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, 2017, 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@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)
flush_packet(gif_dest_ptr dinfo)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)
output(gif_dest_ptr dinfo,int code)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)
compress_init(gif_dest_ptr dinfo,int i_bits)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)
compress_pixel(gif_dest_ptr dinfo,int c)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)
compress_term(gif_dest_ptr dinfo)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)
put_word(gif_dest_ptr dinfo,unsigned int w)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)
put_3bytes(gif_dest_ptr dinfo,int val)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)
emit_header(gif_dest_ptr dinfo,int num_colors,JSAMPARRAY colormap)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)
start_output_gif(j_decompress_ptr cinfo,djpeg_dest_ptr dinfo)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)
put_pixel_rows(j_decompress_ptr cinfo,djpeg_dest_ptr dinfo,JDIMENSION rows_supplied)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)
finish_output_gif(j_decompress_ptr cinfo,djpeg_dest_ptr dinfo)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 * Re-calculate buffer dimensions based on output dimensions.
360 */
361
362 METHODDEF(void)
calc_buffer_dimensions_gif(j_decompress_ptr cinfo,djpeg_dest_ptr dinfo)363 calc_buffer_dimensions_gif(j_decompress_ptr cinfo, djpeg_dest_ptr dinfo)
364 {
365 }
366
367
368 /*
369 * The module selection routine for GIF format output.
370 */
371
372 GLOBAL(djpeg_dest_ptr)
jinit_write_gif(j_decompress_ptr cinfo)373 jinit_write_gif(j_decompress_ptr cinfo)
374 {
375 gif_dest_ptr dest;
376
377 /* Create module interface object, fill in method pointers */
378 dest = (gif_dest_ptr)
379 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
380 sizeof(gif_dest_struct));
381 dest->cinfo = cinfo; /* make back link for subroutines */
382 dest->pub.start_output = start_output_gif;
383 dest->pub.put_pixel_rows = put_pixel_rows;
384 dest->pub.finish_output = finish_output_gif;
385 dest->pub.calc_buffer_dimensions = calc_buffer_dimensions_gif;
386
387 if (cinfo->out_color_space != JCS_GRAYSCALE &&
388 cinfo->out_color_space != JCS_RGB)
389 ERREXIT(cinfo, JERR_GIF_COLORSPACE);
390
391 /* Force quantization if color or if > 8 bits input */
392 if (cinfo->out_color_space != JCS_GRAYSCALE || cinfo->data_precision > 8) {
393 /* Force quantization to at most 256 colors */
394 cinfo->quantize_colors = TRUE;
395 if (cinfo->desired_number_of_colors > 256)
396 cinfo->desired_number_of_colors = 256;
397 }
398
399 /* Calculate output image dimensions so we can allocate space */
400 jpeg_calc_output_dimensions(cinfo);
401
402 if (cinfo->output_components != 1) /* safety check: just one component? */
403 ERREXIT(cinfo, JERR_GIF_BUG);
404
405 /* Create decompressor output buffer. */
406 dest->pub.buffer = (*cinfo->mem->alloc_sarray)
407 ((j_common_ptr)cinfo, JPOOL_IMAGE, cinfo->output_width, (JDIMENSION)1);
408 dest->pub.buffer_height = 1;
409
410 return (djpeg_dest_ptr)dest;
411 }
412
413 #endif /* GIF_SUPPORTED */
414