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DEFINITIONS
This source file includes following definitions.
- flush_packet
- output
- compress_init
- compress_pixel
- compress_term
- put_word
- put_3bytes
- emit_header
- METHODDEF
- METHODDEF
- METHODDEF
- GLOBAL
/*
* wrgif.c
*
* Copyright (C) 1991-1997, 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 routines to write output images in GIF format.
*
**************************************************************************
* NOTE: to avoid entanglements with Unisys' patent on LZW compression, *
* this code has been modified to output "uncompressed GIF" files. *
* There is no trace of the LZW algorithm in this file. *
**************************************************************************
*
* These routines may need modification for non-Unix environments or
* specialized applications. As they stand, they assume output to
* an ordinary stdio stream.
*/
/*
* This code is loosely based on ppmtogif from the PBMPLUS distribution
* of Feb. 1991. That file contains the following copyright notice:
* Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.
* Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.
* Copyright (C) 1989 by Jef Poskanzer.
* Permission to use, copy, modify, and distribute this software and its
* documentation for any purpose and without fee is hereby granted, provided
* that the above copyright notice appear in all copies and that both that
* copyright notice and this permission notice appear in supporting
* documentation. This software is provided "as is" without express or
* implied warranty.
*
* We are also required to state that
* "The Graphics Interchange Format(c) is the Copyright property of
* CompuServe Incorporated. GIF(sm) is a Service Mark property of
* CompuServe Incorporated."
*/
#include "cdjpeg.h" /* Common decls for cjpeg/djpeg applications */
#ifdef GIF_SUPPORTED
/* Private version of data destination object */
typedef struct {
struct djpeg_dest_struct pub; /* public fields */
j_decompress_ptr cinfo; /* back link saves passing separate parm */
/* State for packing variable-width codes into a bitstream */
int n_bits; /* current number of bits/code */
int maxcode; /* maximum code, given n_bits */
INT32 cur_accum; /* holds bits not yet output */
int cur_bits; /* # of bits in cur_accum */
/* State for GIF code assignment */
int ClearCode; /* clear code (doesn't change) */
int EOFCode; /* EOF code (ditto) */
int code_counter; /* counts output symbols */
/* GIF data packet construction buffer */
int bytesinpkt; /* # of bytes in current packet */
char packetbuf[256]; /* workspace for accumulating packet */
} gif_dest_struct;
typedef gif_dest_struct * gif_dest_ptr;
/* Largest value that will fit in N bits */
#define MAXCODE(n_bits) ((1 << (n_bits)) - 1)
/*
* Routines to package finished data bytes into GIF data blocks.
* A data block consists of a count byte (1..255) and that many data bytes.
*/
void
flush_packet (gif_dest_ptr dinfo)
/* flush any accumulated data */
{
if (dinfo->bytesinpkt > 0) { /* never write zero-length packet */
dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++;
if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt)
!= (size_t) dinfo->bytesinpkt)
ERREXIT(dinfo->cinfo, JERR_FILE_WRITE);
dinfo->bytesinpkt = 0;
}
}
/* Add a character to current packet; flush to disk if necessary */
#define CHAR_OUT(dinfo,c) \
{ (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c); \
if ((dinfo)->bytesinpkt >= 255) \
flush_packet(dinfo); \
}
/* Routine to convert variable-width codes into a byte stream */
void
output (gif_dest_ptr dinfo, int code)
/* Emit a code of n_bits bits */
/* Uses cur_accum and cur_bits to reblock into 8-bit bytes */
{
dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits;
dinfo->cur_bits += dinfo->n_bits;
while (dinfo->cur_bits >= 8) {
CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
dinfo->cur_accum >>= 8;
dinfo->cur_bits -= 8;
}
}
/* The pseudo-compression algorithm.
*
* In this module we simply output each pixel value as a separate symbol;
* thus, no compression occurs. In fact, there is expansion of one bit per
* pixel, because we use a symbol width one bit wider than the pixel width.
*
* GIF ordinarily uses variable-width symbols, and the decoder will expect
* to ratchet up the symbol width after a fixed number of symbols.
