blob: b8f12297314e4a33322c12263b3e2849addacc15 [file] [log] [blame]
* jddeflts.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 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"
/* Default do-nothing progress monitoring routine.
* This can be overridden by a user interface that wishes to
* provide progress monitoring; just set methods->progress_monitor
* after j_d_defaults is done. The routine will be called periodically
* during the decompression process.
* During any one pass, loopcounter increases from 0 up to (not including)
* looplimit; the step size is not necessarily 1. Both the step size and
* the limit may differ between passes. The expected total number of passes
* is in cinfo->total_passes, and the number of passes already completed is
* in cinfo->completed_passes. Thus the fraction of work completed may be
* estimated as
* completed_passes + (loopcounter/looplimit)
* ------------------------------------------
* total_passes
* ignoring the fact that the passes may not be equal amounts of work.
* When decompressing, the total_passes figure is an estimate that may be
* on the high side; completed_passes will jump by more than one if some
* passes are skipped.
progress_monitor (decompress_info_ptr cinfo, long loopcounter, long looplimit)
/* do nothing */
/* Default comment-block processing routine.
* This can be overridden by an application that wishes to examine
* COM blocks found in the JPEG file. The default routine does nothing.
* CAUTION: the comment processing routine MUST call JGETC() exactly
* comment_length times to read the comment data, whether it intends
* to do anything with the data or not!
* Keep in mind that (a) there may be more than one COM block in a file;
* (b) there's no guarantee that what's in the block is ASCII data.
process_comment (decompress_info_ptr cinfo, long comment_length)
while (comment_length-- > 0) {
(void) JGETC(cinfo);
* Reload the input buffer after it's been emptied, and return the next byte.
* See the JGETC macro for calling conditions. Note in particular that
* read_jpeg_data may NOT return EOF. If no more data is available, it must
* exit via ERREXIT, or perhaps synthesize fake data (such as an RST marker).
* In the present implementation, we insert an EOI marker; this might not be
* appropriate for non-JFIF file formats, but it usually allows us to handle
* a truncated JFIF file.
* This routine can be overridden by the system-dependent user interface,
* in case the data source is not a stdio stream or some other special
* condition applies. Note, however, that this capability only applies for
* JFIF or similar serial-access JPEG file formats. The input file control
* module for a random-access format such as TIFF/JPEG would most likely
* override the read_jpeg_data method with its own routine.
read_jpeg_data (decompress_info_ptr cinfo)
cinfo->next_input_byte = cinfo->input_buffer + MIN_UNGET;
cinfo->bytes_in_buffer = (int) JFREAD(cinfo->input_file,
if (cinfo->bytes_in_buffer <= 0) {
WARNMS(cinfo->emethods, "Premature EOF in JPEG file");
cinfo->next_input_byte[0] = (char) 0xFF;
cinfo->next_input_byte[1] = (char) 0xD9; /* EOI marker */
cinfo->bytes_in_buffer = 2;
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 to cause an input buffer to be allocated
* (the normal case); if FALSE, the user interface must provide a buffer.
* This option is most useful in the case that the buffer must not be freed
* at the end of an image. (For example, when reading a sequence of images
* from a single file, the remaining data in the buffer represents the
* start of the next image and mustn't be discarded.) To handle this,
* allocate the input buffer yourself at startup, WITHOUT using alloc_small
* (probably a direct call to malloc() instead). Then pass FALSE on each
* call to j_d_defaults to ensure the buffer state is not modified.
* If the source of the JPEG data is not a stdio stream, override the
* read_jpeg_data method with your own routine after calling j_d_defaults.
* You can still use the standard buffer if it's appropriate.
* CAUTION: if you want to decompress multiple images per run, it's necessary
* to call j_d_defaults before *each* call to jpeg_decompress, since subsidiary
* structures like the quantization tables are automatically freed during
* cleanup.
j_d_defaults (decompress_info_ptr cinfo, boolean standard_buffering)
/* NB: the external methods must already be set up. */
short i;
/* Initialize pointers as needed to mark stuff unallocated. */
/* Outer application may fill in default tables for abbreviated files... */
cinfo->comp_info = NULL;
for (i = 0; i < NUM_QUANT_TBLS; i++)
cinfo->quant_tbl_ptrs[i] = NULL;
for (i = 0; i < NUM_HUFF_TBLS; i++) {
cinfo->dc_huff_tbl_ptrs[i] = NULL;
cinfo->ac_huff_tbl_ptrs[i] = NULL;
cinfo->colormap = NULL;
/* 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 = TRUE;
cinfo->use_dithering = TRUE;
cinfo->desired_number_of_colors = 256;
/* Default to no smoothing */
cinfo->do_block_smoothing = FALSE;
cinfo->do_pixel_smoothing = FALSE;
/* Allocate memory for input buffer, unless outer application provides it. */
if (standard_buffering) {
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 (outer code may override). */
cinfo->methods->read_jpeg_data = read_jpeg_data;
/* Install default do-nothing progress monitoring method. */
cinfo->methods->progress_monitor = progress_monitor;
/* Install default comment-block processing method. */
cinfo->methods->process_comment = process_comment;