src/jpeg/jdmaster.c

   1 /*
   2  * jdmaster.c
   3  *
   4  * Copyright (C) 1991-1997, 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 master control logic for the JPEG decompressor.
   9  * These routines are concerned with selecting the modules to be executed
  10  * and with determining the number of passes and the work to be done in each
  11  * pass.
  12  */
  13
  14 #define JPEG_INTERNALS
  15 #include "jinclude.h"
  16 #include "jpeglib.h"
  17
  18 #if defined(__VISAGECPP__)
  19 /* Visual Age fixups for multiple declarations */
  20 #  define start_input_pass   start_input_pass2 /* already in jcmaint.c */
  21 #endif
  22
  23 /* Private state */
  24
  25 typedef struct {
  26   struct jpeg_decomp_master pub; /* public fields */
  27
  28   int pass_number;              /* # of passes completed */
  29
  30   boolean using_merged_upsample; /* TRUE if using merged upsample/cconvert */
  31
  32   /* Saved references to initialized quantizer modules,
  33    * in case we need to switch modes.
  34    */
  35   struct jpeg_color_quantizer * quantizer_1pass;
  36   struct jpeg_color_quantizer * quantizer_2pass;
  37 } my_decomp_master;
  38
  39 typedef my_decomp_master * my_master_ptr;
  40
  41
  42 /*
  43  * Determine whether merged upsample/color conversion should be used.
  44  * CRUCIAL: this must match the actual capabilities of jdmerge.c!
  45  */
  46
  47 LOCAL(boolean)
  48 use_merged_upsample (j_decompress_ptr cinfo)
  49 {
  50 #ifdef UPSAMPLE_MERGING_SUPPORTED
  51   /* Merging is the equivalent of plain box-filter upsampling */
  52   if (cinfo->do_fancy_upsampling || cinfo->CCIR601_sampling)
  53     return FALSE;
  54   /* jdmerge.c only supports YCC=>RGB color conversion */
  55   if (cinfo->jpeg_color_space != JCS_YCbCr || cinfo->num_components != 3 ||
  56       cinfo->out_color_space != JCS_RGB ||
  57       cinfo->out_color_components != RGB_PIXELSIZE)
  58     return FALSE;
  59   /* and it only handles 2h1v or 2h2v sampling ratios */
  60   if (cinfo->comp_info[0].h_samp_factor != 2 ||
  61       cinfo->comp_info[1].h_samp_factor != 1 ||
  62       cinfo->comp_info[2].h_samp_factor != 1 ||
  63       cinfo->comp_info[0].v_samp_factor >  2 ||
  64       cinfo->comp_info[1].v_samp_factor != 1 ||
  65       cinfo->comp_info[2].v_samp_factor != 1)
  66     return FALSE;
  67   /* furthermore, it doesn't work if we've scaled the IDCTs differently */
  68   if (cinfo->comp_info[0].DCT_scaled_size != cinfo->min_DCT_scaled_size ||
  69       cinfo->comp_info[1].DCT_scaled_size != cinfo->min_DCT_scaled_size ||
  70       cinfo->comp_info[2].DCT_scaled_size != cinfo->min_DCT_scaled_size)
  71     return FALSE;
  72   /* ??? also need to test for upsample-time rescaling, when & if supported */
  73   return TRUE;                  /* by golly, it'll work... */
  74 #else
  75   return FALSE;
  76 #endif
  77 }
  78
  79
  80 /*
  81  * Compute output image dimensions and related values.
  82  * NOTE: this is exported for possible use by application.
  83  * Hence it mustn't do anything that can't be done twice.
  84  * Also note that it may be called before the master module is initialized!