* To simplify the logic and keep the expansion penalty down, we emit a
* GIF Clear code to reset the decoder just before the width would ratchet up.
* Thus, all the symbols in the output file will have the same bit width.
* Note that emitting the Clear codes at the right times is a mere matter of
* counting output symbols and is in no way dependent on the LZW patent.
*
* With a small basic pixel width (low color count), Clear codes will be
* needed very frequently, causing the file to expand even more. So this
* simplistic approach wouldn't work too well on bilevel images, for example.
* But for output of JPEG conversions the pixel width will usually be 8 bits
* (129 to 256 colors), so the overhead added by Clear symbols is only about
* one symbol in every 256.
*/
void
compress_init (gif_dest_ptr dinfo, int i_bits)
/* Initialize pseudo-compressor */
{
/* init all the state variables */
dinfo->n_bits = i_bits;
dinfo->maxcode = MAXCODE(dinfo->n_bits);
dinfo->ClearCode = (1 << (i_bits - 1));
dinfo->EOFCode = dinfo->ClearCode + 1;
dinfo->code_counter = dinfo->ClearCode + 2;
/* init output buffering vars */
dinfo->bytesinpkt = 0;
dinfo->cur_accum = 0;
dinfo->cur_bits = 0;
/* GIF specifies an initial Clear code */
output(dinfo, dinfo->ClearCode);
}
void
compress_pixel (gif_dest_ptr dinfo, int c)
/* Accept and "compress" one pixel value.
* The given value must be less than n_bits wide.
*/
{
/* Output the given pixel value as a symbol. */
output(dinfo, c);
/* Issue Clear codes often enough to keep the reader from ratcheting up
* its symbol size.
*/
if (dinfo->code_counter < dinfo->maxcode) {
dinfo->code_counter++;
} else {
output(dinfo, dinfo->ClearCode);
dinfo->code_counter = dinfo->ClearCode + 2; /* reset the counter */
}
}
void
compress_term (gif_dest_ptr dinfo)
/* Clean up at end */
{
/* Send an EOF code */
output(dinfo, dinfo->EOFCode);
/* Flush the bit-packing buffer */
if (dinfo->cur_bits > 0) {
CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
}
/* Flush the packet buffer */
flush_packet(dinfo);
}
/* GIF header construction */
void
put_word (gif_dest_ptr dinfo, unsigned int w)
/* Emit a 16-bit word, LSB first */
{
putc(w & 0xFF, dinfo->pub.output_file);
putc((w >> 8) & 0xFF, dinfo->pub.output_file);
}
void
put_3bytes (gif_dest_ptr dinfo, int val)
/* Emit 3 copies of same byte value --- handy subr for colormap construction */
{
putc(val, dinfo->pub.output_file);
putc(val, dinfo->pub.output_file);
putc(val, dinfo->pub.output_file);
}
void
emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)
/* Output the GIF file header, including color map */
/* If colormap==NULL, synthesize a gray-scale colormap */
{
int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;
int cshift = dinfo->cinfo->data_precision - 8;
int i;
if (num_colors > 256)
ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);
/* Compute bits/pixel and related values */
BitsPerPixel = 1;
while (num_colors > (1 << BitsPerPixel))
BitsPerPixel++;
ColorMapSize = 1 << BitsPerPixel;
if (BitsPerPixel <= 1)
InitCodeSize = 2;
else
InitCodeSize = BitsPerPixel;
/*
* Write the GIF header.
* Note that we generate a plain GIF87 header for maximum compatibility.
