1 /* 2 * wrgif.c 3 * 4 * Copyright (C) 1991-1997, Thomas G. Lane. 5 * This file is part of the Independent JPEG Group's software. 6 * For conditions of distribution and use, see the accompanying README file. 7 * 8 * This file contains routines to write output images in GIF format. 9 * 10 ************************************************************************** 11 * NOTE: to avoid entanglements with Unisys' patent on LZW compression, * 12 * this code has been modified to output "uncompressed GIF" files. * 13 * There is no trace of the LZW algorithm in this file. * 14 ************************************************************************** 15 * 16 * These routines may need modification for non-Unix environments or 17 * specialized applications. As they stand, they assume output to 18 * an ordinary stdio stream. 19 */ 20 21 /* 22 * This code is loosely based on ppmtogif from the PBMPLUS distribution 23 * of Feb. 1991. That file contains the following copyright notice: 24 * Based on GIFENCODE by David Rowley <mgardi (at) watdscu.waterloo.edu>. 25 * Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al. 26 * Copyright (C) 1989 by Jef Poskanzer. 27 * Permission to use, copy, modify, and distribute this software and its 28 * documentation for any purpose and without fee is hereby granted, provided 29 * that the above copyright notice appear in all copies and that both that 30 * copyright notice and this permission notice appear in supporting 31 * documentation. This software is provided "as is" without express or 32 * implied warranty. 33 * 34 * We are also required to state that 35 * "The Graphics Interchange Format(c) is the Copyright property of 36 * CompuServe Incorporated. GIF(sm) is a Service Mark property of 37 * CompuServe Incorporated." 38 */ 39 40 #include "cdjpeg.h" /* Common decls for cjpeg/djpeg applications */ 41 42 #ifdef GIF_SUPPORTED 43 44 45 /* Private version of data destination object */ 46 47 typedef struct { 48 struct djpeg_dest_struct pub; /* public fields */ 49 50 j_decompress_ptr cinfo; /* back link saves passing separate parm */ 51 52 /* State for packing variable-width codes into a bitstream */ 53 int n_bits; /* current number of bits/code */ 54 int maxcode; /* maximum code, given n_bits */ 55 INT32 cur_accum; /* holds bits not yet output */ 56 int cur_bits; /* # of bits in cur_accum */ 57 58 /* State for GIF code assignment */ 59 int ClearCode; /* clear code (doesn't change) */ 60 int EOFCode; /* EOF code (ditto) */ 61 int code_counter; /* counts output symbols */ 62 63 /* GIF data packet construction buffer */ 64 int bytesinpkt; /* # of bytes in current packet */ 65 char packetbuf[256]; /* workspace for accumulating packet */ 66 67 } gif_dest_struct; 68 69 typedef gif_dest_struct * gif_dest_ptr; 70 71 /* Largest value that will fit in N bits */ 72 #define MAXCODE(n_bits) ((1 << (n_bits)) - 1) 73 74 75 /* 76 * Routines to package finished data bytes into GIF data blocks. 77 * A data block consists of a count byte (1..255) and that many data bytes. 78 */ 79 80 LOCAL(void) 81 flush_packet (gif_dest_ptr dinfo) 82 /* flush any accumulated data */ 83 { 84 if (dinfo->bytesinpkt > 0) { /* never write zero-length packet */ 85 dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++; 86 if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt) 87 != (size_t) dinfo->bytesinpkt) 88 ERREXIT(dinfo->cinfo, JERR_FILE_WRITE); 89 dinfo->bytesinpkt = 0; 90 } 91 } 92 93 94 /* Add a character to current packet; flush to disk if necessary */ 95 #define CHAR_OUT(dinfo,c) \ 96 { (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c); \ 97 if ((dinfo)->bytesinpkt >= 255) \ 98 flush_packet(dinfo); \ 99 } 100 101 102 /* Routine to convert variable-width codes into a byte stream */ 103 104 LOCAL(void) 105 output (gif_dest_ptr dinfo, int code) 106 /* Emit a code of n_bits bits */ 107 /* Uses cur_accum and cur_bits to reblock into 8-bit bytes */ 108 { 109 dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits; 110 dinfo->cur_bits += dinfo->n_bits; 111 112 while (dinfo->cur_bits >= 8) { 113 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 114 dinfo->cur_accum >>= 8; 115 dinfo->cur_bits -= 8; 116 } 117 } 118 119 120 /* The pseudo-compression algorithm. 121 * 122 * In this module we simply output each pixel value as a separate symbol; 123 * thus, no compression occurs. In fact, there is expansion of one bit per 124 * pixel, because we use a symbol width one bit wider than the pixel width. 