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/* |
* jdtrans.c |
* |
* Copyright (C) 1995-1997, Thomas G. Lane. |
* This file is part of the Independent JPEG Group's software. |
* For conditions of distribution and use, see the accompanying README file. |
* |
* This file contains library routines for transcoding decompression, |
* that is, reading raw DCT coefficient arrays from an input JPEG file. |
* The routines in jdapimin.c will also be needed by a transcoder. |
*/ |
|
#define JPEG_INTERNALS |
#include "jinclude.h" |
#include "jpeglib.h" |
|
|
/* Forward declarations */ |
LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo)); |
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/* |
* Read the coefficient arrays from a JPEG file. |
* jpeg_read_header must be completed before calling this. |
* |
* The entire image is read into a set of virtual coefficient-block arrays, |
* one per component. The return value is a pointer to the array of |
* virtual-array descriptors. These can be manipulated directly via the |
* JPEG memory manager, or handed off to jpeg_write_coefficients(). |
* To release the memory occupied by the virtual arrays, call |
* jpeg_finish_decompress() when done with the data. |
* |
* An alternative usage is to simply obtain access to the coefficient arrays |
* during a buffered-image-mode decompression operation. This is allowed |
* after any jpeg_finish_output() call. The arrays can be accessed until |
* jpeg_finish_decompress() is called. (Note that any call to the library |
* may reposition the arrays, so don't rely on access_virt_barray() results |
* to stay valid across library calls.) |
* |
* Returns NULL if suspended. This case need be checked only if |
* a suspending data source is used. |
*/ |
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GLOBAL(jvirt_barray_ptr *) |
jpeg_read_coefficients (j_decompress_ptr cinfo) |
{ |
if (cinfo->global_state == DSTATE_READY) { |
/* First call: initialize active modules */ |
transdecode_master_selection(cinfo); |
cinfo->global_state = DSTATE_RDCOEFS; |
} |
if (cinfo->global_state == DSTATE_RDCOEFS) { |
/* Absorb whole file into the coef buffer */ |
for (;;) { |
int retcode; |
/* Call progress monitor hook if present */ |
if (cinfo->progress != NULL) |
(*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo); |
/* Absorb some more input */ |
retcode = (*cinfo->inputctl->consume_input) (cinfo); |
if (retcode == JPEG_SUSPENDED) |
return NULL; |
if (retcode == JPEG_REACHED_EOI) |
break; |
/* Advance progress counter if appropriate */ |
if (cinfo->progress != NULL && |
(retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) { |
if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) { |
/* startup underestimated number of scans; ratchet up one scan */ |
cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows; |
} |
} |
} |
/* Set state so that jpeg_finish_decompress does the right thing */ |
cinfo->global_state = DSTATE_STOPPING; |
} |
/* At this point we should be in state DSTATE_STOPPING if being used |
* standalone, or in state DSTATE_BUFIMAGE if being invoked to get access |
* to the coefficients during a full buffered-image-mode decompression. |
*/ |
if ((cinfo->global_state == DSTATE_STOPPING || |
cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) { |
return cinfo->coef->coef_arrays; |
} |
/* Oops, improper usage */ |
ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state); |
return NULL; /* keep compiler happy */ |
} |
|
|
/* |
* Master selection of decompression modules for transcoding. |
* This substitutes for jdmaster.c's initialization of the full decompressor. |
*/ |
|
LOCAL(void) |
transdecode_master_selection (j_decompress_ptr cinfo) |
{ |
/* This is effectively a buffered-image operation. */ |
cinfo->buffered_image = TRUE; |
|
/* Entropy decoding: either Huffman or arithmetic coding. */ |
if (cinfo->arith_code) { |
ERREXIT(cinfo, JERR_ARITH_NOTIMPL); |
} else { |
if (cinfo->progressive_mode) { |
#ifdef D_PROGRESSIVE_SUPPORTED |
jinit_phuff_decoder(cinfo); |
#else |
ERREXIT(cinfo, JERR_NOT_COMPILED); |
#endif |
} else |
jinit_huff_decoder(cinfo); |
} |
|
/* Always get a full-image coefficient buffer. */ |
jinit_d_coef_controller(cinfo, TRUE); |
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/* We can now tell the memory manager to allocate virtual arrays. */ |
(*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo); |
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/* Initialize input side of decompressor to consume first scan. */ |
(*cinfo->inputctl->start_input_pass) (cinfo); |
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/* Initialize progress monitoring. */ |
if (cinfo->progress != NULL) { |
int nscans; |
/* Estimate number of scans to set pass_limit. */ |
if (cinfo->progressive_mode) { |
/* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */ |
nscans = 2 + 3 * cinfo->num_components; |
} else if (cinfo->inputctl->has_multiple_scans) { |
/* For a nonprogressive multiscan file, estimate 1 scan per component. */ |
nscans = cinfo->num_components; |
} else { |
nscans = 1; |
} |
cinfo->progress->pass_counter = 0L; |
cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans; |
cinfo->progress->completed_passes = 0; |
cinfo->progress->total_passes = 1; |
} |
} |