media/libjpeg/jcsample.c

   1 /*
   2  * jcsample.c
   3  *
   4  * Copyright (C) 1991-1996, Thomas G. Lane.
   5  * Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
   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 #include "jsimd.h"
  53
  54
  55 /* Pointer to routine to downsample a single component */
  56 typedef JMETHOD(void, downsample1_ptr,
  57                 (j_compress_ptr cinfo, jpeg_component_info * compptr,
  58                  JSAMPARRAY input_data, JSAMPARRAY output_data));
  59
  60 /* Private subobject */
  61
  62 typedef struct {
  63   struct jpeg_downsampler pub;  /* public fields */
  64
  65   /* Downsampling method pointers, one per component */
  66   downsample1_ptr methods[MAX_COMPONENTS];
  67 } my_downsampler;
  68
  69 typedef my_downsampler * my_downsample_ptr;
  70
  71
  72 /*
  73  * Initialize for a downsampling pass.
  74  */
  75
  76 METHODDEF(void)
  77 start_pass_downsample (j_compress_ptr cinfo)
  78 {
  79   /* no work for now */
  80 }
  81
  82
  83 /*
  84  * Expand a component horizontally from width input_cols to width output_cols,
  85  * by duplicating the rightmost samples.
  86  */
  87
  88 LOCAL(void)
  89 expand_right_edge (JSAMPARRAY image_data, int num_rows,
  90                    JDIMENSION input_cols, JDIMENSION output_cols)
  91 {
  92   register JSAMPROW ptr;
  93   register JSAMPLE pixval;
  94   register int count;
  95   int row;
  96   int numcols = (int) (output_cols - input_cols);
  97
  98   if (numcols > 0) {
  99     for (row = 0; row < num_rows; row++) {
 100       ptr = image_data[row] + input_cols;
 101       pixval = ptr[-1];         /* don't need GETJSAMPLE() here */
 102       for (count = numcols; count > 0; count--)
 103         *ptr++ = pixval;
 104     }
 105   }
 106 }
 107
 108
 109 /*
 110  * Do downsampling for a whole row group (all components).
 111  *
 112  * In this version we simply downsample each component independently.
 113  */
 114
 115 METHODDEF(void)
 116 sep_downsample (j_compress_ptr cinfo,
 117                 JSAMPIMAGE input_buf, JDIMENSION in_row_index,
 118                 JSAMPIMAGE output_buf, JDIMENSION out_row_group_index)
 119 {
 120   my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
 121   int ci;
 122   jpeg_component_info * compptr;
 123   JSAMPARRAY in_ptr, out_ptr;
 124
 125   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 126        ci++, compptr++) {
 127     in_ptr = input_buf[ci] + in_row_index;
 128     out_ptr = output_buf[ci] + (out_row_group_index * compptr->v_samp_factor);
 129     (*downsample->methods[ci]) (cinfo, compptr, in_ptr, out_ptr);
 130   }
 131 }
 132
 133
 134 /*
 135  * Downsample pixel values of a single component.
 136  * One row group is processed per call.
 137  * This version handles arbitrary integral sampling ratios, without smoothing.
 138  * Note that this version is not actually used for customary sampling ratios.
 139  */
 140
 141 METHODDEF(void)
 142 int_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 143                 JSAMPARRAY input_data, JSAMPARRAY output_data)
 144 {
 145   int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
 146   JDIMENSION outcol, outcol_h;  /* outcol_h == outcol*h_expand */
 147   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
 148   JSAMPROW inptr, outptr;
 149   INT32 outvalue;
 150
 151   h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
 152   v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
 153   numpix = h_expand * v_expand;
 154   numpix2 = numpix/2;
 155
 156   /* Expand input data enough to let all the output samples be generated
 157    * by the standard loop.  Special-casing padded output would be more
 158    * efficient.
 159    */
 160   expand_right_edge(input_data, cinfo->max_v_samp_factor,
 161                     cinfo->image_width, output_cols * h_expand);
 162
 163   inrow = 0;
 164   for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
 165     outptr = output_data[outrow];
 166     for (outcol = 0, outcol_h = 0; outcol < output_cols;
 167          outcol++, outcol_h += h_expand) {
 168       outvalue = 0;
 169       for (v = 0; v < v_expand; v++) {
 170         inptr = input_data[inrow+v] + outcol_h;
 171         for (h = 0; h < h_expand; h++) {
 172           outvalue += (INT32) GETJSAMPLE(*inptr++);
 173         }
 174       }
 175       *outptr++ = (JSAMPLE) ((outvalue + numpix2) / numpix);
 176     }
 177     inrow += v_expand;
 178   }
 179 }
 180
 181
 182 /*
 183  * Downsample pixel values of a single component.