  85  */
  86
  87 GLOBAL(void)
  88 jpeg_calc_output_dimensions (j_decompress_ptr cinfo)
  89 /* Do computations that are needed before master selection phase */
  90 {
  91 #ifdef IDCT_SCALING_SUPPORTED
  92   int ci;
  93   jpeg_component_info *compptr;
  94 #endif
  95
  96   /* Prevent application from calling me at wrong times */
  97   if (cinfo->global_state != DSTATE_READY)
  98     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  99
 100 #ifdef IDCT_SCALING_SUPPORTED
 101
 102   /* Compute actual output image dimensions and DCT scaling choices. */
 103   if (cinfo->scale_num * 8 <= cinfo->scale_denom) {
 104     /* Provide 1/8 scaling */
 105     cinfo->output_width = (JDIMENSION)
 106       jdiv_round_up((long) cinfo->image_width, 8L);
 107     cinfo->output_height = (JDIMENSION)
 108       jdiv_round_up((long) cinfo->image_height, 8L);
 109     cinfo->min_DCT_scaled_size = 1;
 110   } else if (cinfo->scale_num * 4 <= cinfo->scale_denom) {
 111     /* Provide 1/4 scaling */
 112     cinfo->output_width = (JDIMENSION)
 113       jdiv_round_up((long) cinfo->image_width, 4L);
 114     cinfo->output_height = (JDIMENSION)
 115       jdiv_round_up((long) cinfo->image_height, 4L);
 116     cinfo->min_DCT_scaled_size = 2;
 117   } else if (cinfo->scale_num * 2 <= cinfo->scale_denom) {
 118     /* Provide 1/2 scaling */
 119     cinfo->output_width = (JDIMENSION)
 120       jdiv_round_up((long) cinfo->image_width, 2L);
 121     cinfo->output_height = (JDIMENSION)
 122       jdiv_round_up((long) cinfo->image_height, 2L);
 123     cinfo->min_DCT_scaled_size = 4;
 124   } else {
 125     /* Provide 1/1 scaling */
 126     cinfo->output_width = cinfo->image_width;
 127     cinfo->output_height = cinfo->image_height;
 128     cinfo->min_DCT_scaled_size = DCTSIZE;
 129   }
 130   /* In selecting the actual DCT scaling for each component, we try to
 131    * scale up the chroma components via IDCT scaling rather than upsampling.
 132    * This saves time if the upsampler gets to use 1:1 scaling.
 133    * Note this code assumes that the supported DCT scalings are powers of 2.
 134    */
 135   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 136        ci++, compptr++) {
 137     int ssize = cinfo->min_DCT_scaled_size;
 138     while (ssize < DCTSIZE &&
 139            (compptr->h_samp_factor * ssize * 2 <=
 140             cinfo->max_h_samp_factor * cinfo->min_DCT_scaled_size) &&
 141            (compptr->v_samp_factor * ssize * 2 <=
 142             cinfo->max_v_samp_factor * cinfo->min_DCT_scaled_size)) {
 143       ssize = ssize * 2;
 144     }
 145     compptr->DCT_scaled_size = ssize;
 146   }
 147
 148   /* Recompute downsampled dimensions of components;
 149    * application needs to know these if using raw downsampled data.
 150    */
 151   for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
 152        ci++, compptr++) {
 153     /* Size in samples, after IDCT scaling */
 154     compptr->downsampled_width = (JDIMENSION)
 155       jdiv_round_up((long) cinfo->image_width *
 156                     (long) (compptr->h_samp_factor * compptr->DCT_scaled_size),
 157                     (long) (cinfo->max_h_samp_factor * DCTSIZE));
 158     compptr->downsampled_height = (JDIMENSION)
 159       jdiv_round_up((long) cinfo->image_height *
 160                     (long) (compptr->v_samp_factor * compptr->DCT_scaled_size),
 161                     (long) (cinfo->max_v_samp_factor * DCTSIZE));
 162   }
 163
 164 #else /* !IDCT_SCALING_SUPPORTED */
 165
 166   /* Hardwire it to "no scaling" */
 167   cinfo->output_width = cinfo->image_width;
 168   cinfo->output_height = cinfo->image_height;
 169   /* jdinput.c has already initialized DCT_scaled_size to DCTSIZE,
 170    * and has computed unscaled downsampled_width and downsampled_height.
