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plt-scheme  4.2.1
wrgif.c
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00001 /*
00002  * wrgif.c
00003  *
00004  * Copyright (C) 1991-1997, Thomas G. Lane.
00005  * This file is part of the Independent JPEG Group's software.
00006  * For conditions of distribution and use, see the accompanying README file.
00007  *
00008  * This file contains routines to write output images in GIF format.
00009  *
00010  **************************************************************************
00011  * NOTE: to avoid entanglements with Unisys' patent on LZW compression,   *
00012  * this code has been modified to output "uncompressed GIF" files.        *
00013  * There is no trace of the LZW algorithm in this file.                   *
00014  **************************************************************************
00015  *
00016  * These routines may need modification for non-Unix environments or
00017  * specialized applications.  As they stand, they assume output to
00018  * an ordinary stdio stream.
00019  */
00020 
00021 /*
00022  * This code is loosely based on ppmtogif from the PBMPLUS distribution
00023  * of Feb. 1991.  That file contains the following copyright notice:
00024  *    Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>.
00025  *    Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al.
00026  *    Copyright (C) 1989 by Jef Poskanzer.
00027  *    Permission to use, copy, modify, and distribute this software and its
00028  *    documentation for any purpose and without fee is hereby granted, provided
00029  *    that the above copyright notice appear in all copies and that both that
00030  *    copyright notice and this permission notice appear in supporting
00031  *    documentation.  This software is provided "as is" without express or
00032  *    implied warranty.
00033  *
00034  * We are also required to state that
00035  *    "The Graphics Interchange Format(c) is the Copyright property of
00036  *    CompuServe Incorporated. GIF(sm) is a Service Mark property of
00037  *    CompuServe Incorporated."
00038  */
00039 
00040 #include "cdjpeg.h"         /* Common decls for cjpeg/djpeg applications */
00041 
00042 #ifdef GIF_SUPPORTED
00043 
00044 
00045 /* Private version of data destination object */
00046 
00047 typedef struct {
00048   struct djpeg_dest_struct pub;    /* public fields */
00049 
00050   j_decompress_ptr cinfo;   /* back link saves passing separate parm */
00051 
00052   /* State for packing variable-width codes into a bitstream */
00053   int n_bits;               /* current number of bits/code */
00054   int maxcode;                     /* maximum code, given n_bits */
00055   INT32 cur_accum;          /* holds bits not yet output */
00056   int cur_bits;                    /* # of bits in cur_accum */
00057 
00058   /* State for GIF code assignment */
00059   int ClearCode;            /* clear code (doesn't change) */
00060   int EOFCode;                     /* EOF code (ditto) */
00061   int code_counter;         /* counts output symbols */
00062 
00063   /* GIF data packet construction buffer */
00064   int bytesinpkt;           /* # of bytes in current packet */
00065   char packetbuf[256];             /* workspace for accumulating packet */
00066 
00067 } gif_dest_struct;
00068 
00069 typedef gif_dest_struct * gif_dest_ptr;
00070 
00071 /* Largest value that will fit in N bits */
00072 #define MAXCODE(n_bits)     ((1 << (n_bits)) - 1)
00073 
00074 
00075 /*
00076  * Routines to package finished data bytes into GIF data blocks.
00077  * A data block consists of a count byte (1..255) and that many data bytes.
