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 * libjpeg-turbo Modifications: 7 * Copyright (C) 2015, D. R. Commander. 8 * For conditions of distribution and use, see the accompanying README.ijg 9 * file. 10 * 11 * This file contains routines to write output images in GIF format. 12 * 13 ************************************************************************** 14 * NOTE: to avoid entanglements with Unisys' patent on LZW compression, * 15 * this code has been modified to output "uncompressed GIF" files. * 16 * There is no trace of the LZW algorithm in this file. * 17 ************************************************************************** 18 * 19 * These routines may need modification for non-Unix environments or 20 * specialized applications. As they stand, they assume output to 21 * an ordinary stdio stream. 22 */ 23 24 /* 25 * This code is loosely based on ppmtogif from the PBMPLUS distribution 26 * of Feb. 1991. That file contains the following copyright notice: 27 * Based on GIFENCODE by David Rowley <mgardi (at) watdscu.waterloo.edu>. 28 * Lempel-Ziv compression based on "compress" by Spencer W. Thomas et al. 29 * Copyright (C) 1989 by Jef Poskanzer. 30 * Permission to use, copy, modify, and distribute this software and its 31 * documentation for any purpose and without fee is hereby granted, provided 32 * that the above copyright notice appear in all copies and that both that 33 * copyright notice and this permission notice appear in supporting 34 * documentation. This software is provided "as is" without express or 35 * implied warranty. 36 * 37 * We are also required to state that 38 * "The Graphics Interchange Format(c) is the Copyright property of 39 * CompuServe Incorporated. GIF(sm) is a Service Mark property of 40 * CompuServe Incorporated." 41 */ 42 43 #include "cdjpeg.h" /* Common decls for cjpeg/djpeg applications */ 44 45 #ifdef GIF_SUPPORTED 46 47 48 /* Private version of data destination object */ 49 50 typedef struct { 51 struct djpeg_dest_struct pub; /* public fields */ 52 53 j_decompress_ptr cinfo; /* back link saves passing separate parm */ 54 55 /* State for packing variable-width codes into a bitstream */ 56 int n_bits; /* current number of bits/code */ 57 int maxcode; /* maximum code, given n_bits */ 58 long cur_accum; /* holds bits not yet output */ 59 int cur_bits; /* # of bits in cur_accum */ 60 61 /* State for GIF code assignment */ 62 int ClearCode; /* clear code (doesn't change) */ 63 int EOFCode; /* EOF code (ditto) */ 64 int code_counter; /* counts output symbols */ 65 66 /* GIF data packet construction buffer */ 67 int bytesinpkt; /* # of bytes in current packet */ 68 char packetbuf[256]; /* workspace for accumulating packet */ 69 70 } gif_dest_struct; 71 72 typedef gif_dest_struct *gif_dest_ptr; 73 74 /* Largest value that will fit in N bits */ 75 #define MAXCODE(n_bits) ((1 << (n_bits)) - 1) 76 77 78 /* 79 * Routines to package finished data bytes into GIF data blocks. 80 * A data block consists of a count byte (1..255) and that many data bytes. 