 171    */
 172
 173 #endif /* IDCT_SCALING_SUPPORTED */
 174
 175   /* Report number of components in selected colorspace. */
 176   /* Probably this should be in the color conversion module... */
 177   switch (cinfo->out_color_space) {
 178   case JCS_GRAYSCALE:
 179     cinfo->out_color_components = 1;
 180     break;
 181   case JCS_RGB:
 182 #if RGB_PIXELSIZE != 3
 183     cinfo->out_color_components = RGB_PIXELSIZE;
 184     break;
 185 #endif /* else share code with YCbCr */
 186   case JCS_YCbCr:
 187     cinfo->out_color_components = 3;
 188     break;
 189   case JCS_CMYK:
 190   case JCS_YCCK:
 191     cinfo->out_color_components = 4;
 192     break;
 193   default:                      /* else must be same colorspace as in file */
 194     cinfo->out_color_components = cinfo->num_components;
 195     break;
 196   }
 197   cinfo->output_components = (cinfo->quantize_colors ? 1 :
 198                               cinfo->out_color_components);
 199
 200   /* See if upsampler will want to emit more than one row at a time */
 201   if (use_merged_upsample(cinfo))
 202     cinfo->rec_outbuf_height = cinfo->max_v_samp_factor;
 203   else
 204     cinfo->rec_outbuf_height = 1;
 205 }
 206
 207
 208 /*
 209  * Several decompression processes need to range-limit values to the range
 210  * 0..MAXJSAMPLE; the input value may fall somewhat outside this range
 211  * due to noise introduced by quantization, roundoff error, etc.  These
 212  * processes are inner loops and need to be as fast as possible.  On most
 213  * machines, particularly CPUs with pipelines or instruction prefetch,
 214  * a (subscript-check-less) C table lookup
 215  *              x = sample_range_limit[x];
 216  * is faster than explicit tests
 217  *              if (x < 0)  x = 0;
 218  *              else if (x > MAXJSAMPLE)  x = MAXJSAMPLE;
 219  * These processes all use a common table prepared by the routine below.
 220  *
 221  * For most steps we can mathematically guarantee that the initial value
 222  * of x is within MAXJSAMPLE+1 of the legal range, so a table running from
 223  * -(MAXJSAMPLE+1) to 2*MAXJSAMPLE+1 is sufficient.  But for the initial
 224  * limiting step (just after the IDCT), a wildly out-of-range value is
 225  * possible if the input data is corrupt.  To avoid any chance of indexing
 226  * off the end of memory and getting a bad-pointer trap, we perform the
 227  * post-IDCT limiting thus:
 228  *              x = range_limit[x & MASK];
 229  * where MASK is 2 bits wider than legal sample data, ie 10 bits for 8-bit
 230  * samples.  Under normal circumstances this is more than enough range and
 231  * a correct output will be generated; with bogus input data the mask will
 232  * cause wraparound, and we will safely generate a bogus-but-in-range output.
 233  * For the post-IDCT step, we want to convert the data from signed to unsigned
 234  * representation by adding CENTERJSAMPLE at the same time that we limit it.
 235  * So the post-IDCT limiting table ends up looking like this:
 236  *   CENTERJSAMPLE,CENTERJSAMPLE+1,...,MAXJSAMPLE,
 237  *   MAXJSAMPLE (repeat 2*(MAXJSAMPLE+1)-CENTERJSAMPLE times),
 238  *   0          (repeat 2*(MAXJSAMPLE+1)-CENTERJSAMPLE times),
 239  *   0,1,...,CENTERJSAMPLE-1
 240  * Negative inputs select values from the upper half of the table after
 241  * masking.
 242  *
 243  * We can save some space by overlapping the start of the post-IDCT table
 244  * with the simpler range limiting table.  The post-IDCT table begins at
 245  * sample_range_limit + CENTERJSAMPLE.
 246  *
 247  * Note that the table is allocated in near data space on PCs; it's small
 248  * enough and used often enough to justify this.
 249  */
 250
 251 LOCAL(void)
 252 prepare_range_limit_table (j_decompress_ptr cinfo)
 253 /* Allocate and fill in the sample_range_limit table */
 254 {
 255   JSAMPLE * table;
 256   int i;
 257
 258   table = (JSAMPLE *)
 259     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 260                 (5 * (MAXJSAMPLE+1) + CENTERJSAMPLE) * SIZEOF(JSAMPLE));
 261   table += (MAXJSAMPLE+1);      /* allow negative subscripts of simple table */
 262   cinfo->sample_range_limit = table;
 263   /* First segment of "simple" table: limit[x] = 0 for x < 0 */
 264   MEMZERO(table - (MAXJSAMPLE+1), (MAXJSAMPLE+1) * SIZEOF(JSAMPLE));
 265   /* Main part of "simple" table: limit[x] = x */
 266   for (i = 0; i <= MAXJSAMPLE; i++)
 267     table[i] = (JSAMPLE) i;
 268   table += CENTERJSAMPLE;       /* Point to where post-IDCT table starts */
 269   /* End of simple table, rest of first half of post-IDCT table */
 270   for (i = CENTERJSAMPLE; i < 2*(MAXJSAMPLE+1); i++)
 271     table[i] = MAXJSAMPLE;
 272   /* Second half of post-IDCT table */
 273   MEMZERO(table + (2 * (MAXJSAMPLE+1)),
 274           (2 * (MAXJSAMPLE+1) - CENTERJSAMPLE) * SIZEOF(JSAMPLE));
 275   MEMCOPY(table + (4 * (MAXJSAMPLE+1) - CENTERJSAMPLE),
 276           cinfo->sample_range_limit, CENTERJSAMPLE * SIZEOF(JSAMPLE));
 277 }
 278
 279
 280 /*
 281  * Master selection of decompression modules.