 184  * This version handles the special case of a full-size component,
 185  * without smoothing.
 186  */
 187
 188 METHODDEF(void)
 189 fullsize_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 190                      JSAMPARRAY input_data, JSAMPARRAY output_data)
 191 {
 192   /* Copy the data */
 193   jcopy_sample_rows(input_data, 0, output_data, 0,
 194                     cinfo->max_v_samp_factor, cinfo->image_width);
 195   /* Edge-expand */
 196   expand_right_edge(output_data, cinfo->max_v_samp_factor,
 197                     cinfo->image_width, compptr->width_in_blocks * DCTSIZE);
 198 }
 199
 200
 201 /*
 202  * Downsample pixel values of a single component.
 203  * This version handles the common case of 2:1 horizontal and 1:1 vertical,
 204  * without smoothing.
 205  *
 206  * A note about the "bias" calculations: when rounding fractional values to
 207  * integer, we do not want to always round 0.5 up to the next integer.
 208  * If we did that, we'd introduce a noticeable bias towards larger values.
 209  * Instead, this code is arranged so that 0.5 will be rounded up or down at
 210  * alternate pixel locations (a simple ordered dither pattern).
 211  */
 212
 213 METHODDEF(void)
 214 h2v1_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 215                  JSAMPARRAY input_data, JSAMPARRAY output_data)
 216 {
 217   int outrow;
 218   JDIMENSION outcol;
 219   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
 220   register JSAMPROW inptr, outptr;
 221   register int bias;
 222
 223   /* Expand input data enough to let all the output samples be generated
 224    * by the standard loop.  Special-casing padded output would be more
 225    * efficient.
 226    */
 227   expand_right_edge(input_data, cinfo->max_v_samp_factor,
 228                     cinfo->image_width, output_cols * 2);
 229
 230   for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
 231     outptr = output_data[outrow];
 232     inptr = input_data[outrow];
 233     bias = 0;                   /* bias = 0,1,0,1,... for successive samples */
 234     for (outcol = 0; outcol < output_cols; outcol++) {
 235       *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr) + GETJSAMPLE(inptr[1])
 236                               + bias) >> 1);
 237       bias ^= 1;                /* 0=>1, 1=>0 */
 238       inptr += 2;
 239     }
 240   }
 241 }
 242
 243
 244 /*
 245  * Downsample pixel values of a single component.
 246  * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
 247  * without smoothing.
 248  */
 249
 250 METHODDEF(void)
 251 h2v2_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 252                  JSAMPARRAY input_data, JSAMPARRAY output_data)
 253 {
 254   int inrow, outrow;
 255   JDIMENSION outcol;
 256   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
 257   register JSAMPROW inptr0, inptr1, outptr;
 258   register int bias;
 259
 260   /* Expand input data enough to let all the output samples be generated
 261    * by the standard loop.  Special-casing padded output would be more
 262    * efficient.
 263    */
 264   expand_right_edge(input_data, cinfo->max_v_samp_factor,
 265                     cinfo->image_width, output_cols * 2);
 266
 267   inrow = 0;
 268   for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
 269     outptr = output_data[outrow];
 270     inptr0 = input_data[inrow];
 271     inptr1 = input_data[inrow+1];
 272     bias = 1;                   /* bias = 1,2,1,2,... for successive samples */
 273     for (outcol = 0; outcol < output_cols; outcol++) {
 274       *outptr++ = (JSAMPLE) ((GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 275                               GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1])
 276                               + bias) >> 2);
 277       bias ^= 3;                /* 1=>2, 2=>1 */
 278       inptr0 += 2; inptr1 += 2;
 279     }
 280     inrow += 2;
 281   }
 282 }
 283
 284
 285 #ifdef INPUT_SMOOTHING_SUPPORTED
 286
 287 /*
 288  * Downsample pixel values of a single component.
 289  * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
 290  * with smoothing.  One row of context is required.
 291  */
 292
 293 METHODDEF(void)
 294 h2v2_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info * compptr,
 295                         JSAMPARRAY input_data, JSAMPARRAY output_data)
 296 {
 297   int inrow, outrow;
 298   JDIMENSION colctr;
 299   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
 300   register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
 301   INT32 membersum, neighsum, memberscale, neighscale;
 302
 303   /* Expand input data enough to let all the output samples be generated
 304    * by the standard loop.  Special-casing padded output would be more
 305    * efficient.
