Doxygen Source Code Documentation
jdtrans.c
Go to the documentation of this file.00001 /* 00002 * jdtrans.c 00003 * 00004 * Copyright (C) 1995-1997, Thomas G. Lane. 00005 * This file is part of the Independent JPEG Group's software. 00006 * For conditions of distribution and use, see the accompanying README file. 00007 * 00008 * This file contains library routines for transcoding decompression, 00009 * that is, reading raw DCT coefficient arrays from an input JPEG file. 00010 * The routines in jdapimin.c will also be needed by a transcoder. 00011 */ 00012 00013 #define JPEG_INTERNALS 00014 #include "jinclude.h" 00015 #include "jpeglib.h" 00016 00017 00018 /* Forward declarations */ 00019 LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo)); 00020 00021 00022 /* 00023 * Read the coefficient arrays from a JPEG file. 00024 * jpeg_read_header must be completed before calling this. 00025 * 00026 * The entire image is read into a set of virtual coefficient-block arrays, 00027 * one per component. The return value is a pointer to the array of 00028 * virtual-array descriptors. These can be manipulated directly via the 00029 * JPEG memory manager, or handed off to jpeg_write_coefficients(). 00030 * To release the memory occupied by the virtual arrays, call 00031 * jpeg_finish_decompress() when done with the data. 00032 * 00033 * An alternative usage is to simply obtain access to the coefficient arrays 00034 * during a buffered-image-mode decompression operation. This is allowed 00035 * after any jpeg_finish_output() call. The arrays can be accessed until 00036 * jpeg_finish_decompress() is called. (Note that any call to the library 00037 * may reposition the arrays, so don't rely on access_virt_barray() results 00038 * to stay valid across library calls.) 00039 * 00040 * Returns NULL if suspended. This case need be checked only if 00041 * a suspending data source is used. 00042 */ 00043 00044 GLOBAL(jvirt_barray_ptr *) 00045 jpeg_read_coefficients (j_decompress_ptr cinfo) 00046 { 00047 if (cinfo->global_state == DSTATE_READY) { 00048 /* First call: initialize active modules */ 00049 transdecode_master_selection(cinfo); 00050 cinfo->global_state = DSTATE_RDCOEFS; 00051 } 00052 if (cinfo->global_state == DSTATE_RDCOEFS) { 00053 /* Absorb whole file into the coef buffer */ 00054 for (;;) { 00055 int retcode; 00056 /* Call progress monitor hook if present */ 00057 if (cinfo->progress != NULL) 00058 (*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo); 00059 /* Absorb some more input */ 00060 retcode = (*cinfo->inputctl->consume_input) (cinfo); 00061 if (retcode == JPEG_SUSPENDED) 00062 return NULL; 00063 if (retcode == JPEG_REACHED_EOI) 00064 break; 00065 /* Advance progress counter if appropriate */ 00066 if (cinfo->progress != NULL && 00067 (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) { 00068 if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) { 00069 /* startup underestimated number of scans; ratchet up one scan */ 00070 cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows; 00071 } 00072 } 00073 } 00074 /* Set state so that jpeg_finish_decompress does the right thing */ 00075 cinfo->global_state = DSTATE_STOPPING; 00076 } 00077 /* At this point we should be in state DSTATE_STOPPING if being used 00078 * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access 00079 * to the coefficients during a full buffered-image-mode decompression. 00080 */ 00081 if ((cinfo->global_state == DSTATE_STOPPING || 00082 cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) { 00083 return cinfo->coef->coef_arrays; 00084 } 00085 /* Oops, improper usage */ 00086 ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state); 00087 return NULL; /* keep compiler happy */ 00088 } 00089 00090 00091 /* 00092 * Master selection of decompression modules for transcoding. 00093 * This substitutes for jdmaster.c's initialization of the full decompressor. 00094 */ 00095 00096 LOCAL(void) 00097 transdecode_master_selection (j_decompress_ptr cinfo) 00098 { 00099 /* This is effectively a buffered-image operation. */ 00100 cinfo->buffered_image = TRUE; 00101 00102 /* Entropy decoding: either Huffman or arithmetic coding. */ 00103 if (cinfo->arith_code) { 00104 ERREXIT(cinfo, JERR_ARITH_NOTIMPL); 00105 } else { 00106 if (cinfo->progressive_mode) { 00107 #ifdef D_PROGRESSIVE_SUPPORTED 00108 jinit_phuff_decoder(cinfo); 00109 #else 00110 ERREXIT(cinfo, JERR_NOT_COMPILED); 00111 #endif 00112 } else 00113 jinit_huff_decoder(cinfo); 00114 } 00115 00116 /* Always get a full-image coefficient buffer. */ 00117 jinit_d_coef_controller(cinfo, TRUE); 00118 00119 /* We can now tell the memory manager to allocate virtual arrays. */ 00120 (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo); 00121 00122 /* Initialize input side of decompressor to consume first scan. */ 00123 (*cinfo->inputctl->start_input_pass) (cinfo); 00124 00125 /* Initialize progress monitoring. */ 00126 if (cinfo->progress != NULL) { 00127 int nscans; 00128 /* Estimate number of scans to set pass_limit. */ 00129 if (cinfo->progressive_mode) { 00130 /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */ 00131 nscans = 2 + 3 * cinfo->num_components; 00132 } else if (cinfo->inputctl->has_multiple_scans) { 00133 /* For a nonprogressive multiscan file, estimate 1 scan per component. */ 00134 nscans = cinfo->num_components; 00135 } else { 00136 nscans = 1; 00137 } 00138 cinfo->progress->pass_counter = 0L; 00139 cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans; 00140 cinfo->progress->completed_passes = 0; 00141 cinfo->progress->total_passes = 1; 00142 } 00143 }