Category : C Source Code
Archive   : JPSRC2.ZIP
Filename : JDDEFLTS.C
* jddeflts.c
*
* Copyright (C) 1991, 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 optional default-setting code for the JPEG decompressor.
* User interfaces do not have to use this file, but those that don't use it
* must know more about the innards of the JPEG code.
*/
#include "jinclude.h"
/*
* Reload the input buffer after it's been emptied, and return the next byte.
* See the JGETC macro for calling conditions.
*
* This routine is used only if the system-dependent user interface passes
* standard_buffering = TRUE to j_d_defaults. Otherwise, the UI must supply
* a corresponding routine. Note that in any case, this routine is likely
* to be used only for JFIF or similar serial-access JPEG file formats.
* The input file control module for a random-access format such as TIFF/JPEG
* would need to override the read_jpeg_data method with its own routine.
*
* This routine would need to be replaced if reading JPEG data from something
* other than a stdio stream.
*/
METHODDEF int
read_jpeg_data (decompress_info_ptr cinfo)
{
cinfo->next_input_byte = cinfo->input_buffer + MIN_UNGET;
cinfo->bytes_in_buffer = (int) FREAD(cinfo->input_file,
cinfo->next_input_byte,
JPEG_BUF_SIZE);
if (cinfo->bytes_in_buffer <= 0)
ERREXIT(cinfo->emethods, "Unexpected EOF in JPEG file");
return JGETC(cinfo);
}
/* Default parameter setup for decompression.
*
* User interfaces that don't choose to use this routine must do their
* own setup of all these parameters. Alternately, you can call this
* to establish defaults and then alter parameters selectively. This
* is the recommended approach since, if we add any new parameters,
* your code will still work (they'll be set to reasonable defaults).
*
* standard_buffering should be TRUE if the JPEG data is to come from
* a stdio stream and the user interface isn't interested in changing
* the normal input-buffering logic. If FALSE is passed, the user
* interface must provide its own read_jpeg_data method and must
* set up its own input buffer. (Alternately, you can pass TRUE to
* let the buffer be allocated here, then override read_jpeg_data with
* your own routine.)
*/
GLOBAL void
j_d_defaults (decompress_info_ptr cinfo, boolean standard_buffering)
/* NB: the external methods must already be set up. */
{
/* Default to RGB output */
/* UI can override by changing out_color_space */
cinfo->out_color_space = CS_RGB;
cinfo->jpeg_color_space = CS_UNKNOWN;
/* Setting any other value in jpeg_color_space overrides heuristics in */
/* jrdjfif.c. That might be useful when reading non-JFIF JPEG files, */
/* but ordinarily the UI shouldn't change it. */
/* Default to no gamma correction of output */
cinfo->output_gamma = 1.0;
/* Default to no color quantization */
cinfo->quantize_colors = FALSE;
/* but set reasonable default parameters for quantization, */
/* so that turning on quantize_colors is sufficient to do something useful */
cinfo->two_pass_quantize = FALSE; /* may change to TRUE later */
cinfo->use_dithering = TRUE;
cinfo->desired_number_of_colors = 256;
/* Default to no smoothing */
cinfo->do_block_smoothing = FALSE;
cinfo->do_pixel_smoothing = FALSE;
if (standard_buffering) {
/* Allocate memory for input buffer. */
cinfo->input_buffer = (char *) (*cinfo->emethods->alloc_small)
((size_t) (JPEG_BUF_SIZE + MIN_UNGET));
cinfo->bytes_in_buffer = 0; /* initialize buffer to empty */
/* Install standard buffer-reloading method. */
cinfo->methods->read_jpeg_data = read_jpeg_data;
}
}
/* This routine releases storage allocated by j_d_defaults.
* Note that freeing the method pointer structs and the decompress_info_struct
* itself are the responsibility of the user interface.
*
* standard_buffering must agree with what was passed to j_d_defaults.
*/
GLOBAL void
j_d_free_defaults (decompress_info_ptr cinfo, boolean standard_buffering)
{
if (standard_buffering) {
(*cinfo->emethods->free_small) ((void *) cinfo->input_buffer);
}
}
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