rdjpgcom.c revision 9f5d49a1588e438ae7ceabd0c94172117e3303aa 
1/*
2 * rdjpgcom.c
3 *
4 * Copyright (C) 1994-1997, 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 a very simple stand-alone application that displays
9 * the text in COM (comment) markers in a JFIF file.
10 * This may be useful as an example of the minimum logic needed to parse
11 * JPEG markers.
12 */
13
14#define JPEG_CJPEG_DJPEG	/* to get the command-line config symbols */
15#include "jinclude.h"		/* get auto-config symbols, <stdio.h> */
16
17#include <ctype.h>		/* to declare isupper(), tolower() */
18#ifdef USE_SETMODE
19#include <fcntl.h>		/* to declare setmode()'s parameter macros */
20/* If you have setmode() but not <io.h>, just delete this line: */
21#include <io.h>			/* to declare setmode() */
22#endif
23
24#ifdef USE_CCOMMAND		/* command-line reader for Macintosh */
25#ifdef __MWERKS__
26#include <SIOUX.h>              /* Metrowerks needs this */
27#include <console.h>		/* ... and this */
28#endif
29#ifdef THINK_C
30#include <console.h>		/* Think declares it here */
31#endif
32#endif
33
34#ifdef DONT_USE_B_MODE		/* define mode parameters for fopen() */
35#define READ_BINARY	"r"
36#else
37#ifdef VMS			/* VMS is very nonstandard */
38#define READ_BINARY	"rb", "ctx=stm"
39#else				/* standard ANSI-compliant case */
40#define READ_BINARY	"rb"
41#endif
42#endif
43
44#ifndef EXIT_FAILURE		/* define exit() codes if not provided */
45#define EXIT_FAILURE  1
46#endif
47#ifndef EXIT_SUCCESS
48#ifdef VMS
49#define EXIT_SUCCESS  1		/* VMS is very nonstandard */
50#else
51#define EXIT_SUCCESS  0
52#endif
53#endif
54
55
56/*
57 * These macros are used to read the input file.
58 * To reuse this code in another application, you might need to change these.
59 */
60
61static FILE * infile;		/* input JPEG file */
62
63/* Return next input byte, or EOF if no more */
64#define NEXTBYTE()  getc(infile)
65
66
67/* Error exit handler */
68#define ERREXIT(msg)  (fprintf(stderr, "%s\n", msg), exit(EXIT_FAILURE))
69
70
71/* Read one byte, testing for EOF */
72static int
73read_1_byte (void)
74{
75  int c;
76
77  c = NEXTBYTE();
78  if (c == EOF)
79    ERREXIT("Premature EOF in JPEG file");
80  return c;
81}
82
83/* Read 2 bytes, convert to unsigned int */
84/* All 2-byte quantities in JPEG markers are MSB first */
85static unsigned int
86read_2_bytes (void)
87{
88  int c1, c2;
89
90  c1 = NEXTBYTE();
91  if (c1 == EOF)
92    ERREXIT("Premature EOF in JPEG file");
93  c2 = NEXTBYTE();
94  if (c2 == EOF)
95    ERREXIT("Premature EOF in JPEG file");
96  return (((unsigned int) c1) << 8) + ((unsigned int) c2);
97}
98
99
100/*
101 * JPEG markers consist of one or more 0xFF bytes, followed by a marker
102 * code byte (which is not an FF).  Here are the marker codes of interest
103 * in this program.  (See jdmarker.c for a more complete list.)
104 */
105
106#define M_SOF0  0xC0		/* Start Of Frame N */
107#define M_SOF1  0xC1		/* N indicates which compression process */
108#define M_SOF2  0xC2		/* Only SOF0-SOF2 are now in common use */
109#define M_SOF3  0xC3
110#define M_SOF5  0xC5		/* NB: codes C4 and CC are NOT SOF markers */
111#define M_SOF6  0xC6
112#define M_SOF7  0xC7
113#define M_SOF9  0xC9
114#define M_SOF10 0xCA
115#define M_SOF11 0xCB
116#define M_SOF13 0xCD
117#define M_SOF14 0xCE
118#define M_SOF15 0xCF
119#define M_SOI   0xD8		/* Start Of Image (beginning of datastream) */
120#define M_EOI   0xD9		/* End Of Image (end of datastream) */
121#define M_SOS   0xDA		/* Start Of Scan (begins compressed data) */
122#define M_APP0	0xE0		/* Application-specific marker, type N */
123#define M_APP12	0xEC		/* (we don't bother to list all 16 APPn's) */
124#define M_COM   0xFE		/* COMment */
125
126
127/*
128 * Find the next JPEG marker and return its marker code.
