The Independent JPEG Group's JPEG software v5
This commit is contained in:
Thomas G. Lane
DRC
500
wrgif.c
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500
wrgif.c
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/*
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* wrgif.c
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*
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* Copyright (C) 1991-1994, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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*
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* This file contains routines to write output images in GIF format.
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*
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* These routines may need modification for non-Unix environments or
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* specialized applications. As they stand, they assume output to
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* an ordinary stdio stream.
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*/
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/*
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* This code is loosely based on ppmtogif from the PBMPLUS distribution
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* of Feb. 1991. That file contains the following copyright notice:
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* Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.
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* Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.
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* Copyright (C) 1989 by Jef Poskanzer.
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* Permission to use, copy, modify, and distribute this software and its
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* documentation for any purpose and without fee is hereby granted, provided
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* that the above copyright notice appear in all copies and that both that
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* copyright notice and this permission notice appear in supporting
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* documentation. This software is provided "as is" without express or
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* implied warranty.
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*
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* We are also required to state that
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* "The Graphics Interchange Format(c) is the Copyright property of
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* CompuServe Incorporated. GIF(sm) is a Service Mark property of
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* CompuServe Incorporated."
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*/
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#include "cdjpeg.h" /* Common decls for cjpeg/djpeg applications */
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#ifdef GIF_SUPPORTED
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#define MAX_LZW_BITS 12 /* maximum LZW code size (4096 symbols) */
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typedef INT16 code_int; /* must hold -1 .. 2**MAX_LZW_BITS */
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#define LZW_TABLE_SIZE ((code_int) 1 << MAX_LZW_BITS)
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#define HSIZE 5003 /* hash table size for 80% occupancy */
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typedef int hash_int; /* must hold -2*HSIZE..2*HSIZE */
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#define MAXCODE(n_bits) (((code_int) 1 << (n_bits)) - 1)
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/*
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* The LZW hash table consists of two parallel arrays:
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* hash_code[i] code of symbol in slot i, or 0 if empty slot
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* hash_value[i] symbol's value; undefined if empty slot
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* where slot values (i) range from 0 to HSIZE-1. The symbol value is
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* its prefix symbol's code concatenated with its suffix character.
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*
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* Algorithm: use open addressing double hashing (no chaining) on the
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* prefix code / suffix character combination. We do a variant of Knuth's
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* algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
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* secondary probe.
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*
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* The hash_value[] table is allocated from FAR heap space since it would
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* use up rather a lot of the near data space in a PC.
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*/
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typedef INT32 hash_entry; /* must hold (code_int<<8) | byte */
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#define HASH_ENTRY(prefix,suffix) ((((hash_entry) (prefix)) << 8) | (suffix))
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/* Private version of data destination object */
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typedef struct {
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struct djpeg_dest_struct pub; /* public fields */
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j_decompress_ptr cinfo; /* back link saves passing separate parm */
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/* State for packing variable-width codes into a bitstream */
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int n_bits; /* current number of bits/code */
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code_int maxcode; /* maximum code, given n_bits */
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int init_bits; /* initial n_bits ... restored after clear */
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INT32 cur_accum; /* holds bits not yet output */
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int cur_bits; /* # of bits in cur_accum */
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/* LZW string construction */
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code_int waiting_code; /* symbol not yet output; may be extendable */
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boolean first_byte; /* if TRUE, waiting_code is not valid */
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/* State for LZW code assignment */
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code_int ClearCode; /* clear code (doesn't change) */
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code_int EOFCode; /* EOF code (ditto) */
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code_int free_code; /* first not-yet-used symbol code */
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/* LZW hash table */
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code_int *hash_code; /* => hash table of symbol codes */
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hash_entry FAR *hash_value; /* => hash table of symbol values */
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/* GIF data packet construction buffer */
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int bytesinpkt; /* # of bytes in current packet */
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char packetbuf[256]; /* workspace for accumulating packet */
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} gif_dest_struct;
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typedef gif_dest_struct * gif_dest_ptr;
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/*
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* Routines to package compressed data bytes into GIF data blocks.
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* A data block consists of a count byte (1..255) and that many data bytes.
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*/
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LOCAL void
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flush_packet (gif_dest_ptr dinfo)
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/* flush any accumulated data */
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{
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if (dinfo->bytesinpkt > 0) { /* never write zero-length packet */
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dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++;
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if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt)
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!= (size_t) dinfo->bytesinpkt)
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ERREXIT(dinfo->cinfo, JERR_FILE_WRITE);
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dinfo->bytesinpkt = 0;
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}
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}
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/* Add a character to current packet; flush to disk if necessary */
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#define CHAR_OUT(dinfo,c) \
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{ (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c); \
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if ((dinfo)->bytesinpkt >= 255) \
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flush_packet(dinfo); \
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}
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/* Routine to convert variable-width codes into a byte stream */
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LOCAL void
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output (gif_dest_ptr dinfo, code_int code)
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/* Emit a code of n_bits bits */
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/* Uses cur_accum and cur_bits to reblock into 8-bit bytes */
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{
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dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits;
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dinfo->cur_bits += dinfo->n_bits;
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while (dinfo->cur_bits >= 8) {
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CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
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dinfo->cur_accum >>= 8;
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dinfo->cur_bits -= 8;
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}
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/*
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* If the next entry is going to be too big for the code size,
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* then increase it, if possible. We do this here to ensure
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* that it's done in sync with the decoder's codesize increases.