 306    */
 307   expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
 308                     cinfo->image_width, output_cols * 2);
 309
 310   /* We don't bother to form the individual "smoothed" input pixel values;
 311    * we can directly compute the output which is the average of the four
 312    * smoothed values.  Each of the four member pixels contributes a fraction
 313    * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
 314    * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
 315    * output.  The four corner-adjacent neighbor pixels contribute a fraction
 316    * SF to just one smoothed pixel, or SF/4 to the final output; while the
 317    * eight edge-adjacent neighbors contribute SF to each of two smoothed
 318    * pixels, or SF/2 overall.  In order to use integer arithmetic, these
 319    * factors are scaled by 2^16 = 65536.
 320    * Also recall that SF = smoothing_factor / 1024.
 321    */
 322
 323   memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
 324   neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */
 325
 326   inrow = 0;
 327   for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
 328     outptr = output_data[outrow];
 329     inptr0 = input_data[inrow];
 330     inptr1 = input_data[inrow+1];
 331     above_ptr = input_data[inrow-1];
 332     below_ptr = input_data[inrow+2];
 333
 334     /* Special case for first column: pretend column -1 is same as column 0 */
 335     membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 336                 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
 337     neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
 338                GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
 339                GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[2]) +
 340                GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[2]);
 341     neighsum += neighsum;
 342     neighsum += GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[2]) +
 343                 GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[2]);
 344     membersum = membersum * memberscale + neighsum * neighscale;
 345     *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 346     inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
 347
 348     for (colctr = output_cols - 2; colctr > 0; colctr--) {
 349       /* sum of pixels directly mapped to this output element */
 350       membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 351                   GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
 352       /* sum of edge-neighbor pixels */
 353       neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
 354                  GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
 355                  GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[2]) +
 356                  GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[2]);
 357       /* The edge-neighbors count twice as much as corner-neighbors */
 358       neighsum += neighsum;
 359       /* Add in the corner-neighbors */
 360       neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[2]) +
 361                   GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[2]);
 362       /* form final output scaled up by 2^16 */
 363       membersum = membersum * memberscale + neighsum * neighscale;
 364       /* round, descale and output it */
 365       *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 366       inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
 367     }
 368
 369     /* Special case for last column */
 370     membersum = GETJSAMPLE(*inptr0) + GETJSAMPLE(inptr0[1]) +
 371                 GETJSAMPLE(*inptr1) + GETJSAMPLE(inptr1[1]);
 372     neighsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(above_ptr[1]) +
 373                GETJSAMPLE(*below_ptr) + GETJSAMPLE(below_ptr[1]) +
 374                GETJSAMPLE(inptr0[-1]) + GETJSAMPLE(inptr0[1]) +
 375                GETJSAMPLE(inptr1[-1]) + GETJSAMPLE(inptr1[1]);
 376     neighsum += neighsum;
 377     neighsum += GETJSAMPLE(above_ptr[-1]) + GETJSAMPLE(above_ptr[1]) +
 378                 GETJSAMPLE(below_ptr[-1]) + GETJSAMPLE(below_ptr[1]);
 379     membersum = membersum * memberscale + neighsum * neighscale;
 380     *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
 381
 382     inrow += 2;
 383   }
 384 }
 385
 386
 387 /*
 388  * Downsample pixel values of a single component.
 389  * This version handles the special case of a full-size component,
 390  * with smoothing.  One row of context is required.
 391  */
 392
 393 METHODDEF(void)
 394 fullsize_smooth_downsample (j_compress_ptr cinfo, jpeg_component_info *compptr,
 395                             JSAMPARRAY input_data, JSAMPARRAY output_data)
 396 {
 397   int outrow;
 398   JDIMENSION colctr;
 399   JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
 400   register JSAMPROW inptr, above_ptr, below_ptr, outptr;
 401   INT32 membersum, neighsum, memberscale, neighscale;
 402   int colsum, lastcolsum, nextcolsum;
 403
 404   /* Expand input data enough to let all the output samples be generated
 405    * by the standard loop.  Special-casing padded output would be more
 406    * efficient.
 407    */
 408   expand_right_edge(input_data - 1, cinfo->max_v_samp_factor + 2,
 409                     cinfo->image_width, output_cols);
 410
 411   /* Each of the eight neighbor pixels contributes a fraction SF to the
 412    * smoothed pixel, while the main pixel contributes (1-8*SF).  In order
 413    * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
 414    * Also recall that SF = smoothing_factor / 1024.
