1/* 2 * wrgif.c 3 * 4 * This file was part of the Independent JPEG Group's software: 5 * Copyright (C) 1991-1997, Thomas G. Lane. 6 * It was modified by The libjpeg-turbo Project to include only code relevant 7 * to libjpeg-turbo. 8 * For conditions of distribution and use, see the accompanying README file. 9 * 10 * This file contains routines to write output images in GIF format. 11 * 12 ************************************************************************** 13 * NOTE: to avoid entanglements with Unisys' patent on LZW compression, * 14 * this code has been modified to output "uncompressed GIF" files. * 15 * There is no trace of the LZW algorithm in this file. * 16 ************************************************************************** 17 * 18 * These routines may need modification for non-Unix environments or 19 * specialized applications. As they stand, they assume output to 20 * an ordinary stdio stream. 21 */ 22 23/* 24 * This code is loosely based on ppmtogif from the PBMPLUS distribution 25 * of Feb. 1991. That file contains the following copyright notice: 26 * Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>. 27 * Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al. 28 * Copyright (C) 1989 by Jef Poskanzer. 29 * Permission to use, copy, modify, and distribute this software and its 30 * documentation for any purpose and without fee is hereby granted, provided 31 * that the above copyright notice appear in all copies and that both that 32 * copyright notice and this permission notice appear in supporting 33 * documentation. This software is provided "as is" without express or 34 * implied warranty. 35 * 36 * We are also required to state that 37 * "The Graphics Interchange Format(c) is the Copyright property of 38 * CompuServe Incorporated. GIF(sm) is a Service Mark property of 39 * CompuServe Incorporated." 40 */ 41 42#include "cdjpeg.h" /* Common decls for cjpeg/djpeg applications */ 43 44#ifdef GIF_SUPPORTED 45 46 47/* Private version of data destination object */ 48 49typedef struct { 50 struct djpeg_dest_struct pub; /* public fields */ 51 52 j_decompress_ptr cinfo; /* back link saves passing separate parm */ 53 54 /* State for packing variable-width codes into a bitstream */ 55 int n_bits; /* current number of bits/code */ 56 int maxcode; /* maximum code, given n_bits */ 57 INT32 cur_accum; /* holds bits not yet output */ 58 int cur_bits; /* # of bits in cur_accum */ 59 60 /* State for GIF code assignment */ 61 int ClearCode; /* clear code (doesn't change) */ 62 int EOFCode; /* EOF code (ditto) */ 63 int code_counter; /* counts output symbols */ 64 65 /* GIF data packet construction buffer */ 66 int bytesinpkt; /* # of bytes in current packet */ 67 char packetbuf[256]; /* workspace for accumulating packet */ 68 69} gif_dest_struct; 70 71typedef gif_dest_struct * gif_dest_ptr; 72 73/* Largest value that will fit in N bits */ 74#define MAXCODE(n_bits) ((1 << (n_bits)) - 1) 75 76 77/* 78 * Routines to package finished data bytes into GIF data blocks. 79 * A data block consists of a count byte (1..255) and that many data bytes. 80 */ 81 82LOCAL(void) 83flush_packet (gif_dest_ptr dinfo) 84/* flush any accumulated data */ 85{ 86 if (dinfo->bytesinpkt > 0) { /* never write zero-length packet */ 87 dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++; 88 if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt) 89 != (size_t) dinfo->bytesinpkt) 90 ERREXIT(dinfo->cinfo, JERR_FILE_WRITE); 91 dinfo->bytesinpkt = 0; 92 } 93} 94 95 96/* Add a character to current packet; flush to disk if necessary */ 97#define CHAR_OUT(dinfo,c) \ 98 { (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c); \ 99 if ((dinfo)->bytesinpkt >= 255) \ 100 flush_packet(dinfo); \ 101 } 102 103 104/* Routine to convert variable-width codes into a byte stream */ 105 106LOCAL(void) 107output (gif_dest_ptr dinfo, int code) 108/* Emit a code of n_bits bits */ 109/* Uses cur_accum and cur_bits to reblock into 8-bit bytes */ 110{ 111 dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits; 112 dinfo->cur_bits += dinfo->n_bits; 113 114 while (dinfo->cur_bits >= 8) { 115 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 116 dinfo->cur_accum >>= 8; 117 dinfo->cur_bits -= 8; 118 } 119} 120 121 122/* The pseudo-compression algorithm. 123 * 124 * In this module we simply output each pixel value as a separate symbol; 125 * thus, no compression occurs. In fact, there is expansion of one bit per 126 * pixel, because we use a symbol width one bit wider than the pixel width. 