 282  * This is done once at jpeg_start_decompress time.  We determine
 283  * which modules will be used and give them appropriate initialization calls.
 284  * We also initialize the decompressor input side to begin consuming data.
 285  *
 286  * Since jpeg_read_header has finished, we know what is in the SOF
 287  * and (first) SOS markers.  We also have all the application parameter
 288  * settings.
 289  */
 290
 291 LOCAL(void)
 292 master_selection (j_decompress_ptr cinfo)
 293 {
 294   my_master_ptr master = (my_master_ptr) cinfo->master;
 295   boolean use_c_buffer;
 296   long samplesperrow;
 297   JDIMENSION jd_samplesperrow;
 298
 299   /* Initialize dimensions and other stuff */
 300   jpeg_calc_output_dimensions(cinfo);
 301   prepare_range_limit_table(cinfo);
 302
 303   /* Width of an output scanline must be representable as JDIMENSION. */
 304   samplesperrow = (long) cinfo->output_width * (long) cinfo->out_color_components;
 305   jd_samplesperrow = (JDIMENSION) samplesperrow;
 306   if ((long) jd_samplesperrow != samplesperrow)
 307     ERREXIT(cinfo, JERR_WIDTH_OVERFLOW);
 308
 309   /* Initialize my private state */
 310   master->pass_number = 0;
 311   master->using_merged_upsample = use_merged_upsample(cinfo);
 312
 313   /* Color quantizer selection */
 314   master->quantizer_1pass = NULL;
 315   master->quantizer_2pass = NULL;
 316   /* No mode changes if not using buffered-image mode. */
 317   if (! cinfo->quantize_colors || ! cinfo->buffered_image) {
 318     cinfo->enable_1pass_quant = FALSE;
 319     cinfo->enable_external_quant = FALSE;
 320     cinfo->enable_2pass_quant = FALSE;
 321   }
 322   if (cinfo->quantize_colors) {
 323     if (cinfo->raw_data_out)
 324       ERREXIT(cinfo, JERR_NOTIMPL);
 325     /* 2-pass quantizer only works in 3-component color space. */
 326     if (cinfo->out_color_components != 3) {
 327       cinfo->enable_1pass_quant = TRUE;
 328       cinfo->enable_external_quant = FALSE;
 329       cinfo->enable_2pass_quant = FALSE;
 330       cinfo->colormap = NULL;
 331     } else if (cinfo->colormap != NULL) {
 332       cinfo->enable_external_quant = TRUE;
 333     } else if (cinfo->two_pass_quantize) {
 334       cinfo->enable_2pass_quant = TRUE;
 335     } else {
 336       cinfo->enable_1pass_quant = TRUE;
 337     }
 338
 339     if (cinfo->enable_1pass_quant) {
 340 #ifdef QUANT_1PASS_SUPPORTED
 341       jinit_1pass_quantizer(cinfo);
 342       master->quantizer_1pass = cinfo->cquantize;
 343 #else
 344       ERREXIT(cinfo, JERR_NOT_COMPILED);
 345 #endif
 346     }
 347
 348     /* We use the 2-pass code to map to external colormaps. */
 349     if (cinfo->enable_2pass_quant || cinfo->enable_external_quant) {
 350 #ifdef QUANT_2PASS_SUPPORTED
 351       jinit_2pass_quantizer(cinfo);
 352       master->quantizer_2pass = cinfo->cquantize;
 353 #else
 354       ERREXIT(cinfo, JERR_NOT_COMPILED);
 355 #endif
 356     }
 357     /* If both quantizers are initialized, the 2-pass one is left active;
 358      * this is necessary for starting with quantization to an external map.