129 * We expect at least one FF byte, possibly more if the compressor used FFs
130 * to pad the file.
131 * There could also be non-FF garbage between markers.  The treatment of such
132 * garbage is unspecified; we choose to skip over it but emit a warning msg.
133 * NB: this routine must not be used after seeing SOS marker, since it will
134 * not deal correctly with FF/00 sequences in the compressed image data...
135 */
136
137static int
138next_marker (void)
139{
140  int c;
141  int discarded_bytes = 0;
142
143  /* Find 0xFF byte; count and skip any non-FFs. */
144  c = read_1_byte();
145  while (c != 0xFF) {
146    discarded_bytes++;
147    c = read_1_byte();
148  }
149  /* Get marker code byte, swallowing any duplicate FF bytes.  Extra FFs
150   * are legal as pad bytes, so don't count them in discarded_bytes.
151   */
152  do {
153    c = read_1_byte();
154  } while (c == 0xFF);
155
156  if (discarded_bytes != 0) {
157    fprintf(stderr, "Warning: garbage data found in JPEG file\n");
158  }
159
160  return c;
161}
162
163
164/*
165 * Read the initial marker, which should be SOI.
166 * For a JFIF file, the first two bytes of the file should be literally
167 * 0xFF M_SOI.  To be more general, we could use next_marker, but if the
168 * input file weren't actually JPEG at all, next_marker might read the whole
169 * file and then return a misleading error message...
170 */
171
172static int
173first_marker (void)
174{
175  int c1, c2;
176
177  c1 = NEXTBYTE();
178  c2 = NEXTBYTE();
179  if (c1 != 0xFF || c2 != M_SOI)
180    ERREXIT("Not a JPEG file");
181  return c2;
182}
183
184
185/*
186 * Most types of marker are followed by a variable-length parameter segment.
187 * This routine skips over the parameters for any marker we don't otherwise
188 * want to process.
189 * Note that we MUST skip the parameter segment explicitly in order not to
190 * be fooled by 0xFF bytes that might appear within the parameter segment;
191 * such bytes do NOT introduce new markers.
192 */
193
194static void
195skip_variable (void)
196/* Skip over an unknown or uninteresting variable-length marker */
197{
198  unsigned int length;
199
200  /* Get the marker parameter length count */
201  length = read_2_bytes();
202  /* Length includes itself, so must be at least 2 */
203  if (length < 2)
204    ERREXIT("Erroneous JPEG marker length");
205  length -= 2;
206  /* Skip over the remaining bytes */
207  while (length > 0) {
208    (void) read_1_byte();
209    length--;
210  }
211}
212
213
214/*
215 * Process a COM marker.
216 * We want to print out the marker contents as legible text;
217 * we must guard against non-text junk and varying newline representations.
218 */
219
220static void
221process_COM (void)
222{
223  unsigned int length;
224  int ch;
225  int lastch = 0;
226
227  /* Get the marker parameter length count */
228  length = read_2_bytes();
229  /* Length includes itself, so must be at least 2 */
230  if (length < 2)
231    ERREXIT("Erroneous JPEG marker length");
232  length -= 2;
233
234  while (length > 0) {
235    ch = read_1_byte();
236    /* Emit the character in a readable form.
237     * Nonprintables are converted to \nnn form,
238     * while \ is converted to \\.
239     * Newlines in CR, CR/LF, or LF form will be printed as one newline.
240     */
241    if (ch == '\r') {
242      printf("\n");
243    } else if (ch == '\n') {
244      if (lastch != '\r')
245	printf("\n");
246    } else if (ch == '\\') {
247      printf("\\\\");
248    } else if (isprint(ch)) {
249      putc(ch, stdout);
250    } else {
251      printf("\\%03o", ch);
252    }
253    lastch = ch;
254    length--;
255  }
256  printf("\n");
257}
258
259
260/*
261 * Process a SOFn marker.