81 */ 82 83 LOCAL(void) 84 flush_packet (gif_dest_ptr dinfo) 85 /* flush any accumulated data */ 86 { 87 if (dinfo->bytesinpkt > 0) { /* never write zero-length packet */ 88 dinfo->packetbuf[0] = (char) dinfo->bytesinpkt++; 89 if (JFWRITE(dinfo->pub.output_file, dinfo->packetbuf, dinfo->bytesinpkt) 90 != (size_t) dinfo->bytesinpkt) 91 ERREXIT(dinfo->cinfo, JERR_FILE_WRITE); 92 dinfo->bytesinpkt = 0; 93 } 94 } 95 96 97 /* Add a character to current packet; flush to disk if necessary */ 98 #define CHAR_OUT(dinfo,c) \ 99 { (dinfo)->packetbuf[++(dinfo)->bytesinpkt] = (char) (c); \ 100 if ((dinfo)->bytesinpkt >= 255) \ 101 flush_packet(dinfo); \ 102 } 103 104 105 /* Routine to convert variable-width codes into a byte stream */ 106 107 LOCAL(void) 108 output (gif_dest_ptr dinfo, int code) 109 /* Emit a code of n_bits bits */ 110 /* Uses cur_accum and cur_bits to reblock into 8-bit bytes */ 111 { 112 dinfo->cur_accum |= ((long) code) << dinfo->cur_bits; 113 dinfo->cur_bits += dinfo->n_bits; 114 115 while (dinfo->cur_bits >= 8) { 116 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 117 dinfo->cur_accum >>= 8; 118 dinfo->cur_bits -= 8; 119 } 120 } 121 122 123 /* The pseudo-compression algorithm. 124 * 125 * In this module we simply output each pixel value as a separate symbol; 126 * thus, no compression occurs. In fact, there is expansion of one bit per 127 * pixel, because we use a symbol width one bit wider than the pixel width. 128 * 129 * GIF ordinarily uses variable-width symbols, and the decoder will expect 130 * to ratchet up the symbol width after a fixed number of symbols. 131 * To simplify the logic and keep the expansion penalty down, we emit a 132 * GIF Clear code to reset the decoder just before the width would ratchet up. 133 * Thus, all the symbols in the output file will have the same bit width. 134 * Note that emitting the Clear codes at the right times is a mere matter of 135 * counting output symbols and is in no way dependent on the LZW patent. 136 * 137 * With a small basic pixel width (low color count), Clear codes will be 138 * needed very frequently, causing the file to expand even more. So this 139 * simplistic approach wouldn't work too well on bilevel images, for example. 140 * But for output of JPEG conversions the pixel width will usually be 8 bits 141 * (129 to 256 colors), so the overhead added by Clear symbols is only about 142 * one symbol in every 256. 143 */ 144 145 LOCAL(void) 146 compress_init (gif_dest_ptr dinfo, int i_bits) 147 /* Initialize pseudo-compressor */ 148 { 149 /* init all the state variables */ 150 dinfo->n_bits = i_bits; 151 dinfo->maxcode = MAXCODE(dinfo->n_bits); 152 dinfo->ClearCode = (1 << (i_bits - 1)); 153 dinfo->EOFCode = dinfo->ClearCode + 1; 154 dinfo->code_counter = dinfo->ClearCode + 2; 155 /* init output buffering vars */ 156 dinfo->bytesinpkt = 0; 157 dinfo->cur_accum = 0; 158 dinfo->cur_bits = 0; 159 /* GIF specifies an initial Clear code */ 160 output(dinfo, dinfo->ClearCode); 161 } 162 163 164 LOCAL(void) 165 compress_pixel (gif_dest_ptr dinfo, int c) 166 /* Accept and "compress" one pixel value. 167 * The given value must be less than n_bits wide. 168 */ 169 { 170 /* Output the given pixel value as a symbol. */ 171 output(dinfo, c); 172 /* Issue Clear codes often enough to keep the reader from ratcheting up 173 * its symbol size. 174 */ 175 if (dinfo->code_counter < dinfo->maxcode) { 176 dinfo->code_counter++; 177 } else { 178 output(dinfo, dinfo->ClearCode); 179 dinfo->code_counter = dinfo->ClearCode + 2; /* reset the counter */ 180 } 181 } 182 183 184 LOCAL(void) 185 compress_term (gif_dest_ptr dinfo) 186 /* Clean up at end */ 187 { 188 /* Send an EOF code */ 189 output(dinfo, dinfo->EOFCode); 190 /* Flush the bit-packing buffer */ 191 if (dinfo->cur_bits > 0) { 192 