src/jpeg/jdtrans.c

   1 /*
   2  * jdtrans.c
   3  *
   4  * Copyright (C) 1995-1997, 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 library routines for transcoding decompression,
   9  * that is, reading raw DCT coefficient arrays from an input JPEG file.
  10  * The routines in jdapimin.c will also be needed by a transcoder.
  11  */
  12
  13 #define JPEG_INTERNALS
  14 #include "jinclude.h"
  15 #include "jpeglib.h"
  16
  17
  18 /* Forward declarations */
  19 LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo));
  20
  21
  22 /*
  23  * Read the coefficient arrays from a JPEG file.
  24  * jpeg_read_header must be completed before calling this.
  25  *
  26  * The entire image is read into a set of virtual coefficient-block arrays,
  27  * one per component.  The return value is a pointer to the array of
  28  * virtual-array descriptors.  These can be manipulated directly via the
  29  * JPEG memory manager, or handed off to jpeg_write_coefficients().
  30  * To release the memory occupied by the virtual arrays, call
  31  * jpeg_finish_decompress() when done with the data.
  32  *
  33  * An alternative usage is to simply obtain access to the coefficient arrays
  34  * during a buffered-image-mode decompression operation.  This is allowed
  35  * after any jpeg_finish_output() call.  The arrays can be accessed until
  36  * jpeg_finish_decompress() is called.  (Note that any call to the library
  37  * may reposition the arrays, so don't rely on access_virt_barray() results
  38  * to stay valid across library calls.)
  39  *
  40  * Returns NULL if suspended.  This case need be checked only if
  41  * a suspending data source is used.
  42  */
  43
  44 GLOBAL(jvirt_barray_ptr *)
  45 jpeg_read_coefficients (j_decompress_ptr cinfo)
  46 {
  47   if (cinfo->global_state == DSTATE_READY) {
  48     /* First call: initialize active modules */
  49     transdecode_master_selection(cinfo);
  50     cinfo->global_state = DSTATE_RDCOEFS;
  51   }
  52   if (cinfo->global_state == DSTATE_RDCOEFS) {
  53     /* Absorb whole file into the coef buffer */
  54     for (;;) {
  55       int retcode;
  56       /* Call progress monitor hook if present */
  57       if (cinfo->progress != NULL)
  58         (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
  59       /* Absorb some more input */
  60       retcode = (*cinfo->inputctl->consume_input) (cinfo);
  61       if (retcode == JPEG_SUSPENDED)
  62         return NULL;
  63       if (retcode == JPEG_REACHED_EOI)
  64         break;
  65       /* Advance progress counter if appropriate */
  66       if (cinfo->progress != NULL &&
  67           (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
  68         if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
  69           /* startup underestimated number of scans; ratchet up one scan */
  70           cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
  71         }
  72       }
  73     }
  74     /* Set state so that jpeg_finish_decompress does the right thing */
  75     cinfo->global_state = DSTATE_STOPPING;
  76   }
  77   /* At this point we should be in state DSTATE_STOPPING if being used
  78    * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access
  79    * to the coefficients during a full buffered-image-mode decompression.
  80    */
  81   if ((cinfo->global_state == DSTATE_STOPPING ||
  82        cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) {
  83     return cinfo->coef->coef_arrays;
  84   }
  85   /* Oops, improper usage */
  86   ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
  87   return NULL;                  /* keep compiler happy */
  88 }
  89
  90
  91 /*
  92  * Master selection of decompression modules for transcoding.
  93  * This substitutes for jdmaster.c's initialization of the full decompressor.
  94  */
  95
  96 LOCAL(void)
  97 transdecode_master_selection (j_decompress_ptr cinfo)
  98 {
  99   /* This is effectively a buffered-image operation. */
 100   cinfo->buffered_image = TRUE;
 101
 102   /* Entropy decoding: either Huffman or arithmetic coding. */
 103   if (cinfo->arith_code) {
 104     ERREXIT(cinfo, JERR_ARITH_NOTIMPL);
 105   } else {
 106     if (cinfo->progressive_mode) {
 107 #ifdef D_PROGRESSIVE_SUPPORTED
 108       jinit_phuff_decoder(cinfo);
 109 #else
 110       ERREXIT(cinfo, JERR_NOT_COMPILED);
 111 #endif
 112     } else
 113       jinit_huff_decoder(cinfo);
 114   }
 115
 116   /* Always get a full-image coefficient buffer. */
 117   jinit_d_coef_controller(cinfo, TRUE);
 118
 119   /* We can now tell the memory manager to allocate virtual arrays. */
 120   (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
 121
 122   /* Initialize input side of decompressor to consume first scan. */
 123   (*cinfo->inputctl->start_input_pass) (cinfo);
 124   /* Initialize progress monitoring. */
 125   if (cinfo->progress != NULL) {
 126     int nscans;
 127     /* Estimate number of scans to set pass_limit. */
 128     if (cinfo->progressive_mode) {
 129       /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
 130       nscans = 2 + 3 * cinfo->num_components;
 131     } else if (cinfo->inputctl->has_multiple_scans) {
 132       /* For a nonprogressive multiscan file, estimate 1 scan per component. */
 133       nscans = cinfo->num_components;
 134     } else {
 135       nscans = 1;
 136     }
 137     cinfo->progress->pass_counter = 0L;
 138     cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
 139     cinfo->progress->completed_passes = 0;
 140     cinfo->progress->total_passes = 1;
 141   }
 142 }
 143