 359      */
 360   }
 361
 362   /* Post-processing: in particular, color conversion first */
 363   if (! cinfo->raw_data_out) {
 364     if (master->using_merged_upsample) {
 365 #ifdef UPSAMPLE_MERGING_SUPPORTED
 366       jinit_merged_upsampler(cinfo); /* does color conversion too */
 367 #else
 368       ERREXIT(cinfo, JERR_NOT_COMPILED);
 369 #endif
 370     } else {
 371       jinit_color_deconverter(cinfo);
 372       jinit_upsampler(cinfo);
 373     }
 374     jinit_d_post_controller(cinfo, cinfo->enable_2pass_quant);
 375   }
 376   /* Inverse DCT */
 377   jinit_inverse_dct(cinfo);
 378   /* Entropy decoding: either Huffman or arithmetic coding. */
 379   if (cinfo->arith_code) {
 380     ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
 381   } else {
 382     if (cinfo->progressive_mode) {
 383 #ifdef D_PROGRESSIVE_SUPPORTED
 384       jinit_phuff_decoder(cinfo);
 385 #else
 386       ERREXIT(cinfo, JERR_NOT_COMPILED);
 387 #endif
 388     } else
 389       jinit_huff_decoder(cinfo);
 390   }
 391
 392   /* Initialize principal buffer controllers. */
 393   use_c_buffer = cinfo->inputctl->has_multiple_scans || cinfo->buffered_image;
 394   jinit_d_coef_controller(cinfo, use_c_buffer);
 395
 396   if (! cinfo->raw_data_out)
 397     jinit_d_main_controller(cinfo, FALSE /* never need full buffer here */);
 398
 399   /* We can now tell the memory manager to allocate virtual arrays. */
 400   (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
 401
 402   /* Initialize input side of decompressor to consume first scan. */
 403   (*cinfo->inputctl->start_input_pass) (cinfo);
 404
 405 #ifdef D_MULTISCAN_FILES_SUPPORTED
 406   /* If jpeg_start_decompress will read the whole file, initialize
 407    * progress monitoring appropriately.  The input step is counted
 408    * as one pass.
 409    */
 410   if (cinfo->progress != NULL && ! cinfo->buffered_image &&
 411       cinfo->inputctl->has_multiple_scans) {
 412     int nscans;
 413     /* Estimate number of scans to set pass_limit. */
 414     if (cinfo->progressive_mode) {
 415       /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
 416       nscans = 2 + 3 * cinfo->num_components;
 417     } else {
 418       /* For a nonprogressive multiscan file, estimate 1 scan per component. */
 419       nscans = cinfo->num_components;
 420     }
 421     cinfo->progress->pass_counter = 0L;
 422     cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
 423     cinfo->progress->completed_passes = 0;
 424     cinfo->progress->total_passes = (cinfo->enable_2pass_quant ? 3 : 2);
 425     /* Count the input pass as done */
 426     master->pass_number++;
 427   }
 428 #endif /* D_MULTISCAN_FILES_SUPPORTED */
 429 }
 430
 431
 432 /*
 433  * Per-pass setup.
 434  * This is called at the beginning of each output pass.  We determine which
 435  * modules will be active during this pass and give them appropriate
 436  * start_pass calls.  We also set is_dummy_pass to indicate whether this
 437  * is a "real" output pass or a dummy pass for color quantization.
 438  * (In the latter case, jdapistd.c will crank the pass to completion.)