00078  */
00079 
00080 LOCAL(void)
00081 flush_packet (gif_dest_ptr dinfo)
00082 /* flush any accumulated data */
00083 {
00084   if (dinfo->bytesinpkt > 0) {     /* never write zero-length packet */
00085     dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++;
00086     if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt)
00087        != (size_t) dinfo->bytesinpkt)
00088       ERREXIT(dinfo->cinfo, JERR_FILE_WRITE);
00089     dinfo->bytesinpkt = 0;
00090   }
00091 }
00092 
00093 
00094 /* Add a character to current packet; flush to disk if necessary */
00095 #define CHAR_OUT(dinfo,c)  \
00096        { (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c);  \
00097            if ((dinfo)->bytesinpkt >= 255)  \
00098              flush_packet(dinfo);  \
00099        }
00100 
00101 
00102 /* Routine to convert variable-width codes into a byte stream */
00103 
00104 LOCAL(void)
00105 output (gif_dest_ptr dinfo, int code)
00106 /* Emit a code of n_bits bits */
00107 /* Uses cur_accum and cur_bits to reblock into 8-bit bytes */
00108 {
00109   dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits;
00110   dinfo->cur_bits += dinfo->n_bits;
00111 
00112   while (dinfo->cur_bits >= 8) {
00113     CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
00114     dinfo->cur_accum >>= 8;
00115     dinfo->cur_bits -= 8;
00116   }
00117 }
00118 
00119 
00120 /* The pseudo-compression algorithm.
00121  *
00122  * In this module we simply output each pixel value as a separate symbol;
00123  * thus, no compression occurs.  In fact, there is expansion of one bit per
00124  * pixel, because we use a symbol width one bit wider than the pixel width.
00125  *
00126  * GIF ordinarily uses variable-width symbols, and the decoder will expect
00127  * to ratchet up the symbol width after a fixed number of symbols.
00128  * To simplify the logic and keep the expansion penalty down, we emit a
00129  * GIF Clear code to reset the decoder just before the width would ratchet up.
00130  * Thus, all the symbols in the output file will have the same bit width.
00131  * Note that emitting the Clear codes at the right times is a mere matter of
00132  * counting output symbols and is in no way dependent on the LZW patent.
00133  *
00134  * With a small basic pixel width (low color count), Clear codes will be
00135  * needed very frequently, causing the file to expand even more.  So this
00136  * simplistic approach wouldn't work too well on bilevel images, for example.
00137  * But for output of JPEG conversions the pixel width will usually be 8 bits
00138  * (129 to 256 colors), so the overhead added by Clear symbols is only about
00139  * one symbol in every 256.
00140  */
00141 
00142 LOCAL(void)
00143 compress_init (gif_dest_ptr dinfo, int i_bits)
00144 /* Initialize pseudo-compressor */
00145 {
00146   /* init all the state variables */
00147   dinfo->n_bits = i_bits;
00148   dinfo->maxcode = MAXCODE(dinfo->n_bits);
00149   dinfo->ClearCode = (1 << (i_bits - 1));
00150   dinfo->EOFCode = dinfo->ClearCode + 1;
00151   dinfo->code_counter = dinfo->ClearCode + 2;
00152   /* init output buffering vars */
00153   dinfo->bytesinpkt = 0;
00154   dinfo->cur_accum = 0;
00155   dinfo->cur_bits = 0;
00156   /* GIF specifies an initial Clear code */
00157   output(dinfo, dinfo->ClearCode);
00158 }
00159 
00160 
00161 LOCAL(void)
00162 compress_pixel (gif_dest_ptr dinfo, int c)
00163 /* Accept and "compress" one pixel value.
00164  * The given value must be less than n_bits wide.
00165  */
00166 {
00167   /* Output the given pixel value as a symbol. */
00168   output(dinfo, c);
00169   /* Issue Clear codes often enough to keep the reader from ratcheting up
00170    * its symbol size.