CHAR_OUT(dinfo, dinfo->cur_accum & 0xFF); 193 } 194 /* Flush the packet buffer */ 195 flush_packet(dinfo); 196 } 197 198 199 /* GIF header construction */ 200 201 202 LOCAL(void) 203 put_word (gif_dest_ptr dinfo, unsigned int w) 204 /* Emit a 16-bit word, LSB first */ 205 { 206 putc(w & 0xFF, dinfo->pub.output_file); 207 putc((w >> 8) & 0xFF, dinfo->pub.output_file); 208 } 209 210 211 LOCAL(void) 212 put_3bytes (gif_dest_ptr dinfo, int val) 213 /* Emit 3 copies of same byte value --- handy subr for colormap construction */ 214 { 215 putc(val, dinfo->pub.output_file); 216 putc(val, dinfo->pub.output_file); 217 putc(val, dinfo->pub.output_file); 218 } 219 220 221 LOCAL(void) 222 emit_header (gif_dest_ptr dinfo, int num_colors, JSAMPARRAY colormap) 223 /* Output the GIF file header, including color map */ 224 /* If colormap==NULL, synthesize a grayscale colormap */ 225 { 226 int BitsPerPixel, ColorMapSize, InitCodeSize, FlagByte; 227 int cshift = dinfo->cinfo->data_precision - 8; 228 int i; 229 230 if (num_colors > 256) 231 ERREXIT1(dinfo->cinfo, JERR_TOO_MANY_COLORS, num_colors); 232 /* Compute bits/pixel and related values */ 233 BitsPerPixel = 1; 234 while (num_colors > (1 << BitsPerPixel)) 235 BitsPerPixel++; 236 ColorMapSize = 1 << BitsPerPixel; 237 if (BitsPerPixel <= 1) 238 InitCodeSize = 2; 239 else 240 InitCodeSize = BitsPerPixel; 241 /* 242 * Write the GIF header. 243 * Note that we generate a plain GIF87 header for maximum compatibility. 244 */ 245 putc('G', dinfo->pub.output_file); 246 putc('I', dinfo->pub.output_file); 247 putc('F', dinfo->pub.output_file); 248 putc('8', dinfo->pub.output_file); 249 putc('7', dinfo->pub.output_file); 250 putc('a', dinfo->pub.output_file); 251 /* Write the Logical Screen Descriptor */ 252 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); 253 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 254 FlagByte = 0x80; /* Yes, there is a global color table */ 255 FlagByte |= (BitsPerPixel-1) << 4; /* color resolution */ 256 FlagByte |= (BitsPerPixel-1); /* size of global color table */ 257 putc(FlagByte, dinfo->pub.output_file); 258 putc(0, dinfo->pub.output_file); /* Background color index */ 259 putc(0, dinfo->pub.output_file); /* Reserved (aspect ratio in GIF89) */ 260 /* Write the Global Color Map */ 261 /* If the color map is more than 8 bits precision, */ 262 /* we reduce it to 8 bits by shifting */ 263 for (i=0; i < ColorMapSize; i++) { 264 if (i < num_colors) { 265 if (colormap != NULL) { 266 if (dinfo->cinfo->out_color_space == JCS_RGB) { 267 /* Normal case: RGB color map */ 268 putc(GETJSAMPLE(colormap[0][i]) >> cshift, dinfo->pub.output_file); 269 putc(GETJSAMPLE(colormap[1][i]) >> cshift, dinfo->pub.output_file); 270 putc(GETJSAMPLE(colormap[2][i]) >> cshift, dinfo->pub.output_file); 271 } else { 272 /* Grayscale "color map": possible if quantizing grayscale image */ 273 put_3bytes(dinfo, GETJSAMPLE(colormap[0][i]) >> cshift); 274 } 275 } else { 276 /* Create a grayscale map of num_colors values, range 0..255 */ 277 put_3bytes(dinfo, (i * 255 + (num_colors-1)/2) / (num_colors-1)); 278 } 279 } else { 280 /* fill out the map to a power of 2 */ 281 put_3bytes(dinfo, 0); 282 } 283 } 284 /* Write image separator and Image Descriptor */ 285 putc(',', dinfo->pub.output_file); /* separator */ 286 put_word(dinfo, 0); /* left/top offset */ 287 put_word(dinfo, 0); 288 put_word(dinfo, (unsigned int) dinfo->cinfo->output_width); /* image size */ 289 put_word(dinfo, (unsigned int) dinfo->cinfo->output_height); 290 /* flag byte: not interlaced, no local color map */ 291 putc(0x00, dinfo->pub.output_file); 292 /* Write Initial Code Size byte */ 293 putc(InitCodeSize, dinfo->pub.output_file); 294 295 /* Initialize for "compression" of image data */ 296 compress_init(dinfo, InitCodeSize+1); 297 } 298 299 300 /* 301 * Startup: write the file header. 