 439  */
 440
 441 METHODDEF(void)
 442 prepare_for_output_pass (j_decompress_ptr cinfo)
 443 {
 444   my_master_ptr master = (my_master_ptr) cinfo->master;
 445
 446   if (master->pub.is_dummy_pass) {
 447 #ifdef QUANT_2PASS_SUPPORTED
 448     /* Final pass of 2-pass quantization */
 449     master->pub.is_dummy_pass = FALSE;
 450     (*cinfo->cquantize->start_pass) (cinfo, FALSE);
 451     (*cinfo->post->start_pass) (cinfo, JBUF_CRANK_DEST);
 452     (*cinfo->main->start_pass) (cinfo, JBUF_CRANK_DEST);
 453 #else
 454     ERREXIT(cinfo, JERR_NOT_COMPILED);
 455 #endif /* QUANT_2PASS_SUPPORTED */
 456   } else {
 457     if (cinfo->quantize_colors && cinfo->colormap == NULL) {
 458       /* Select new quantization method */
 459       if (cinfo->two_pass_quantize && cinfo->enable_2pass_quant) {
 460         cinfo->cquantize = master->quantizer_2pass;
 461         master->pub.is_dummy_pass = TRUE;
 462       } else if (cinfo->enable_1pass_quant) {
 463         cinfo->cquantize = master->quantizer_1pass;
 464       } else {
 465         ERREXIT(cinfo, JERR_MODE_CHANGE);
 466       }
 467     }
 468     (*cinfo->idct->start_pass) (cinfo);
 469     (*cinfo->coef->start_output_pass) (cinfo);
 470     if (! cinfo->raw_data_out) {
 471       if (! master->using_merged_upsample)
 472         (*cinfo->cconvert->start_pass) (cinfo);
 473       (*cinfo->upsample->start_pass) (cinfo);
 474       if (cinfo->quantize_colors)
 475         (*cinfo->cquantize->start_pass) (cinfo, master->pub.is_dummy_pass);
 476       (*cinfo->post->start_pass) (cinfo,
 477             (master->pub.is_dummy_pass ? JBUF_SAVE_AND_PASS : JBUF_PASS_THRU));
 478       (*cinfo->main->start_pass) (cinfo, JBUF_PASS_THRU);
 479     }
 480   }
 481
 482   /* Set up progress monitor's pass info if present */
 483   if (cinfo->progress != NULL) {
 484     cinfo->progress->completed_passes = master->pass_number;
 485     cinfo->progress->total_passes = master->pass_number +
 486                                     (master->pub.is_dummy_pass ? 2 : 1);
 487     /* In buffered-image mode, we assume one more output pass if EOI not
 488      * yet reached, but no more passes if EOI has been reached.
 489      */
 490     if (cinfo->buffered_image && ! cinfo->inputctl->eoi_reached) {
 491       cinfo->progress->total_passes += (cinfo->enable_2pass_quant ? 2 : 1);
 492     }
 493   }
 494 }
 495
 496
 497 /*
 498  * Finish up at end of an output pass.
 499  */
 500
 501 METHODDEF(void)
 502 finish_output_pass (j_decompress_ptr cinfo)
 503 {
 504   my_master_ptr master = (my_master_ptr) cinfo->master;
 505
 506   if (cinfo->quantize_colors)
 507     (*cinfo->cquantize->finish_pass) (cinfo);
 508   master->pass_number++;
 509 }
 510
 511
 512 #ifdef D_MULTISCAN_FILES_SUPPORTED
 513
 514 /*
 515  * Switch to a new external colormap between output passes.
 516  */
 517
 518 GLOBAL(void)
 519 jpeg_new_colormap (j_decompress_ptr cinfo)
 520 {
 521   my_master_ptr master = (my_master_ptr) cinfo->master;
 522
 523   /* Prevent application from calling me at wrong times */
 524   if (cinfo->global_state != DSTATE_BUFIMAGE)
 525     ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
 526
 527   if (cinfo->quantize_colors && cinfo->enable_external_quant &&
 528       cinfo->colormap != NULL) {
 529     /* Select 2-pass quantizer for external colormap use */
 530     cinfo->cquantize = master->quantizer_2pass;
 531     /* Notify quantizer of colormap change */
 532     (*cinfo->cquantize->new_color_map) (cinfo);
 533     master->pub.is_dummy_pass = FALSE; /* just in case */
 534   } else
 535     ERREXIT(cinfo, JERR_MODE_CHANGE);
 536 }
 537
 538 #endif /* D_MULTISCAN_FILES_SUPPORTED */
 539
 540
 541 /*
 542  * Initialize master decompression control and select active modules.
 543  * This is performed at the start of jpeg_start_decompress.
 544  */
 545
 546 GLOBAL(void)
 547 jinit_master_decompress (j_decompress_ptr cinfo)
 548 {
 549   my_master_ptr master;
 550
 551   master = (my_master_ptr)
 552       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 553                                   SIZEOF(my_decomp_master));
 554   cinfo->master = (struct jpeg_decomp_master *) master;
 555   master->pub.prepare_for_output_pass = prepare_for_output_pass;
 556   master->pub.finish_output_pass = finish_output_pass;
 557
 558   master->pub.is_dummy_pass = FALSE;
 559
 560   master_selection(cinfo);
 561 }
 562
 563 #if defined(__VISAGECPP__)
 564 #  ifdef start_input_pass2
 565 #   undef start_input_pass2
 566 #  endif
 567 #endif
 568