);
 183         }
 184       }
 185       *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
 186     }
 187     inrow += v_expand;
 188     outrow++;
 189   }
 190 }
 191
 192
 193 /*
 194  * Downsample pixel values of a single component.
 195  * This version handles the special case of a full-size component,
 196  * without smoothing.
 197  */
 198
 199 METHODDEF(void)
 200 fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 201                      JSAMPARRAY input_data, JSAMPARRAY output_data)
 202 {
 203   /* Copy the data */
 204   jcopy_sample_rows(input_data, output_data,
 205                     cinfo->max_v_samp_factor, cinfo->image_width);
 206   /* Edge-expand */
 207   expand_right_edge(output_data, cinfo->max_v_samp_factor, cinfo->image_width,
 208                     compptr->width_in_blocks * compptr->DCT_h_scaled_size);
 209 }
 210
 211
 212 /*
 213  * Downsample pixel values of a single component.
 214  * This version handles the common case of 2:1 horizontal and 1:1 vertical,
 215  * without smoothing.
 216  *
 217  * A note about the "bias" calculations: when rounding fractional values to
 218  * integer, we do not want to always round 0.5 up to the next integer.
 219  * If we did that, we'd introduce a noticeable bias towards larger values.
 220  * Instead, this code is arranged so that 0.5 will be rounded up or down at
 221  * alternate pixel locations (a simple ordered dither pattern).
 222  */
 223
 224 METHODDEF(void)
 225 h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 226                  JSAMPARRAY input_data, JSAMPARRAY output_data)
 227 {
 228   int inrow;
 229   JDIMENSION outcol;
 230   JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
 231   register JSAMPROW inptr, outptr;
 232   register int bias;
 233
 234   /* Expand input data enough to let all the output samples be generated
 235    * by the standard loop.  Special-casing padded output would be more
 236    * efficient.
 237    */
 238   expand_right_edge(input_data, cinfo->max_v_samp_factor,
 239                     cinfo->image_width, output_cols * 2);
 240
 241   for (inrow = 0; inrow < cinfo->max_v_samp_factor; inrow++) {
 242     outptr = output_data[inrow];
 243     inptr = input_data[inrow];
 244     bias = 0;                   /* bias = 0,1,0,1,... for successive samples */
 245     for (outcol = 0; outcol < output_cols; outcol++) {
 246       *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
 247                               + bias) >> 1);
 248       bias ^= 1;                /* 0=>1, 1=>0 */
 249       inptr += 2;
 250     }
 251   }
 252 }
 253
 254
 255 /*
 256  * Downsample pixel values of a single component.
 257  * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
 258  * without smoothing.
 259  */
 260
 261 METHODDEF(void)
 262 h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 263                  JSAMPARRAY input_data, JSAMPARRAY output_data)
 264 {
 265   int inrow, outrow;
 266   JDIMENSION outcol;
 267   JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
 268   register JSAMPROW inptr0, inptr1, outptr;
 269   register int bias;
 270
 271   /* Expand input data enough to let all the output samples be generated
 272    * by the standard loop.  Special-casing padded output would be more
 273    * efficient.
 274    */
 275   expand_right_edge(input_data, cinfo->max_v_samp_factor,
 276                     cinfo->image_width, output_cols * 2);
 277
 278   inrow = outrow = 0;
 279   while (inrow < cinfo->max_v_samp_factor) {
 280     outptr = output_data[outrow];
 281     inptr0 = input_data[inrow];
 282     inptr1 = input_data[inrow+1];
 283     bias = 1;                   /* bias = 1,2,1,2,... for successive samples */
 284     for (outcol = 0; outcol < output_cols; outcol++) {
 285       *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 286                               GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
 287                               + bias) >> 2);
 288       bias ^= 3;                /* 1=>2, 2=>1 */
 289       inptr0 += 2; inptr1 += 2;
 290     }
 291     inrow += 2;
 292     outrow++;
 293   }
 294 }
 295
 296
 297 #ifdef INPUT_SMOOTHING_SUPPORTED
 298
 299 /*
 300  * Downsample pixel values of a single component.
 301  * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
 302  * with smoothing.  One row of context is required.
 303  */
 304
 305 METHODDEF(void)
 306 h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 307                         JSAMPARRAY input_data, JSAMPARRAY output_data)
 308 {
 309   int inrow, outrow;
 310   JDIMENSION colctr;
 311   JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
 312   register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
 313   INT32 membersum, neighsum, memberscale, neighscale;
 314
 315   /* Expand input data enough to let all the output samples be generated
 316    * by the standard loop.  Special-casing padded output would be more
 317    * efficient.
 318    */
 319   expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
 320                     cinfo->image_width, output_cols * 2);
 321
 322   /* We don't bother to form the individual "smoothed" input pixel values;
 323    * we can directly compute the output which is the average of the four
 324    * smoothed values.  Each of the four member pixels contributes a fraction
 325    * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
 326    * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
 327    * output.  The four corner-adjacent neighbor pixels contribute a fraction
 328    * SF to just one smoothed pixel, or SF/4 to the final output; while the
 329    * eight edge-adjacent neighbors contribute SF to each of two smoothed
 330    * pixels, or SF/2 overall.  In order to use integer arithmetic, these
 331    * factors are scaled by 2^16 = 65536.