302 */ 303 304 METHODDEF(void) 305 start_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 306 { 307 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 308 309 if (cinfo->quantize_colors) 310 emit_header(dest, cinfo->actual_number_of_colors, cinfo->colormap); 311 else 312 emit_header(dest, 256, (JSAMPARRAY) NULL); 313 } 314 315 316 /* 317 * Write some pixel data. 318 * In this module rows_supplied will always be 1. 319 */ 320 321 METHODDEF(void) 322 put_pixel_rows (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo, 323 JDIMENSION rows_supplied) 324 { 325 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 326 register JSAMPROW ptr; 327 register JDIMENSION col; 328 329 ptr = dest->pub.buffer[0]; 330 for (col = cinfo->output_width; col > 0; col--) { 331 compress_pixel(dest, GETJSAMPLE(*ptr++)); 332 } 333 } 334 335 336 /* 337 * Finish up at the end of the file. 338 */ 339 340 METHODDEF(void) 341 finish_output_gif (j_decompress_ptr cinfo, djpeg_dest_ptr dinfo) 342 { 343 gif_dest_ptr dest = (gif_dest_ptr) dinfo; 344 345 /* Flush "compression" mechanism */ 346 compress_term(dest); 347 /* Write a zero-length data block to end the series */ 348 putc(0, dest->pub.output_file); 349 /* Write the GIF terminator mark */ 350 putc(';', dest->pub.output_file); 351 /* Make sure we wrote the output file OK */ 352 fflush(dest->pub.output_file); 353 if (ferror(dest->pub.output_file)) 354 ERREXIT(cinfo, JERR_FILE_WRITE); 355 } 356 357 358 /* 359 * The module selection routine for GIF format output. 360 */ 361 362 GLOBAL(djpeg_dest_ptr) 363 jinit_write_gif (j_decompress_ptr cinfo) 364 { 365 gif_dest_ptr dest; 366 367 /* Create module interface object, fill in method pointers */ 368 dest = (gif_dest_ptr) 369 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 370 sizeof(gif_dest_struct)); 371 dest->cinfo = cinfo; /* make back link for subroutines */ 372 dest->pub.start_output = start_output_gif; 373 dest->pub.put_pixel_rows = put_pixel_rows; 374 dest->pub.finish_output = finish_output_gif; 375 376 if (cinfo->out_color_space != JCS_GRAYSCALE && 377 cinfo->out_color_space != JCS_RGB) 378 ERREXIT(cinfo, JERR_GIF_COLORSPACE); 379 380 /* Force quantization if color or if > 8 bits input */ 381 if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) { 382 /* Force quantization to at most 256 colors */ 383 cinfo->quantize_colors = TRUE; 384 if (cinfo->desired_number_of_colors > 256) 385 cinfo->desired_number_of_colors = 256; 386 } 387 388 /* Calculate output image dimensions so we can allocate space */ 389 jpeg_calc_output_dimensions(cinfo); 390 391 if (cinfo->output_components != 1) /* safety check: just one component? */ 392 ERREXIT(cinfo, JERR_GIF_BUG); 393 394 /* Create decompressor output buffer. */ 395 dest->pub.buffer = (*cinfo->mem->alloc_sarray) 396 ((j_common_ptr) cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION) 1); 397 dest->pub.buffer_height = 1; 398 399 return (djpeg_dest_ptr) dest; 400 } 401 402 #endif /* GIF_SUPPORTED */ 403