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*/
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if (dinfo->free_code > dinfo->maxcode) {
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dinfo->n_bits++;
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if (dinfo->n_bits == MAX_LZW_BITS)
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dinfo->maxcode = LZW_TABLE_SIZE; /* free_code will never exceed this */
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else
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dinfo->maxcode = MAXCODE(dinfo->n_bits);
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}
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}
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/* The LZW algorithm proper */
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LOCAL void
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clear_hash (gif_dest_ptr dinfo)
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/* Fill the hash table with empty entries */
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{
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/* It's sufficient to zero hash_code[] */
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MEMZERO(dinfo->hash_code, HSIZE * SIZEOF(code_int));
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}
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LOCAL void
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clear_block (gif_dest_ptr dinfo)
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/* Reset compressor and issue a Clear code */
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{
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clear_hash(dinfo); /* delete all the symbols */
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dinfo->free_code = dinfo->ClearCode + 2;
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output(dinfo, dinfo->ClearCode); /* inform decoder */
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dinfo->n_bits = dinfo->init_bits; /* reset code size */
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dinfo->maxcode = MAXCODE(dinfo->n_bits);
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}
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LOCAL void
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compress_init (gif_dest_ptr dinfo, int i_bits)
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/* Initialize LZW compressor */
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{
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/* init all the state variables */
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dinfo->n_bits = dinfo->init_bits = i_bits;
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dinfo->maxcode = MAXCODE(dinfo->n_bits);
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dinfo->ClearCode = ((code_int) 1 << (i_bits - 1));
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dinfo->EOFCode = dinfo->ClearCode + 1;
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dinfo->free_code = dinfo->ClearCode + 2;
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dinfo->first_byte = TRUE; /* no waiting symbol yet */
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/* init output buffering vars */
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dinfo->bytesinpkt = 0;
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dinfo->cur_accum = 0;
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dinfo->cur_bits = 0;
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/* clear hash table */
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clear_hash(dinfo);
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/* GIF specifies an initial Clear code */
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output(dinfo, dinfo->ClearCode);
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}
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LOCAL void
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compress_byte (gif_dest_ptr dinfo, int c)
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/* Accept and compress one 8-bit byte */
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{
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register hash_int i;
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register hash_int disp;
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register hash_entry probe_value;
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if (dinfo->first_byte) { /* need to initialize waiting_code */
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dinfo->waiting_code = c;
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dinfo->first_byte = FALSE;
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return;
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}
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/* Probe hash table to see if a symbol exists for
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* waiting_code followed by c.
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* If so, replace waiting_code by that symbol and return.
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*/
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i = ((hash_int) c << (MAX_LZW_BITS-8)) + dinfo->waiting_code;
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/* i is less than twice 2**MAX_LZW_BITS, therefore less than twice HSIZE */
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if (i >= HSIZE)
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i -= HSIZE;
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probe_value = HASH_ENTRY(dinfo->waiting_code, c);
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if (dinfo->hash_code[i] != 0) { /* is first probed slot empty? */
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if (dinfo->hash_value[i] == probe_value) {
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dinfo->waiting_code = dinfo->hash_code[i];
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return;
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}
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if (i == 0) /* secondary hash (after G. Knott) */
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disp = 1;
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else
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disp = HSIZE - i;
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for (;;) {
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i -= disp;
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if (i < 0)
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i += HSIZE;
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if (dinfo->hash_code[i] == 0)
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break; /* hit empty slot */
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if (dinfo->hash_value[i] == probe_value) {
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dinfo->waiting_code = dinfo->hash_code[i];
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return;
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}
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}
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}
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/* here when hashtable[i] is an empty slot; desired symbol not in table */
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output(dinfo, dinfo->waiting_code);
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if (dinfo->free_code < LZW_TABLE_SIZE) {
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dinfo->hash_code[i] = dinfo->free_code++; /* add symbol to hashtable */
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dinfo->hash_value[i] = probe_value;
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} else
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clear_block(dinfo);
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dinfo->waiting_code = c;
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}
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LOCAL void
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compress_term (gif_dest_ptr dinfo)
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/* Clean up at end */
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{
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/* Flush out the buffered code */
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if (! dinfo->first_byte)
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output(dinfo, dinfo->waiting_code);
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/* Send an EOF code */
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output(dinfo, dinfo->EOFCode);
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/* Flush the bit-packing buffer */
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if (dinfo->cur_bits > 0) {
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CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
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}
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/* Flush the packet buffer */
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flush_packet(dinfo);
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}
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/* GIF header construction */
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LOCAL void
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put_word (gif_dest_ptr dinfo, unsigned int w)
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/* Emit a 16-bit word, LSB first */
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{
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putc(w & 0xFF, dinfo->pub.output_file);
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putc((w >> 8) & 0xFF, dinfo->pub.output_file);
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}
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LOCAL void
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put_3bytes (gif_dest_ptr dinfo, int val)
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/* Emit 3 copies of same byte value --- handy subr for colormap construction */
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{
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putc(val, dinfo->pub.output_file);
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putc(val, dinfo->pub.output_file);
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putc(val, dinfo->pub.output_file);
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}
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LOCAL void
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emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)
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/* Output the GIF file header, including color map */
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/* If colormap==NULL, synthesize a gray-scale colormap */
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{
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int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;
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int cshift = dinfo->cinfo->data_precision - 8;
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int i;
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if (num_colors > 256)
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ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);
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/* Compute bits/pixel and related values */
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BitsPerPixel = 1;
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while (num_colors > (1 << BitsPerPixel))
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BitsPerPixel++;
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ColorMapSize = 1 << BitsPerPixel;
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if (BitsPerPixel <= 1)
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InitCodeSize = 2;
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else
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InitCodeSize = BitsPerPixel;
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/*
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* Write the GIF header.