00171    */
00172   if (dinfo->code_counter < dinfo->maxcode) {
00173     dinfo->code_counter++;
00174   } else {
00175     output(dinfo, dinfo->ClearCode);
00176     dinfo->code_counter = dinfo->ClearCode + 2;  /* reset the counter */
00177   }
00178 }
00179 
00180 
00181 LOCAL(void)
00182 compress_term (gif_dest_ptr dinfo)
00183 /* Clean up at end */
00184 {
00185   /* Send an EOF code */
00186   output(dinfo, dinfo->EOFCode);
00187   /* Flush the bit-packing buffer */
00188   if (dinfo->cur_bits > 0) {
00189     CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF);
00190   }
00191   /* Flush the packet buffer */
00192   flush_packet(dinfo);
00193 }
00194 
00195 
00196 /* GIF header construction */
00197 
00198 
00199 LOCAL(void)
00200 put_word (gif_dest_ptr dinfo, unsigned int w)
00201 /* Emit a 16-bit word, LSB first */
00202 {
00203   putc(w & 0xFF, dinfo->pub.output_file);
00204   putc((w >> 8) & 0xFF, dinfo->pub.output_file);
00205 }
00206 
00207 
00208 LOCAL(void)
00209 put_3bytes (gif_dest_ptr dinfo, int val)
00210 /* Emit 3 copies of same byte value --- handy subr for colormap construction */
00211 {
00212   putc(val, dinfo->pub.output_file);
00213   putc(val, dinfo->pub.output_file);
00214   putc(val, dinfo->pub.output_file);
00215 }
00216 
00217 
00218 LOCAL(void)
00219 emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap)
00220 /* Output the GIF file header, including color map */
00221 /* If colormap==NULL, synthesize a gray-scale colormap */
00222 {
00223   int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte;
00224   int cshift = dinfo->cinfo->data_precision - 8;
00225   int i;
00226 
00227   if (num_colors > 256)
00228     ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors);
00229   /* Compute bits/pixel and related values */
00230   BitsPerPixel = 1;
00231   while (num_colors > (1 << BitsPerPixel))
00232     BitsPerPixel++;
00233   ColorMapSize = 1 << BitsPerPixel;
00234   if (BitsPerPixel <= 1)
00235     InitCodeSize = 2;
00236   else
00237     InitCodeSize = BitsPerPixel;
00238   /*
00239    * Write the GIF header.
00240    * Note that we generate a plain GIF87 header for maximum compatibility.
00241    */
00242   putc('G', dinfo->pub.output_file);
00243   putc('I', dinfo->pub.output_file);
00244   putc('F', dinfo->pub.output_file);
00245   putc('8', dinfo->pub.output_file);
00246   putc('7', dinfo->pub.output_file);
00247   putc('a', dinfo->pub.output_file);
00248   /* Write the Logical Screen Descriptor */
00249   put_word(dinfo, (unsigned int) dinfo->cinfo->output_width);
00250   put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
00251   FlagByte = 0x80;          /* Yes, there is a global color table */
00252   FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */
00253   FlagByte |= (BitsPerPixel-1);    /* size of global color table */
00254   putc(FlagByte, dinfo->pub.output_file);
00255   putc(0, dinfo->pub.output_file); /* Background color index */
00256   putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */
00257   /* Write the Global Color Map */
00258   /* If the color map is more than 8 bits precision, */
00259   /* we reduce it to 8 bits by shifting */
00260   for (i=0; i < ColorMapSize; i++) {
00261     if (i < num_colors) {
00262       if (colormap != NULL) {
00263        if (dinfo->cinfo->out_color_space == JCS_RGB) {
00264          /* Normal case: RGB color map */
00265          putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file);
00266          putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file);
00267          putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file);
00268        } else {
00269          /* Grayscale "color map": possible if quantizing grayscale image */
00270          put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift);
00271        }
00272       } else {
00273        /* Create a gray-scale map of num_colors values, range 0..255 */
00274        put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1));
00275       }
00276     } else {
00277       /* fill out the map to a power of 2 */
00278       put_3bytes(dinfo, 0);
00279     }
00280   }
00281   /* Write image separator and Image Descriptor */
00282   putc(',', dinfo->pub.output_file); /* separator */
00283   put_word(dinfo, 0);              /* left/top offset */
00284   put_word(dinfo, 0);
00285   put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */
00286   put_word(dinfo, (unsigned int) dinfo->cinfo->output_height);
00287   /* flag byte: not interlaced, no local color map */
00288   putc(0x00, dinfo->pub.output_file);
00289   /* Write Initial Code Size byte */
00290   putc(InitCodeSize, dinfo->pub.output_file);
00291 
00292   /* Initialize for "compression" of image data */
00293   compress_init(dinfo, InitCodeSize+1);
00294 }
00295 
00296 
00297 /*
00298  * Startup: write the file header.