 332    * Also recall that SF = smoothing_factor / 1024.
 333    */
 334
 335   memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
 336   neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
 337
 338   inrow = outrow = 0;
 339   while (inrow < cinfo->max_v_samp_factor) {
 340     outptr = output_data[outrow];
 341     inptr0 = input_data[inrow];
 342     inptr1 = input_data[inrow+1];
 343     above_ptr = input_data[inrow-1];
 344     below_ptr = input_data[inrow+2];
 345
 346     /* Special case for first column: pretend column -1 is same as column 0 */
 347     membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 348                 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
 349     neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
 350                GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
 351                GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
 352                GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
 353     neighsum += neighsum;
 354     neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
 355                 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]);
 356     membersum = membersum * memberscale + neighsum * neighscale;
 357     *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 358     inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
 359
 360     for (colctr = output_cols - 2; colctr > 0; colctr--) {
 361       /* sum of pixels directly mapped to this output element */
 362       membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 363                   GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
 364       /* sum of edge-neighbor pixels */
 365       neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
 366                  GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
 367                  GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
 368                  GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
 369       /* The edge-neighbors count twice as much as corner-neighbors */
 370       neighsum += neighsum;
 371       /* Add in the corner-neighbors */
 372       neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
 373                   GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
 374       /* form final output scaled up by 2^16 */
 375       membersum = membersum * memberscale + neighsum * neighscale;
 376       /* round, descale and output it */
 377       *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 378       inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
 379     }
 380
 381     /* Special case for last column */
 382     membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 383                 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
 384     neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
 385                GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
 386                GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
 387                GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
 388     neighsum += neighsum;
 389     neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
 390                 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
 391     membersum = membersum * memberscale + neighsum * neighscale;
 392     *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
 393
 394     inrow += 2;
 395     outrow++;
 396   }
 397 }
 398
 399
 400 /*
 401  * Downsample pixel values of a single component.
 402  * This version handles the special case of a full-size component,
 403  * with smoothing.  One row of context is required.
 404  */
 405
 406 METHODDEF(void)
 407 fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
 408                             JSAMPARRAY input_data, JSAMPARRAY output_data)
 409 {
 410   int inrow;
 411   JDIMENSION colctr;
 412   JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;
 413   register JSAMPROW inptr, above_ptr, below_ptr, outptr;
 414   INT32 membersum, neighsum, memberscale, neighscale;
 415   int colsum, lastcolsum, nextcolsum;
 416
 417   /* Expand input data enough to let all the output samples be generated
 418    * by the standard loop.  Special-casing padded output would be more
 419    * efficient.
 420    */
 421   expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
 422                     cinfo->image_width, output_cols);
 423
 424   /* Each of the eight neighbor pixels contributes a fraction SF to the
 425    * smoothed pixel, while the main pixel contributes (1-8*SF).  In order
 426    * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
 427    * Also recall that SF = smoothing_factor / 1024.
 428    */
 429
 430   memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
 431   neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
 432
 433   for (inrow = 0; inrow < cinfo->max_v_samp_factor; inrow++) {
 434     outptr = output_data[inrow];
 435     inptr = input_data[inrow];
 436     above_ptr = input_data[inrow-1];
 437     below_ptr = input_data[inrow+1];
 438
 439     /* Special case for first column */
 440     colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
 441              GETJSAMPLE(*inptr);
 442     membersum = GETJSAMPLE(*inptr++);
 443     nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
 444                  GETJSAMPLE(*inptr);
 445     neighsum = colsum + (colsum - membersum) + nextcolsum;
 446     membersum = membersum * memberscale + neighsum * neighscale;
 447     *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 448     lastcolsum = colsum; colsum = nextcolsum;
 449
 450     for (colctr = output_cols - 2; colctr > 0; colctr--) {
 451       membersum = GETJSAMPLE(*inptr++);
 452       above_ptr++; below_ptr++;
 453       nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
 454                    GETJSAMPLE(*inptr);
 455       neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
 456       membersum = membersum * memberscale + neighsum * neighscale;
 457       *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 458       lastcolsum = colsum; colsum = nextcolsum;
 459     }
 460
 461     /* Special case for last column */
 462     membersum = GETJSAMPLE(*inptr);
 463     neighsum = lastcolsum + (colsum - membersum) + colsum;
 464     membersum = membersum * memberscale + neighsum * neighscale;
 465     *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
 466
 467   }
 468 }
 469
 470 #endif /* INPUT_SMOOTHING_SUPPORTED */
 471
 472
 473 /*
 474  * Module initialization routine for downsampling.
 475  * Note that we must select a routine for each component.
 476  */
 477
 478 GLOBAL(void)
 479 jinit_downsampler (j_compress_ptr cinfo)
 480 {
 481   my_downsample_ptr downsample;
 482   int ci;
 483   jpeg_component_info * compptr;
 484   boolean smoothok = TRUE;
 485   int h_in_group, v_in_group, h_out_group, v_out_group;
 486
 487   downsample = (my_downsample_ptr) (*cinfo->mem->alloc_small)
 488     ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(my_downsampler));
 489   cinfo->downsample = &downsample->pub;
 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 }