 415    */
 416
 417   memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
 418   neighscale = cinfo->smoothing_factor * 64; /* scaled SF */
 419
 420   for (outrow = 0; outrow < compptr->v_samp_factor; outrow++) {
 421     outptr = output_data[outrow];
 422     inptr = input_data[outrow];
 423     above_ptr = input_data[outrow-1];
 424     below_ptr = input_data[outrow+1];
 425
 426     /* Special case for first column */
 427     colsum = GETJSAMPLE(*above_ptr++) + GETJSAMPLE(*below_ptr++) +
 428              GETJSAMPLE(*inptr);
 429     membersum = GETJSAMPLE(*inptr++);
 430     nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
 431                  GETJSAMPLE(*inptr);
 432     neighsum = colsum + (colsum - membersum) + nextcolsum;
 433     membersum = membersum * memberscale + neighsum * neighscale;
 434     *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 435     lastcolsum = colsum; colsum = nextcolsum;
 436
 437     for (colctr = output_cols - 2; colctr > 0; colctr--) {
 438       membersum = GETJSAMPLE(*inptr++);
 439       above_ptr++; below_ptr++;
 440       nextcolsum = GETJSAMPLE(*above_ptr) + GETJSAMPLE(*below_ptr) +
 441                    GETJSAMPLE(*inptr);
 442       neighsum = lastcolsum + (colsum - membersum) + nextcolsum;
 443       membersum = membersum * memberscale + neighsum * neighscale;
 444       *outptr++ = (JSAMPLE) ((membersum + 32768) >> 16);
 445       lastcolsum = colsum; colsum = nextcolsum;
 446     }
 447
 448     /* Special case for last column */
 449     membersum = GETJSAMPLE(*inptr);
 450     neighsum = lastcolsum + (colsum - membersum) + colsum;
 451     membersum = membersum * memberscale + neighsum * neighscale;
 452     *outptr = (JSAMPLE) ((membersum + 32768) >> 16);
 453
 454   }
 455 }
 456
 457 #endif /* INPUT_SMOOTHING_SUPPORTED */
 458
 459
 460 /*
 461  * Module initialization routine for downsampling.
 462  * Note that we must select a routine for each component.
 463  */
 464
 465 GLOBAL(void)
 466 jinit_downsampler (j_compress_ptr cinfo)
 467 {
 468   my_downsample_ptr downsample;
 469   int ci;
 470   jpeg_component_info * compptr;
 471   boolean smoothok = TRUE;
 472
 473   downsample = (my_downsample_ptr)
 474     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 475                                 SIZEOF(my_downsampler));
 476   cinfo->downsample = (struct jpeg_downsampler *) downsample;
 477   downsample->pub.start_pass = start_pass_downsample;
 478   downsample->pub.downsample = sep_downsample;
 479   downsample->pub.need_context_rows = FALSE;
 480
 481   if (cinfo->CCIR601_sampling)
 482     ERREXIT(cinfo, JERR_CCIR601_NOTIMPL);
 483
 484   /* Verify we can handle the sampling factors, and set up method pointers */
 485   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 486        ci++, compptr++) {
 487     if (compptr->h_samp_factor == cinfo->max_h_samp_factor &&
 488         compptr->v_samp_factor == cinfo->max_v_samp_factor) {
 489 #ifdef INPUT_SMOOTHING_SUPPORTED
 490       if (cinfo->smoothing_factor) {
 491         downsample->methods[ci] = fullsize_smooth_downsample;
 492         downsample->pub.need_context_rows = TRUE;
 493       } else
 494 #endif
 495         downsample->methods[ci] = fullsize_downsample;
 496     } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
 497                compptr->v_samp_factor == cinfo->max_v_samp_factor) {
 498       smoothok = FALSE;
 499       if (jsimd_can_h2v1_downsample())
 500         downsample->methods[ci] = jsimd_h2v1_downsample;
 501       else
 502         downsample->methods[ci] = h2v1_downsample;
 503     } else if (compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
 504                compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor) {
 505 #ifdef INPUT_SMOOTHING_SUPPORTED
 506       if (cinfo->smoothing_factor) {
 507         downsample->methods[ci] = h2v2_smooth_downsample;
 508         downsample->pub.need_context_rows = TRUE;
 509       } else
 510 #endif
 511         if (jsimd_can_h2v2_downsample())
 512           downsample->methods[ci] = jsimd_h2v2_downsample;
 513         else
 514           downsample->methods[ci] = h2v2_downsample;
 515     } else if ((cinfo->max_h_samp_factor % compptr->h_samp_factor) == 0 &&
 516                (cinfo->max_v_samp_factor % compptr->v_samp_factor) == 0) {
 517       smoothok = FALSE;
 518       downsample->methods[ci] = int_downsample;
 519     } else
 520       ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);
 521   }
 522
 523 #ifdef INPUT_SMOOTHING_SUPPORTED
 524   if (cinfo->smoothing_factor && !smoothok)
 525     TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);
 526 #endif
 527 }