jdtrans.c

00001 /*
00002  * jdtrans.c
00003  *
00004  * Copyright (C) 1995-1997, Thomas G. Lane.
00005  * Modified 2000-2009 by Guido Vollbeding.
00006  * This file is part of the Independent JPEG Group's software.
00007  * For conditions of distribution and use, see the accompanying README file.
00008  *
00009  * This file contains library routines for transcoding decompression,
00010  * that is, reading raw DCT coefficient arrays from an input JPEG file.
00011  * The routines in jdapimin.c will also be needed by a transcoder.
00012  */
00013 
00014 #define JPEG_INTERNALS
00015 #include "jinclude.h"
00016 #include "jpeglib.h"
00017 
00018 
00019 /* Forward declarations */
00020 LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo));
00021 
00022 
00023 /*
00024  * Read the coefficient arrays from a JPEG file.
00025  * jpeg_read_header must be completed before calling this.
00026  *
00027  * The entire image is read into a set of virtual coefficient-block arrays,
00028  * one per component.  The return value is a pointer to the array of
00029  * virtual-array descriptors.  These can be manipulated directly via the
00030  * JPEG memory manager, or handed off to jpeg_write_coefficients().
00031  * To release the memory occupied by the virtual arrays, call
00032  * jpeg_finish_decompress() when done with the data.
00033  *
00034  * An alternative usage is to simply obtain access to the coefficient arrays
00035  * during a buffered-image-mode decompression operation.  This is allowed
00036  * after any jpeg_finish_output() call.  The arrays can be accessed until
00037  * jpeg_finish_decompress() is called.  (Note that any call to the library
00038  * may reposition the arrays, so don't rely on access_virt_barray() results
00039  * to stay valid across library calls.)
00040  *
00041  * Returns NULL if suspended.  This case need be checked only if
00042  * a suspending data source is used.
00043  */
00044 
00045 GLOBAL(jvirt_barray_ptr *)
00046 jpeg_read_coefficients (j_decompress_ptr cinfo)
00047 {
00048   if (cinfo->global_state == DSTATE_READY) {
00049     /* First call: initialize active modules */
00050     transdecode_master_selection(cinfo);
00051     cinfo->global_state = DSTATE_RDCOEFS;
00052   }
00053   if (cinfo->global_state == DSTATE_RDCOEFS) {
00054     /* Absorb whole file into the coef buffer */
00055     for (;;) {
00056       int retcode;
00057       /* Call progress monitor hook if present */
00058       if (cinfo->progress != NULL)
00059     (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
00060       /* Absorb some more input */
00061       retcode = (*cinfo->inputctl->consume_input) (cinfo);
00062       if (retcode == JPEG_SUSPENDED)
00063     return NULL;
00064       if (retcode == JPEG_REACHED_EOI)
00065     break;
00066       /* Advance progress counter if appropriate */
00067       if (cinfo->progress != NULL &&
00068       (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
00069     if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
00070       /* startup underestimated number of scans; ratchet up one scan */
00071       cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
00072     }
00073       }
00074     }
00075     /* Set state so that jpeg_finish_decompress does the right thing */
00076     cinfo->global_state = DSTATE_STOPPING;
00077   }
00078   /* At this point we should be in state DSTATE_STOPPING if being used
00079    * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access
00080    * to the coefficients during a full buffered-image-mode decompression.
00081    */
00082   if ((cinfo->global_state == DSTATE_STOPPING ||
00083        cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) {
00084     return cinfo->coef->coef_arrays;
00085   }
00086   /* Oops, improper usage */
00087   ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
00088   return NULL;          /* keep compiler happy */
00089 }
00090 
00091 
00092 /*
00093  * Master selection of decompression modules for transcoding.
00094  * This substitutes for jdmaster.c's initialization of the full decompressor.
00095  */
00096 
00097 LOCAL(void)
00098 transdecode_master_selection (j_decompress_ptr cinfo)
00099 {
00100   /* This is effectively a buffered-image operation. */
00101   cinfo->buffered_image = TRUE;
00102 
00103   /* Compute output image dimensions and related values. */
00104   jpeg_core_output_dimensions(cinfo);
00105 
00106   /* Entropy decoding: either Huffman or arithmetic coding. */
00107   if (cinfo->arith_code)
00108     jinit_arith_decoder(cinfo);
00109   else {
00110     jinit_huff_decoder(cinfo);
00111   }
00112 
00113   /* Always get a full-image coefficient buffer. */
00114   jinit_d_coef_controller(cinfo, TRUE);
00115 
00116   /* We can now tell the memory manager to allocate virtual arrays. */
00117   (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
00118 
00119   /* Initialize input side of decompressor to consume first scan. */
00120   (*cinfo->inputctl->start_input_pass) (cinfo);
00121 
00122   /* Initialize progress monitoring. */
00123   if (cinfo->progress != NULL) {
00124     int nscans;
00125     /* Estimate number of scans to set pass_limit. */
00126     if (cinfo->progressive_mode) {
00127       /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
00128       nscans = 2 + 3 * cinfo->num_components;
00129     } else if (cinfo->inputctl->has_multiple_scans) {
00130       /* For a nonprogressive multiscan file, estimate 1 scan per component. */
00131       nscans = cinfo->num_components;
00132     } else {
00133       nscans = 1;
00134     }
00135     cinfo->progress->pass_counter = 0L;
00136     cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
00137     cinfo->progress->completed_passes = 0;
00138     cinfo->progress->total_passes = 1;
00139   }
00140 }