127 * 128 * GIF ordinarily uses variable-width symbols, and the decoder will expect 129 * to ratchet up the symbol width after a fixed number of symbols. 130 * To simplify the logic and keep the expansion penalty down, we emit a 131 * GIF Clear code to reset the decoder just before the width would ratchet up. 132 * Thus, all the symbols in the output file will have the same bit width. 133 * Note that emitting the Clear codes at the right times is a mere matter of 134 * counting output symbols and is in no way dependent on the LZW patent. 135 * 136 * With a small basic pixel width (low color count), Clear codes will be 137 * needed very frequently, causing the file to expand even more. So this 138 * simplistic approach wouldn't work too well on bilevel images, for example. 139 * But for output of JPEG conversions the pixel width will usually be 8 bits 140 * (129 to 256 colors), so the overhead added by Clear symbols is only about 141 * one symbol in every 256. 142 */ 143 144LOCAL(void) 145compress_init (gif_dest_ptr dinfo, int i_bits) 146/* Initialize pseudo-compressor */ 147{ 148 /* init all the state variables */ 149 dinfo->n_bits = i_bits; 150 dinfo->maxcode = MAXCODE(dinfo->n_bits); 151 dinfo->ClearCode = (1 << (i_bits - 1)); 152 dinfo->EOFCode = dinfo->ClearCode + 1; 153 dinfo->code_counter = dinfo->ClearCode + 2; 154 /* init output buffering vars */ 155 dinfo->bytesinpkt = 0; 156 dinfo->cur_accum = 0; 157 dinfo->cur_bits = 0; 158 /* GIF specifies an initial Clear code */ 159 output(dinfo, dinfo->ClearCode); 160} 161 162 163LOCAL(void) 164compress_pixel (gif_dest_ptr dinfo, int c) 165/* Accept and "compress" one pixel value. 166 * The given value must be less than n_bits wide. 167 */ 168{ 169 /* Output the given pixel value as a symbol. */ 170 output(dinfo, c); 171 /* Issue Clear codes often enough to keep the reader from ratcheting up 172 * its symbol size. 173 */ 174 if (dinfo->code_counter < dinfo->maxcode) { 175 dinfo->code_counter++; 176 } else { 177 output(dinfo, dinfo->ClearCode); 178 dinfo->code_counter = dinfo->ClearCode + 2; /* reset the counter */ 179 } 180} 181 182 183LOCAL(void) 184compress_term (gif_dest_ptr dinfo) 185/* Clean up at end */ 186{ 187 /* Send an EOF code */ 188 output(dinfo, dinfo->EOFCode); 189 /* Flush the bit-packing buffer */ 190 if (dinfo->cur_bits > 0) { 191 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 192 } 193 /* Flush the packet buffer */ 194 flush_packet(dinfo); 195} 196 197 198/* GIF header construction */ 199 200 201LOCAL(void) 202put_word (gif_dest_ptr dinfo, unsigned int w) 203/* Emit a 16-bit word, LSB first */ 204{ 205 putc(w & 0xFF, dinfo->pub.output_file); 206 putc((w >> 8) & 0xFF, dinfo->pub.output_file); 207} 208 209 210LOCAL(void) 211put_3bytes (gif_dest_ptr dinfo, int val) 212/* Emit 3 copies of same byte value --- handy subr for colormap construction */ 213{ 214 putc(val, dinfo->pub.output_file); 215 putc(val, dinfo->pub.output_file); 216 putc(val, dinfo->pub.output_file); 217} 218 219 220LOCAL(void) 221emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap) 222/* Output the GIF file header, including color map */ 223/* If colormap==NULL, synthesize a grayscale colormap */ 224{ 225 int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte; 226 int cshift = dinfo->cinfo->data_precision - 8; 227 int i; 228 229 if (num_colors > 256) 230 ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors); 231 /* Compute bits/pixel and related values */ 232 BitsPerPixel = 1; 233 while (num_colors > (1 << BitsPerPixel)) 234 BitsPerPixel++; 235 ColorMapSize = 1 << BitsPerPixel; 236 if (BitsPerPixel <= 1) 237 InitCodeSize = 2; 238 else 239 InitCodeSize = BitsPerPixel; 240 /* 241 * Write the GIF header. 242 * Note that we generate a plain GIF87 header for maximum compatibility. 243 */ 244 putc('G', dinfo->pub.output_file); 245 putc('I', dinfo->pub.output_file); 246 putc('F', dinfo->pub.output_file); 247 putc('8', dinfo->pub.output_file); 248 putc('7', dinfo->pub.output_file); 249 putc('a', dinfo->pub.output_file); 250 /* Write the Logical Screen Descriptor */ 251 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); 252 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 253 FlagByte = 0x80; /* Yes, there is a global color table */ 254 FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */ 255 FlagByte |= (BitsPerPixel-1); /* size of global color table */ 256 putc(FlagByte, dinfo->pub.output_file); 257 putc(0, dinfo->pub.output_file); /* Background color index */ 258 putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */ 259 /* Write the Global Color Map */ 260 /* If the color map is more than 8 bits precision, */ 261 /* we reduce it to 8 bits by shifting */ 262 for (i=0; i < ColorMapSize; i++) { 263 if (i < num_colors) { 264 if (colormap != NULL) { 265 if (dinfo->cinfo->out_color_space == JCS_RGB) { 266 /* Normal case: RGB color map */ 267 putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file); 268 putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file); 269 putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file); 270 } else { 271 /* Grayscale "color map": possible if quantizing grayscale image */ 272 put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift); 273 } 274 } else { 275 /* Create a grayscale map of num_colors values, range 0..255 */ 276 put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1)); 277 } 278 } else { 279 /* fill out the map to a power of 2 */ 280 put_3bytes(dinfo, 0); 281 } 282 } 283 /* Write image separator and Image Descriptor */ 284 putc(',', dinfo->pub.output_file); /* separator */ 285 put_word(dinfo, 0); /* left/top offset */ 286 put_word(dinfo, 0); 287 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */ 288 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 289 /* flag byte: not interlaced, no local color map */ 290 putc(0x00, dinfo->pub.output_file); 291 /* Write Initial Code Size byte */ 292 putc(InitCodeSize, dinfo->pub.output_file); 293 294 /* Initialize for "compression" of image data */ 295 compress_init(dinfo, InitCodeSize+1); 296} 297 298 299/* 300 * Startup: write the file header. 301 */ 302 303METHODDEF(void) 304start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 305{ 306 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 307 308 if (cinfo->quantize_colors) 309 emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap); 310 else 311 emit_header(dest, 256, (JSAMPARRAY) NULL); 312} 313 314 315/* 316 * Write some pixel data. 317 * In this module rows_supplied will always be 1. 318 */ 319 320METHODDEF(void) 321put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo, 322 JDIMENSION rows_supplied) 323{ 324 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 325 register JSAMPROW ptr; 326 register JDIMENSION col; 327 328 ptr = dest->pub.buffer[0]; 329 for (col = cinfo->output_width; col > 0; col--) { 330 compress_pixel(dest, GETJSAMPLE(*ptr++)); 331 } 332} 333 334 335/* 336 * Finish up at the end of the file. 337 */ 338 339METHODDEF(void) 340finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 341{ 342 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 343 344 /* Flush "compression" mechanism */ 345 compress_term(dest); 346 /* Write a zero-length data block to end the series */ 347 putc(0, dest->pub.output_file); 348 /* Write the GIF terminator mark */ 349 putc(';', dest->pub.output_file); 350 /* Make sure we wrote the output file OK */ 351 fflush(dest->pub.output_file); 352 if (ferror(dest->pub.output_file)) 353 ERREXIT(cinfo, JERR_FILE_WRITE); 354} 355 356 357/* 358 * The module selection routine for GIF format output. 359 */ 360 361GLOBAL(djpeg_dest_ptr) 362jinit_write_gif (j_decompress_ptr cinfo) 363{ 364 gif_dest_ptr dest; 365 366 /* Create module interface object, fill in method pointers */ 367 dest = (gif_dest_ptr) 368 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 369 sizeof(gif_dest_struct)); 370 dest->cinfo = cinfo; /* make back link for subroutines */ 371 dest->pub.start_output = start_output_gif; 372 dest->pub.put_pixel_rows = put_pixel_rows; 373 dest->pub.finish_output = finish_output_gif; 374 375 if (cinfo->out_color_space != JCS_GRAYSCALE && 376 cinfo->out_color_space != JCS_RGB) 377 ERREXIT(cinfo, JERR_GIF_COLORSPACE); 378 379 /* Force quantization if color or if > 8 bits input */ 380 if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) { 381 /* Force quantization to at most 256 colors */ 382 cinfo->quantize_colors = TRUE; 383 if (cinfo->desired_number_of_colors > 256) 384 cinfo->desired_number_of_colors = 256; 385 } 386 387 /* Calculate output image dimensions so we can allocate space */ 388 jpeg_calc_output_dimensions(cinfo); 389 390 if (cinfo->output_components != 1) /* safety check: just one component? */ 391 ERREXIT(cinfo, JERR_GIF_BUG); 392 393 /* Create decompressor output buffer. */ 394 dest->pub.buffer = (*cinfo->mem->alloc_sarray) 395 ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1); 396 dest->pub.buffer_height = 1; 397 398 return (djpeg_dest_ptr) dest; 399} 400 401#endif /* GIF_SUPPORTED */ 402