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* Note that we generate a plain GIF87 header for maximum compatibility.
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*/
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putc('G', dinfo->pub.output_file);
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putc('I', dinfo->pub.output_file);
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putc('F', dinfo->pub.output_file);
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putc('8', dinfo->pub.output_file);
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putc('7', dinfo->pub.output_file);
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putc('a', dinfo->pub.output_file);
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/* Write the Logical Screen Descriptor */
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
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FlagByte = 0x80; /* Yes, there is a global color table */
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FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */
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FlagByte |= (BitsPerPixel-1); /* size of global color table */
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putc(FlagByte, dinfo->pub.output_file);
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putc(0, dinfo->pub.output_file); /* Background color index */
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putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */
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/* Write the Global Color Map */
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/* If the color map is more than 8 bits precision, */
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/* we reduce it to 8 bits by shifting */
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for (i=0; i < ColorMapSize; i++) {
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if (i < num_colors) {
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if (colormap != NULL) {
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if (dinfo->cinfo->out_color_space == JCS_RGB) {
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/* Normal case: RGB color map */
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putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);
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putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);
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putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);
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} else {
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/* Grayscale "color map": possible if quantizing grayscale image */
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put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);
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}
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} else {
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/* Create a gray-scale map of num_colors values, range 0..255 */
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put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));
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}
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} else {
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/* fill out the map to a power of 2 */
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put_3bytes(dinfo, 0);
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}
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}
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/* Write image separator and Image Descriptor */
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putc(',', dinfo->pub.output_file); /* separator */
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put_word(dinfo, 0); /* left/top offset */
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put_word(dinfo, 0);
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */
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put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
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/* flag byte: not interlaced, no local color map */
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putc(0x00, dinfo->pub.output_file);
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/* Write Initial Code Size byte */
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putc(InitCodeSize, dinfo->pub.output_file);
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/* Initialize for LZW compression of image data */
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compress_init(dinfo, InitCodeSize+1);
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}
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/*
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* Startup: write the file header.
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*/
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METHODDEF void
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start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
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{
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gif_dest_ptr dest = (gif_dest_ptr) dinfo;
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if (cinfo->quantize_colors)
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emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);
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else
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emit_header(dest, 256, (JSAMPARRAY) NULL);
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}
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/*
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* Write some pixel data.
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* In this module rows_supplied will always be 1.
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*/
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METHODDEF void
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put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo,
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JDIMENSION rows_supplied)
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{
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gif_dest_ptr dest = (gif_dest_ptr) dinfo;
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register JSAMPROW ptr;
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register JDIMENSION col;
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ptr = dest->pub.buffer[0];
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for (col = cinfo->output_width; col > 0; col--) {
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compress_byte(dest, GETJSAMPLE(*ptr++));
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}
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}
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/*
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* Finish up at the end of the file.
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*/
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METHODDEF void
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finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
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{
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gif_dest_ptr dest = (gif_dest_ptr) dinfo;
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/* Flush LZW mechanism */
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compress_term(dest);
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/* Write a zero-length data block to end the series */
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putc(0, dest->pub.output_file);
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/* Write the GIF terminator mark */
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putc(';', dest->pub.output_file);
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/* Make sure we wrote the output file OK */
|
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fflush(dest->pub.output_file);
|
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if (ferror(dest->pub.output_file))
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||||
ERREXIT(cinfo, JERR_FILE_WRITE);
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||||
}
|
||||
|
||||
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||||
/*
|
||||
* The module selection routine for GIF format output.
|
||||
*/
|
||||
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||||
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;
|
||||
|
||||
/* Allocate space for hash table */
|
||||
dest->hash_code = (code_int *)
|
||||
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
|
||||
HSIZE * SIZEOF(code_int));
|
||||
dest->hash_value = (hash_entry FAR *)
|
||||
(*cinfo->mem->alloc_large) ((j_common_ptr) cinfo, JPOOL_IMAGE,
|
||||
HSIZE * SIZEOF(hash_entry));
|
||||
|
||||
return (djpeg_dest_ptr) dest;
|
||||
}
|
||||
|
||||
#endif /* GIF_SUPPORTED */
|
||||
Reference in New Issue
Block a user