1 /* 2 * wrgif.c 3 * 4 * Copyright (C) 1991-1997, Thomas G. Lane. 5 * Modified 2015-2017 by Guido Vollbeding. 6 * This file is part of the Independent JPEG Group's software. 7 * For conditions of distribution and use, see the accompanying README file. 8 * 9 * This file contains routines to write output images in GIF format. 10 * 11 ************************************************************************** 12 * NOTE: to avoid entanglements with Unisys' patent on LZW compression, * 13 * this code has been modified to output "uncompressed GIF" files. * 14 * There is no trace of the LZW algorithm in this file. * 15 ************************************************************************** 16 * 17 * These routines may need modification for non-Unix environments or 18 * specialized applications. As they stand, they assume output to 19 * an ordinary stdio stream. 20 */ 21 22 /* 23 * This code is loosely based on ppmtogif from the PBMPLUS distribution 24 * of Feb. 1991. That file contains the following copyright notice: 25 * Based on GIFENCODE by David Rowley <mgardi@watdscu.waterloo.edu>. 26 * Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al. 27 * Copyright (C) 1989 by Jef Poskanzer. 28 * Permission to use, copy, modify, and distribute this software and its 29 * documentation for any purpose and without fee is hereby granted, provided 30 * that the above copyright notice appear in all copies and that both that 31 * copyright notice and this permission notice appear in supporting 32 * documentation. This software is provided "as is" without express or 33 * implied warranty. 34 * 35 * We are also required to state that 36 * "The Graphics Interchange Format(c) is the Copyright property of 37 * CompuServe Incorporated. GIF(sm) is a Service Mark property of 38 * CompuServe Incorporated." 39 */ 40 41 #include "cdjpeg.h" /* Common decls for cjpeg/djpeg applications */ 42 43 #ifdef GIF_SUPPORTED 44 45 46 /* Private version of data destination object */ 47 48 typedef struct { 49 struct djpeg_dest_struct pub; /* public fields */ 50 51 j_decompress_ptr cinfo; /* back link saves passing separate parm */ 52 53 /* State for packing variable-width codes into a bitstream */ 54 int n_bits; /* current number of bits/code */ 55 int maxcode; /* maximum code, given n_bits */ 56 INT32 cur_accum; /* holds bits not yet output */ 57 int cur_bits; /* # of bits in cur_accum */ 58 59 /* State for GIF code assignment */ 60 int ClearCode; /* clear code (doesn't change) */ 61 int EOFCode; /* EOF code (ditto) */ 62 int code_counter; /* counts output symbols */ 63 64 /* GIF data packet construction buffer */ 65 int bytesinpkt; /* # of bytes in current packet */ 66 char packetbuf[256]; /* workspace for accumulating packet */ 67 68 } gif_dest_struct; 69 70 typedef gif_dest_struct * gif_dest_ptr; 71 72 /* Largest value that will fit in N bits */ 73 #define MAXCODE(n_bits) ((1 << (n_bits)) - 1) 74 75 76 /* 77 * Routines to package finished data bytes into GIF data blocks. 78 * A data block consists of a count byte (1..255) and that many data bytes. 79 */ 80 81 LOCAL(void) 82 flush_packet (gif_dest_ptr dinfo) 83 /* flush any accumulated data */ 84 { 85 if (dinfo->bytesinpkt > 0) { /* never write zero-length packet */ 86 dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++; 87 if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt) 88 != (size_t) dinfo->bytesinpkt) 89 ERREXIT(dinfo->cinfo, JERR_FILE_WRITE); 90 dinfo->bytesinpkt = 0; 91 } 92 } 93 94 95 /* Add a character to current packet; flush to disk if necessary */ 96 #define CHAR_OUT(dinfo,c) \ 97 { (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c); \ 98 if ((dinfo)->bytesinpkt >= 255) \ 99 flush_packet(dinfo); \ 100 } 101 102 103 /* Routine to convert variable-width codes into a byte stream */ 104 105 LOCAL(void) 106 output (gif_dest_ptr dinfo, int code) 107 /* Emit a code of n_bits bits */ 108 /* Uses cur_accum and cur_bits to reblock into 8-bit bytes */ 109 { 110 dinfo->cur_accum |= ((INT32) code) << dinfo->cur_bits; 111 dinfo->cur_bits += dinfo->n_bits; 112 113 while (dinfo->cur_bits >= 8) { 114 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 115 dinfo->cur_accum >>= 8; 116 dinfo->cur_bits -= 8; 117 } 118 } 119 120 121 /* The pseudo-compression algorithm. 122 * 123 * In this module we simply output each pixel value as a separate symbol; 124 * thus, no compression occurs. In fact, there is expansion of one bit per 125 * pixel, because we use a symbol width one bit wider than the pixel width. 