262 * This code is only needed if you want to know the image dimensions...
263 */
264
265static void
266process_SOFn (int marker)
267{
268  unsigned int length;
269  unsigned int image_height, image_width;
270  int data_precision, num_components;
271  const char * process;
272  int ci;
273
274  length = read_2_bytes();	/* usual parameter length count */
275
276  data_precision = read_1_byte();
277  image_height = read_2_bytes();
278  image_width = read_2_bytes();
279  num_components = read_1_byte();
280
281  switch (marker) {
282  case M_SOF0:	process = "Baseline";  break;
283  case M_SOF1:	process = "Extended sequential";  break;
284  case M_SOF2:	process = "Progressive";  break;
285  case M_SOF3:	process = "Lossless";  break;
286  case M_SOF5:	process = "Differential sequential";  break;
287  case M_SOF6:	process = "Differential progressive";  break;
288  case M_SOF7:	process = "Differential lossless";  break;
289  case M_SOF9:	process = "Extended sequential, arithmetic coding";  break;
290  case M_SOF10:	process = "Progressive, arithmetic coding";  break;
291  case M_SOF11:	process = "Lossless, arithmetic coding";  break;
292  case M_SOF13:	process = "Differential sequential, arithmetic coding";  break;
293  case M_SOF14:	process = "Differential progressive, arithmetic coding"; break;
294  case M_SOF15:	process = "Differential lossless, arithmetic coding";  break;
295  default:	process = "Unknown";  break;
296  }
297
298  printf("JPEG image is %uw * %uh, %d color components, %d bits per sample\n",
299	 image_width, image_height, num_components, data_precision);
300  printf("JPEG process: %s\n", process);
301
302  if (length != (unsigned int) (8 + num_components * 3))
303    ERREXIT("Bogus SOF marker length");
304
305  for (ci = 0; ci < num_components; ci++) {
306    (void) read_1_byte();	/* Component ID code */
307    (void) read_1_byte();	/* H, V sampling factors */
308    (void) read_1_byte();	/* Quantization table number */
309  }
310}
311
312
313/*
314 * Parse the marker stream until SOS or EOI is seen;
315 * display any COM markers.
316 * While the companion program wrjpgcom will always insert COM markers before
317 * SOFn, other implementations might not, so we scan to SOS before stopping.
318 * If we were only interested in the image dimensions, we would stop at SOFn.
319 * (Conversely, if we only cared about COM markers, there would be no need
320 * for special code to handle SOFn; we could treat it like other markers.)
321 */
322
323static int
324scan_JPEG_header (int verbose)
325{
326  int marker;
327
328  /* Expect SOI at start of file */
329  if (first_marker() != M_SOI)
330    ERREXIT("Expected SOI marker first");
331
332  /* Scan miscellaneous markers until we reach SOS. */
333  for (;;) {
334    marker = next_marker();
335    switch (marker) {
336      /* Note that marker codes 0xC4, 0xC8, 0xCC are not, and must not be,
337       * treated as SOFn.  C4 in particular is actually DHT.
338       */
339    case M_SOF0:		/* Baseline */
340    case M_SOF1:		/* Extended sequential, Huffman */
341    case M_SOF2:		/* Progressive, Huffman */
342    case M_SOF3:		/* Lossless, Huffman */
343    case M_SOF5:		/* Differential sequential, Huffman */
344    case M_SOF6:		/* Differential progressive, Huffman */
345    case M_SOF7:		/* Differential lossless, Huffman */
346    case M_SOF9:		/* Extended sequential, arithmetic */
347    case M_SOF10:		/* Progressive, arithmetic */
348    case M_SOF11:		/* Lossless, arithmetic */
349    case M_SOF13:		/* Differential sequential, arithmetic */
350    case M_SOF14:		/* Differential progressive, arithmetic */
351    case M_SOF15:		/* Differential lossless, arithmetic */
352      if (verbose)
353	process_SOFn(marker);
354      else
355	skip_variable();
356      break;
357
358    case M_SOS:			/* stop before hitting compressed data */
359      return marker;
360
361    case M_EOI:			/* in case it's a tables-only JPEG stream */
362      return marker;
363
364    case M_COM:
365      process_COM();
366      break;
367
368    case M_APP12:
369      /* Some digital camera makers put useful textual information into
370       * APP12 markers, so we print those out too when in -verbose mode.
