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/*
* jdmaster.c
*
* Copyright (C) 1991, 1992, 1993, 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 the main control for the JPEG decompressor.
* The system-dependent (user interface) code should call jpeg_decompress()
* after doing appropriate setup of the decompress_info_struct parameter.
*/
#include "jinclude.h"
METHODDEF void
d_per_scan_method_selection (decompress_info_ptr cinfo)
/* Central point for per-scan method selection */
{
/* MCU disassembly */
jseldmcu(cinfo);
/* Upsampling of pixels */
jselupsample(cinfo);
}
LOCAL void
d_initial_method_selection (decompress_info_ptr cinfo)
/* Central point for initial method selection (after reading file header) */
{
/* JPEG file scanning method selection is already done. */
/* So is output file format selection (both are done by user interface). */
/* Gamma and color space conversion */
/* NB: this may change the component_needed flags */
jseldcolor(cinfo);
/* Color quantization selection rules */
#ifdef QUANT_1PASS_SUPPORTED
#ifdef QUANT_2PASS_SUPPORTED
/* We have both, check for conditions in which 1-pass should be used */
if (cinfo->num_components != 3 || cinfo->jpeg_color_space != CS_YCbCr)
cinfo->two_pass_quantize = FALSE; /* 2-pass only handles YCbCr input */
if (cinfo->out_color_space == CS_GRAYSCALE)
cinfo->two_pass_quantize = FALSE; /* Should use 1-pass for grayscale out */
#else /* not QUANT_2PASS_SUPPORTED */
cinfo->two_pass_quantize = FALSE; /* only have 1-pass */
#endif
#else /* not QUANT_1PASS_SUPPORTED */
#ifdef QUANT_2PASS_SUPPORTED
cinfo->two_pass_quantize = TRUE; /* only have 2-pass */
#else /* not QUANT_2PASS_SUPPORTED */
if (cinfo->quantize_colors) {
ERREXIT(cinfo->emethods, "Color quantization was not compiled");
}
#endif
#endif
#ifdef QUANT_1PASS_SUPPORTED
jsel1quantize(cinfo);
#endif
#ifdef QUANT_2PASS_SUPPORTED
jsel2quantize(cinfo);
#endif
/* Cross-block smoothing */
#ifdef BLOCK_SMOOTHING_SUPPORTED
jselbsmooth(cinfo);
#else
cinfo->do_block_smoothing = FALSE;
#endif
/* Entropy decoding: either Huffman or arithmetic coding. */
#ifdef D_ARITH_CODING_SUPPORTED
jseldarithmetic(cinfo);
#else
if (cinfo->arith_code) {
ERREXIT(cinfo->emethods, "Arithmetic coding not supported");
}
#endif
jseldhuffman(cinfo);
/* Pipeline control */
jseldpipeline(cinfo);
/* Overall control (that's me!) */
cinfo->methods->d_per_scan_method_selection = d_per_scan_method_selection;
}
LOCAL void
initial_setup (decompress_info_ptr cinfo)
/* Do computations that are needed before initial method selection */
{
short ci;
jpeg_component_info *compptr;
/* Compute maximum sampling factors; check factor validity */
cinfo->max_h_samp_factor = 1;
cinfo->max_v_samp_factor = 1;
for (ci = 0; ci < cinfo->num_components; ci++) {
compptr = &cinfo->comp_info[ci];
if (compptr->h_samp_factor<=0 || compptr->h_samp_factor>MAX_SAMP_FACTOR ||
compptr->v_samp_factor<=0 || compptr->v_samp_factor>MAX_SAMP_FACTOR)
ERREXIT(cinfo->emethods, "Bogus sampling factors");
cinfo->max_h_samp_factor = MAX(cinfo->max_h_samp_factor,
compptr->h_samp_factor);
cinfo->max_v_samp_factor = MAX(cinfo->max_v_samp_factor,
compptr->v_samp_factor);
}
/* Compute logical downsampled dimensions of components */
for (ci = 0; ci < cinfo->num_components; ci++) {
compptr = &cinfo->comp_info[ci];
compptr->true_comp_width = (cinfo->image_width * compptr->h_samp_factor
+ cinfo->max_h_samp_factor - 1)
/ cinfo->max_h_samp_factor;
compptr->true_comp_height = (cinfo->image_height * compptr->v_samp_factor
+ cinfo->max_v_samp_factor - 1)
/ cinfo->max_v_samp_factor;
}
}
/*
* This is the main entry point to the JPEG decompressor.
*/
GLOBAL void
jpeg_decompress (decompress_info_ptr cinfo)
{
/* Init pass counts to 0 --- total_passes is adjusted in method selection */
cinfo->total_passes = 0;
cinfo->completed_passes = 0;
/* Read the JPEG file header markers; everything up through the first SOS
* marker is read now. NOTE: the user interface must have initialized the
* read_file_header method pointer (eg, by calling jselrjfif or jselrtiff).
* The other file reading methods (read_scan_header etc.) were probably
* set at the same time, but could be set up by read_file_header itself.
*/
(*cinfo->methods->read_file_header) (cinfo);
if (! ((*cinfo->methods->read_scan_header) (cinfo)))
ERREXIT(cinfo->emethods, "Empty JPEG file");
/* Give UI a chance to adjust decompression parameters and select */
/* output file format based on info from file header. */
(*cinfo->methods->d_ui_method_selection) (cinfo);
/* Now select methods for decompression steps. */
initial_setup(cinfo);
d_initial_method_selection(cinfo);
/* Initialize the output file & other modules as needed */
/* (modules needing per-scan init are called by pipeline controller) */
(*cinfo->methods->output_init) (cinfo);
(*cinfo->methods->colorout_init) (cinfo);
if (cinfo->quantize_colors)
(*cinfo->methods->color_quant_init) (cinfo);
/* And let the pipeline controller do the rest. */
(*cinfo->methods->d_pipeline_controller) (cinfo);
/* Finish output file, release working storage, etc */
if (cinfo->quantize_colors)
(*cinfo->methods->color_quant_term) (cinfo);
(*cinfo->methods->colorout_term) (cinfo);
(*cinfo->methods->output_term) (cinfo);
(*cinfo->methods->read_file_trailer) (cinfo);
(*cinfo->emethods->free_all) ();
/* My, that was easy, wasn't it? */
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Netfuture.ch.