125 * 126 * GIF ordinarily uses variable-width symbols, and the decoder will expect 127 * to ratchet up the symbol width after a fixed number of symbols. 128 * To simplify the logic and keep the expansion penalty down, we emit a 129 * GIF Clear code to reset the decoder just before the width would ratchet up. 130 * Thus, all the symbols in the output file will have the same bit width. 131 * Note that emitting the Clear codes at the right times is a mere matter of 132 * counting output symbols and is in no way dependent on the LZW patent. 133 * 134 * With a small basic pixel width (low color count), Clear codes will be 135 * needed very frequently, causing the file to expand even more. So this 136 * simplistic approach wouldn't work too well on bilevel images, for example. 137 * But for output of JPEG conversions the pixel width will usually be 8 bits 138 * (129 to 256 colors), so the overhead added by Clear symbols is only about 139 * one symbol in every 256. 140 */ 141 142 LOCAL(void) 143 compress_init (gif_dest_ptr dinfo, int i_bits) 144 /* Initialize pseudo-compressor */ 145 { 146 /* init all the state variables */ 147 dinfo->n_bits = i_bits; 148 dinfo->maxcode = MAXCODE(dinfo->n_bits); 149 dinfo->ClearCode = (1 << (i_bits - 1)); 150 dinfo->EOFCode = dinfo->ClearCode + 1; 151 dinfo->code_counter = dinfo->ClearCode + 2; 152 /* init output buffering vars */ 153 dinfo->bytesinpkt = 0; 154 dinfo->cur_accum = 0; 155 dinfo->cur_bits = 0; 156 /* GIF specifies an initial Clear code */ 157 output(dinfo, dinfo->ClearCode); 158 } 159 160 161 LOCAL(void) 162 compress_pixel (gif_dest_ptr dinfo, int c) 163 /* Accept and "compress" one pixel value. 164 * The given value must be less than n_bits wide. 165 */ 166 { 167 /* Output the given pixel value as a symbol. */ 168 output(dinfo, c); 169 /* Issue Clear codes often enough to keep the reader from ratcheting up 170 * its symbol size. 171 */ 172 if (dinfo->code_counter < dinfo->maxcode) { 173 dinfo->code_counter++; 174 } else { 175 output(dinfo, dinfo->ClearCode); 176 dinfo->code_counter = dinfo->ClearCode + 2; /* reset the counter */ 177 } 178 } 179 180 181 LOCAL(void) 182 compress_term (gif_dest_ptr dinfo) 183 /* Clean up at end */ 184 { 185 /* Send an EOF code */ 186 output(dinfo, dinfo->EOFCode); 187 /* Flush the bit-packing buffer */ 188 if (dinfo->cur_bits > 0) { 189 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 190 } 191 /* Flush the packet buffer */ 192 flush_packet(dinfo); 193 } 194 195 196 /* GIF header construction */ 197 198 199 LOCAL(void) 200 put_word (gif_dest_ptr dinfo, unsigned int w) 201 /* Emit a 16-bit word, LSB first */ 202 { 203 putc(w & 0xFF, dinfo->pub.output_file); 204 putc((w >> 8) & 0xFF, dinfo->pub.output_file); 205 } 206 207 208 LOCAL(void) 209 put_3bytes (gif_dest_ptr dinfo, int val) 210 /* Emit 3 copies of same byte value --- handy subr for colormap construction */ 211 { 212 putc(val, dinfo->pub.output_file); 213 putc(val, dinfo->pub.output_file); 214 putc(val, dinfo->pub.output_file); 215 } 216 217 218 LOCAL(void) 219 emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap) 220 /* Output the GIF file header, including color map */ 221 /* If colormap==NULL, synthesize a gray-scale colormap */ 222 { 223 int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte; 224 int cshift = dinfo->cinfo->data_precision - 8; 225 int i; 226 227 if (num_colors > 256) 228 ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors); 229 /* Compute bits/pixel and related values */ 230 BitsPerPixel = 1; 231 while (num_colors > (1 << BitsPerPixel)) 232 BitsPerPixel++; 233 ColorMapSize = 1 << BitsPerPixel; 234 if (BitsPerPixel <= 1) 235 InitCodeSize = 2; 236 else 237 InitCodeSize = BitsPerPixel; 238 /* 239 * Write the GIF header. 240 * Note that we generate a plain GIF87 header for maximum compatibility. 241 */ 242 putc('G', dinfo->pub.output_file); 243 putc('I', dinfo->pub.output_file); 244 putc('F', dinfo->pub.output_file); 245 putc('8', dinfo->pub.output_file); 246 putc('7', dinfo->pub.output_file); 247 putc('a', dinfo->pub.output_file); 248 /* Write the Logical Screen Descriptor */ 249 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); 250 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 251 FlagByte = 0x80; /* Yes, there is a global color table */ 252 FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */ 253 FlagByte |= (BitsPerPixel-1); /* size of global color table */ 254 putc(FlagByte, dinfo->pub.output_file); 255 putc(0, dinfo->pub.output_file); /* Background color index */ 256 putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */ 257 /* Write the Global Color Map */ 258 /* If the color map is more than 8 bits precision, */ 259 /* we reduce it to 8 bits by shifting */ 260 for (i=0; i < ColorMapSize; i++) { 261 if (i < num_colors) { 262 if (colormap != NULL) { 263 if (dinfo->cinfo->out_color_space == JCS_RGB) { 264 /* Normal case: RGB color map */ 265 putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file); 266 putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file); 267 putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file); 268 } else { 269 /* Grayscale "color map": possible if quantizing grayscale image */ 270 put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift); 271 } 272 } else { 273 /* Create a gray-scale map of num_colors values, range 0..255 */ 274 put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1)); 275 } 276 } else { 277 /* fill out the map to a power of 2 */ 278 put_3bytes(dinfo, 0); 279 } 280 } 281 /* Write image separator and Image Descriptor */ 282 putc(',', dinfo->pub.output_file); /* separator */ 283 put_word(dinfo, 0); /* left/top offset */ 284 put_word(dinfo, 0); 285 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */ 286 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 287 /* flag byte: not interlaced, no local color map */ 288 putc(0x00, dinfo->pub.output_file); 289 /* Write Initial Code Size byte */ 290 putc(InitCodeSize, dinfo->pub.output_file); 291 292 /* Initialize for "compression" of image data */ 293 compress_init(dinfo, InitCodeSize+1); 294 } 295 296 297 /* 298 * Startup: write the file header. 299 */ 300 301 METHODDEF(void) 302 start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 303 { 304 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 305 306 if (cinfo->quantize_colors) 307 emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap); 308 else 309 emit_header(dest, 256, (JSAMPARRAY) NULL); 310 } 311 312 313 /* 314 * Write some pixel data. 315 * In this module rows_supplied will always be 1. 316 */ 317 318 METHODDEF(void) 319 put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo, 320 JDIMENSION rows_supplied) 321 { 322 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 323 register JSAMPROW ptr; 324 register JDIMENSION col; 325 326 ptr = dest->pub.buffer[0]; 327 for (col = cinfo->output_width; col > 0; col--) { 328 compress_pixel(dest, GETJSAMPLE(*ptr++)); 329 } 330 } 331 332 333 /* 334 * Finish up at the end of the file. 335 */ 336 337 METHODDEF(void) 338 finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 339 { 340 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 341 342 /* Flush "compression" mechanism */ 343 compress_term(dest); 344 /* Write a zero-length data block to end the series */ 345 putc(0, dest->pub.output_file); 346 /* Write the GIF terminator mark */ 347 putc(';', dest->pub.output_file); 348 /* Make sure we wrote the output file OK */ 349 fflush(dest->pub.output_file); 350 if (ferror(dest->pub.output_file)) 351 ERREXIT(cinfo, JERR_FILE_WRITE); 352 } 353 354 355 /* 356 * The module selection routine for GIF format output. 357 */ 358 359 GLOBAL(djpeg_dest_ptr) 360 jinit_write_gif (j_decompress_ptr cinfo) 361 { 362 gif_dest_ptr dest; 363 364 /* Create module interface object, fill in method pointers */ 365 dest = (gif_dest_ptr) 366 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 367 SIZEOF(gif_dest_struct)); 368 dest->cinfo = cinfo; /* make back link for subroutines */ 369 dest->pub.start_output = start_output_gif; 370 dest->pub.put_pixel_rows = put_pixel_rows; 371 dest->pub.finish_output = finish_output_gif; 372 373 if (cinfo->out_color_space != JCS_GRAYSCALE && 374 cinfo->out_color_space != JCS_RGB) 375 ERREXIT(cinfo, JERR_GIF_COLORSPACE); 376 377 /* Force quantization if color or if > 8 bits input */ 378 if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) { 379 /* Force quantization to at most 256 colors */ 380 cinfo->quantize_colors = TRUE; 381 if (cinfo->desired_number_of_colors > 256) 382 cinfo->desired_number_of_colors = 256; 383 } 384 385 /* Calculate output image dimensions so we can allocate space */ 386 jpeg_calc_output_dimensions(cinfo); 387 388 if (cinfo->output_components != 1) /* safety check: just one component? */ 389 ERREXIT(cinfo, JERR_GIF_BUG); 390 391 /* Create decompressor output buffer. */ 392 dest->pub.buffer = (*cinfo->mem->alloc_sarray) 393 ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1); 394 dest->pub.buffer_height = 1; 395 396 return (djpeg_dest_ptr) dest; 397 } 398 399 #endif /* GIF_SUPPORTED */ 400