*/
putc('G', dinfo->pub.output_file);
putc('I', dinfo->pub.output_file);
putc('F', dinfo->pub.output_file);
putc('8', dinfo->pub.output_file);
putc('7', dinfo->pub.output_file);
putc('a', dinfo->pub.output_file);
/* Write the Logical Screen Descriptor */
put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);
put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
FlagByte = 0x80; /* Yes, there is a global color table */
FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */
FlagByte |= (BitsPerPixel-1); /* size of global color table */
putc(FlagByte, dinfo->pub.output_file);
putc(0, dinfo->pub.output_file); /* Background color index */
putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */
/* Write the Global Color Map */
/* If the color map is more than 8 bits precision, */
/* we reduce it to 8 bits by shifting */
for (i=0; i < ColorMapSize; i++) {
if (i < num_colors) {
if (colormap != NULL) {
if (dinfo->cinfo->out_color_space == JCS_RGB) {
/* Normal case: RGB color map */
putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);
putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);
putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);
} else {
/* Grayscale "color map": possible if quantizing grayscale image */
put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);
}
} else {
/* Create a gray-scale map of num_colors values, range 0..255 */
put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));
}
} else {
/* fill out the map to a power of 2 */
put_3bytes(dinfo, 0);
}
}
/* Write image separator and Image Descriptor */
putc(',', dinfo->pub.output_file); /* separator */
put_word(dinfo, 0); /* left/top offset */
put_word(dinfo, 0);
put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */
put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
/* flag byte: not interlaced, no local color map */
putc(0x00, dinfo->pub.output_file);
/* Write Initial Code Size byte */
putc(InitCodeSize, dinfo->pub.output_file);
/* Initialize for "compression" of image data */
compress_init(dinfo, InitCodeSize+1);
}
/*
* Startup: write the file header.
*/
METHODDEF(void)
start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
{
gif_dest_ptr dest = (gif_dest_ptr) dinfo;
if (cinfo->quantize_colors)
emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);
else
emit_header(dest, 256, (JSAMPARRAY) NULL);
}
/*
* Write some pixel data.
* In this module rows_supplied will always be 1.
*/
METHODDEF(void)
put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo,
JDIMENSION rows_supplied)
{
gif_dest_ptr dest = (gif_dest_ptr) dinfo;
register JSAMPROW ptr;
register JDIMENSION col;
ptr = dest->pub.buffer[0];
for (col = cinfo->output_width; col > 0; col--) {
compress_pixel(dest, GETJSAMPLE(*ptr++));
}
}
/*
* Finish up at the end of the file.
*/
METHODDEF(void)
finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
{
gif_dest_ptr dest = (gif_dest_ptr) dinfo;
/* Flush "compression" mechanism */
compress_term(dest);
/* Write a zero-length data block to end the series */
putc(0, dest->pub.output_file);
/* Write the GIF terminator mark */
putc(';', dest->pub.output_file);
/* Make sure we wrote the output file OK */
fflush(dest->pub.output_file);
if (ferror(dest->pub.output_file))
ERREXIT(cinfo, JERR_FILE_WRITE);
}
/*
* The module selection routine for GIF format output.
*/
GLOBAL(djpeg_dest_ptr)
jinit_write_gif (j_decompress_ptr cinfo)
{
gif_dest_ptr dest;
/* Create module interface object, fill in method pointers */
dest = (gif_dest_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(gif_dest_struct));
dest->cinfo = cinfo; /* make back link for subroutines */
dest->pub.start_output = start_output_gif;
dest->pub.put_pixel_rows = put_pixel_rows;
dest->pub.finish_output = finish_output_gif;
if (cinfo->out_color_space != JCS_GRAYSCALE &&
cinfo->out_color_space != JCS_RGB)
ERREXIT(cinfo, JERR_GIF_COLORSPACE);
/* Force quantization if color or if > 8 bits input */
if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) {
/* Force quantization to at most 256 colors */
cinfo->quantize_colors = TRUE;
if (cinfo->desired_number_of_colors > 256)
cinfo->desired_number_of_colors = 256;
}
/* Calculate output image dimensions so we can allocate space */
jpeg_calc_output_dimensions(cinfo);
if (cinfo->output_components != 1) /* safety check: just one component? */
ERREXIT(cinfo, JERR_GIF_BUG);
/* Create decompressor output buffer. */
dest->pub.buffer = (*cinfo->mem->alloc_sarray)
((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1);
dest->pub.buffer_height = 1;
return (djpeg_dest_ptr) dest;
}
#endif /* GIF_SUPPORTED */