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@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)
flush_packet(gif_dest_ptr dinfo)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)
output(gif_dest_ptr dinfo,int code)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)
compress_init(gif_dest_ptr dinfo,int i_bits)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)
compress_pixel(gif_dest_ptr dinfo,int c)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)
compress_term(gif_dest_ptr dinfo)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)
put_word(gif_dest_ptr dinfo,unsigned int w)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)
put_3bytes(gif_dest_ptr dinfo,int val)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)
emit_header(gif_dest_ptr dinfo,int num_colors,JSAMPARRAY colormap)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)
start_output_gif(j_decompress_ptr cinfo,djpeg_dest_ptr dinfo)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)
put_pixel_rows(j_decompress_ptr cinfo,djpeg_dest_ptr dinfo,JDIMENSION rows_supplied)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)
finish_output_gif(j_decompress_ptr cinfo,djpeg_dest_ptr dinfo)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)
jinit_write_gif(j_decompress_ptr cinfo)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