126 * 127 * GIF ordinarily uses variable-width symbols, and the decoder will expect 128 * to ratchet up the symbol width after a fixed number of symbols. 129 * To simplify the logic and keep the expansion penalty down, we emit a 130 * GIF Clear code to reset the decoder just before the width would ratchet up. 131 * Thus, all the symbols in the output file will have the same bit width. 132 * Note that emitting the Clear codes at the right times is a mere matter of 133 * counting output symbols and is in no way dependent on the LZW patent. 134 * 135 * With a small basic pixel width (low color count), Clear codes will be 136 * needed very frequently, causing the file to expand even more. So this 137 * simplistic approach wouldn't work too well on bilevel images, for example. 138 * But for output of JPEG conversions the pixel width will usually be 8 bits 139 * (129 to 256 colors), so the overhead added by Clear symbols is only about 140 * one symbol in every 256. 141 */ 142 143 LOCAL(void) 144 compress_init (gif_dest_ptr dinfo, int i_bits) 145 /* Initialize pseudo-compressor */ 146 { 147 /* init all the state variables */ 148 dinfo->n_bits = i_bits; 149 dinfo->maxcode = MAXCODE(dinfo->n_bits); 150 dinfo->ClearCode = (1 << (i_bits - 1)); 151 dinfo->EOFCode = dinfo->ClearCode + 1; 152 dinfo->code_counter = dinfo->ClearCode + 2; 153 /* init output buffering vars */ 154 dinfo->bytesinpkt = 0; 155 dinfo->cur_accum = 0; 156 dinfo->cur_bits = 0; 157 /* GIF specifies an initial Clear code */ 158 output(dinfo, dinfo->ClearCode); 159 } 160 161 162 LOCAL(void) 163 compress_pixel (gif_dest_ptr dinfo, int c) 164 /* Accept and "compress" one pixel value. 165 * The given value must be less than n_bits wide. 166 */ 167 { 168 /* Output the given pixel value as a symbol. */ 169 output(dinfo, c); 170 /* Issue Clear codes often enough to keep the reader from ratcheting up 171 * its symbol size. 172 */ 173 if (dinfo->code_counter < dinfo->maxcode) { 174 dinfo->code_counter++; 175 } else { 176 output(dinfo, dinfo->ClearCode); 177 dinfo->code_counter = dinfo->ClearCode + 2; /* reset the counter */ 178 } 179 } 180 181 182 LOCAL(void) 183 compress_term (gif_dest_ptr dinfo) 184 /* Clean up at end */ 185 { 186 /* Send an EOF code */ 187 output(dinfo, dinfo->EOFCode); 188 /* Flush the bit-packing buffer */ 189 if (dinfo->cur_bits > 0) { 190 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 191 } 192 /* Flush the packet buffer */ 193 flush_packet(dinfo); 194 } 195 196 197 /* GIF header construction */ 198 199 200 LOCAL(void) 201 put_word (gif_dest_ptr dinfo, unsigned int w) 202 /* Emit a 16-bit word, LSB first */ 203 { 204 putc(w & 0xFF, dinfo->pub.output_file); 205 putc((w >> 8) & 0xFF, dinfo->pub.output_file); 206 } 207 208 209 LOCAL(void) 210 put_3bytes (gif_dest_ptr dinfo, int val) 211 /* Emit 3 copies of same byte value --- handy subr for colormap construction */ 212 { 213 putc(val, dinfo->pub.output_file); 214 putc(val, dinfo->pub.output_file); 215 putc(val, dinfo->pub.output_file); 216 } 217 218 219 LOCAL(void) 220 emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap) 221 /* Output the GIF file header, including color map */ 222 /* If colormap==NULL, synthesize a grayscale colormap */ 223 { 224 int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte; 225 int cshift = dinfo->cinfo->data_precision - 8; 226 int i; 227 228 if (num_colors > 256) 229 ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors); 230 /* Compute bits/pixel and related values */ 231 BitsPerPixel = 1; 232 while (num_colors > (1 << BitsPerPixel)) 233 BitsPerPixel++; 234 ColorMapSize = 1 << BitsPerPixel; 235 if (BitsPerPixel <= 1) 236 InitCodeSize = 2; 237 else 238 InitCodeSize = BitsPerPixel; 239 /* 240 * Write the GIF header. 241 * Note that we generate a plain GIF87 header for maximum compatibility. 242 */ 243 putc('G', dinfo->pub.output_file); 244 putc('I', dinfo->pub.output_file); 245 putc('F', dinfo->pub.output_file); 246 putc('8', dinfo->pub.output_file); 247 putc('7', dinfo->pub.output_file); 248 putc('a', dinfo->pub.output_file); 249 /* Write the Logical Screen Descriptor */ 250 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); 251 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 252 FlagByte = 0x80; /* Yes, there is a global color table */ 253 FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */ 254 FlagByte |= (BitsPerPixel-1); /* size of global color table */ 255 putc(FlagByte, dinfo->pub.output_file); 256 putc(0, dinfo->pub.output_file); /* Background color index */ 257 putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */ 258 /* Write the Global Color Map */ 259 /* If the color map is more than 8 bits precision, */ 260 /* we reduce it to 8 bits by shifting */ 261 for (i=0; i < ColorMapSize; i++) { 262 if (i < num_colors) { 263 if (colormap != NULL) { 264 if (dinfo->cinfo->out_color_space == JCS_RGB) { 265 /* Normal case: RGB color map */ 266 putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file); 267 putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file); 268 putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file); 269 } else { 270 /* Grayscale "color map": possible if quantizing grayscale image */ 271 put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift); 272 } 273 } else { 274 /* Create a grayscale map of num_colors values, range 0..255 */ 275 put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1)); 276 } 277 } else { 278 /* fill out the map to a power of 2 */ 279 put_3bytes(dinfo, 0); 280 } 281 } 282 /* Write image separator and Image Descriptor */ 283 putc(',', dinfo->pub.output_file); /* separator */ 284 put_word(dinfo, 0); /* left/top offset */ 285 put_word(dinfo, 0); 286 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */ 287 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 288 /* flag byte: not interlaced, no local color map */ 289 putc(0x00, dinfo->pub.output_file); 290 /* Write Initial Code Size byte */ 291 putc(InitCodeSize, dinfo->pub.output_file); 292 293 /* Initialize for "compression" of image data */ 294 compress_init(dinfo, InitCodeSize+1); 295 } 296 297 298 /* 299 * Startup: write the file header. 300 */ 301 302 METHODDEF(void) 303 start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 304 { 305 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 306 307 if (cinfo->quantize_colors) 308 emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap); 309 else 310 emit_header(dest, 256, (JSAMPARRAY) NULL); 311 } 312 313 314 /* 315 * Write some pixel data. 316 * In this module rows_supplied will always be 1. 317 */ 318 319 METHODDEF(void) 320 put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo, 321 JDIMENSION rows_supplied) 322 { 323 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 324 register JSAMPROW ptr; 325 register JDIMENSION col; 326 327 ptr = dest->pub.buffer[0]; 328 for (col = cinfo->output_width; col > 0; col--) { 329 compress_pixel(dest, GETJSAMPLE(*ptr++)); 330 } 331 } 332 333 334 /* 335 * Finish up at the end of the file. 336 */ 337 338 METHODDEF(void) 339 finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 340 { 341 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 342 343 /* Flush "compression" mechanism */ 344 compress_term(dest); 345 /* Write a zero-length data block to end the series */ 346 putc(0, dest->pub.output_file); 347 /* Write the GIF terminator mark */ 348 putc(';', dest->pub.output_file); 349 /* Make sure we wrote the output file OK */ 350 JFFLUSH(dest->pub.output_file); 351 if (JFERROR(dest->pub.output_file)) 352 ERREXIT(cinfo, JERR_FILE_WRITE); 353 } 354 355 356 /* 357 * The module selection routine for GIF format output. 358 */ 359 360 GLOBAL(djpeg_dest_ptr) 361 jinit_write_gif (j_decompress_ptr cinfo) 362 { 363 gif_dest_ptr dest; 364 365 /* Create module interface object, fill in method pointers */ 366 dest = (gif_dest_ptr) 367 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 368 SIZEOF(gif_dest_struct)); 369 dest->cinfo = cinfo; /* make back link for subroutines */ 370 dest->pub.start_output = start_output_gif; 371 dest->pub.put_pixel_rows = put_pixel_rows; 372 dest->pub.finish_output = finish_output_gif; 373 374 if (cinfo->out_color_space != JCS_GRAYSCALE && 375 cinfo->out_color_space != JCS_RGB) 376 ERREXIT(cinfo, JERR_GIF_COLORSPACE); 377 378 /* Force quantization if color or if > 8 bits input */ 379 if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) { 380 /* Force quantization to at most 256 colors */ 381 cinfo->quantize_colors = TRUE; 382 if (cinfo->desired_number_of_colors > 256) 383 cinfo->desired_number_of_colors = 256; 384 } 385 386 /* Calculate output image dimensions so we can allocate space */ 387 jpeg_calc_output_dimensions(cinfo); 388 389 if (cinfo->output_components != 1) /* safety check: just one component? */ 390 ERREXIT(cinfo, JERR_GIF_BUG); 391 392 /* Create decompressor output buffer. */ 393 dest->pub.buffer = (*cinfo->mem->alloc_sarray) 394 ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1); 395 dest->pub.buffer_height = 1; 396 397 return &dest->pub; 398 } 399 400 #endif /* GIF_SUPPORTED */ 401