371       */
372      if (verbose) {
373	printf("APP12 contains:\n");
374	process_COM();
375      } else
376	skip_variable();
377      break;
378
379    default:			/* Anything else just gets skipped */
380      skip_variable();		/* we assume it has a parameter count... */
381      break;
382    }
383  } /* end loop */
384}
385
386
387/* Command line parsing code */
388
389static const char * progname;	/* program name for error messages */
390
391
392static void
393usage (void)
394/* complain about bad command line */
395{
396  fprintf(stderr, "rdjpgcom displays any textual comments in a JPEG file.\n");
397
398  fprintf(stderr, "Usage: %s [switches] [inputfile]\n", progname);
399
400  fprintf(stderr, "Switches (names may be abbreviated):\n");
401  fprintf(stderr, "  -verbose    Also display dimensions of JPEG image\n");
402
403  exit(EXIT_FAILURE);
404}
405
406
407static int
408keymatch (char * arg, const char * keyword, int minchars)
409/* Case-insensitive matching of (possibly abbreviated) keyword switches. */
410/* keyword is the constant keyword (must be lower case already), */
411/* minchars is length of minimum legal abbreviation. */
412{
413  register int ca, ck;
414  register int nmatched = 0;
415
416  while ((ca = *arg++) != '\0') {
417    if ((ck = *keyword++) == '\0')
418      return 0;			/* arg longer than keyword, no good */
419    if (isupper(ca))		/* force arg to lcase (assume ck is already) */
420      ca = tolower(ca);
421    if (ca != ck)
422      return 0;			/* no good */
423    nmatched++;			/* count matched characters */
424  }
425  /* reached end of argument; fail if it's too short for unique abbrev */
426  if (nmatched < minchars)
427    return 0;
428  return 1;			/* A-OK */
429}
430
431
432/*
433 * The main program.
434 */
435
436int
437main (int argc, char **argv)
438{
439  int argn;
440  char * arg;
441  int verbose = 0;
442
443  /* On Mac, fetch a command line. */
444#ifdef USE_CCOMMAND
445  argc = ccommand(&argv);
446#endif
447
448  progname = argv[0];
449  if (progname == NULL || progname[0] == 0)
450    progname = "rdjpgcom";	/* in case C library doesn't provide it */
451
452  /* Parse switches, if any */
453  for (argn = 1; argn < argc; argn++) {
454    arg = argv[argn];
455    if (arg[0] != '-')
456      break;			/* not switch, must be file name */
457    arg++;			/* advance over '-' */
458    if (keymatch(arg, "verbose", 1)) {
459      verbose++;
460    } else
461      usage();
462  }
463
464  /* Open the input file. */
465  /* Unix style: expect zero or one file name */
466  if (argn < argc-1) {
467    fprintf(stderr, "%s: only one input file\n", progname);
468    usage();
469  }
470  if (argn < argc) {
471    if ((infile = fopen(argv[argn], READ_BINARY)) == NULL) {
472      fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
473      exit(EXIT_FAILURE);
474    }
475  } else {
476    /* default input file is stdin */
477#ifdef USE_SETMODE		/* need to hack file mode? */
478    setmode(fileno(stdin), O_BINARY);
479#endif
480#ifdef USE_FDOPEN		/* need to re-open in binary mode? */
481    if ((infile = fdopen(fileno(stdin), READ_BINARY)) == NULL) {
482      fprintf(stderr, "%s: can't open stdin\n", progname);
483      exit(EXIT_FAILURE);
484    }
485#else
486    infile = stdin;
487#endif
488  }
489
490  /* Scan the JPEG headers. */
491  (void) scan_JPEG_header(verbose);
492
493  /* All done. */
494  exit(EXIT_SUCCESS);
495  return 0;			/* suppress no-return-value warnings */
496}
497