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