00299  */
00300 
00301 METHODDEF(void)
00302 start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
00303 {
00304   gif_dest_ptr dest = (gif_dest_ptr) dinfo;
00305 
00306   if (cinfo->quantize_colors)
00307     emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap);
00308   else
00309     emit_header(dest, 256, (JSAMPARRAY) NULL);
00310 }
00311 
00312 
00313 /*
00314  * Write some pixel data.
00315  * In this module rows_supplied will always be 1.
00316  */
00317 
00318 METHODDEF(void)
00319 put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo,
00320               JDIMENSION rows_supplied)
00321 {
00322   gif_dest_ptr dest = (gif_dest_ptr) dinfo;
00323   register JSAMPROW ptr;
00324   register JDIMENSION col;
00325 
00326   ptr = dest->pub.buffer[0];
00327   for (col = cinfo->output_width; col > 0; col--) {
00328     compress_pixel(dest, GETJSAMPLE(*ptr++));
00329   }
00330 }
00331 
00332 
00333 /*
00334  * Finish up at the end of the file.
00335  */
00336 
00337 METHODDEF(void)
00338 finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
00339 {
00340   gif_dest_ptr dest = (gif_dest_ptr) dinfo;
00341 
00342   /* Flush "compression" mechanism */
00343   compress_term(dest);
00344   /* Write a zero-length data block to end the series */
00345   putc(0, dest->pub.output_file);
00346   /* Write the GIF terminator mark */
00347   putc(';', dest->pub.output_file);
00348   /* Make sure we wrote the output file OK */
00349   fflush(dest->pub.output_file);
00350   if (ferror(dest->pub.output_file))
00351     ERREXIT(cinfo, JERR_FILE_WRITE);
00352 }
00353 
00354 
00355 /*
00356  * The module selection routine for GIF format output.
00357  */
00358 
00359 GLOBAL(djpeg_dest_ptr)
00360 jinit_write_gif (j_decompress_ptr cinfo)
00361 {
00362   gif_dest_ptr dest;
00363 
00364   /* Create module interface object, fill in method pointers */
00365   dest = (gif_dest_ptr)
00366       (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
00367                               SIZEOF(gif_dest_struct));
00368   dest->cinfo = cinfo;             /* make back link for subroutines */
00369   dest->pub.start_output = start_output_gif;
00370   dest->pub.put_pixel_rows = put_pixel_rows;
00371   dest->pub.finish_output = finish_output_gif;
00372 
00373   if (cinfo->out_color_space != JCS_GRAYSCALE &&
00374       cinfo->out_color_space != JCS_RGB)
00375     ERREXIT(cinfo, JERR_GIF_COLORSPACE);
00376 
00377   /* Force quantization if color or if > 8 bits input */
00378   if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) {
00379     /* Force quantization to at most 256 colors */
00380     cinfo->quantize_colors = TRUE;
00381     if (cinfo->desired_number_of_colors > 256)
00382       cinfo->desired_number_of_colors = 256;
00383   }
00384 
00385   /* Calculate output image dimensions so we can allocate space */
00386   jpeg_calc_output_dimensions(cinfo);
00387 
00388   if (cinfo->output_components != 1) /* safety check: just one component? */
00389     ERREXIT(cinfo, JERR_GIF_BUG);
00390 
00391   /* Create decompressor output buffer. */
00392   dest->pub.buffer = (*cinfo->mem->alloc_sarray)
00393     ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1);
00394   dest->pub.buffer_height = 1;
00395 
00396   return (djpeg_dest_ptr) dest;
00397 }
00398 
00399 #endif /* GIF_SUPPORTED */