Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

497 lines (419 sloc) 13.879 kb
/*
* rdjpgcom.c
*
* Copyright (C) 1994-1997, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains a very simple stand-alone application that displays
* the text in COM (comment) markers in a JFIF file.
* This may be useful as an example of the minimum logic needed to parse
* JPEG markers.
*/
#define JPEG_CJPEG_DJPEG /* to get the command-line config symbols */
#include "jinclude.h" /* get auto-config symbols, <stdio.h> */
#include <ctype.h> /* to declare isupper(), tolower() */
#ifdef USE_SETMODE
#include <fcntl.h> /* to declare setmode()'s parameter macros */
/* If you have setmode() but not <io.h>, just delete this line: */
#include <io.h> /* to declare setmode() */
#endif
#ifdef USE_CCOMMAND /* command-line reader for Macintosh */
#ifdef __MWERKS__
#include <SIOUX.h> /* Metrowerks needs this */
#include <console.h> /* ... and this */
#endif
#ifdef THINK_C
#include <console.h> /* Think declares it here */
#endif
#endif
#ifdef DONT_USE_B_MODE /* define mode parameters for fopen() */
#define READ_BINARY "r"
#else
#ifdef VMS /* VMS is very nonstandard */
#define READ_BINARY "rb", "ctx=stm"
#else /* standard ANSI-compliant case */
#define READ_BINARY "rb"
#endif
#endif
#ifndef EXIT_FAILURE /* define exit() codes if not provided */
#define EXIT_FAILURE 1
#endif
#ifndef EXIT_SUCCESS
#ifdef VMS
#define EXIT_SUCCESS 1 /* VMS is very nonstandard */
#else
#define EXIT_SUCCESS 0
#endif
#endif
/*
* These macros are used to read the input file.
* To reuse this code in another application, you might need to change these.
*/
static FILE * infile; /* input JPEG file */
/* Return next input byte, or EOF if no more */
#define NEXTBYTE() getc(infile)
/* Error exit handler */
#define ERREXIT(msg) (fprintf(stderr, "%s\n", msg), exit(EXIT_FAILURE))
/* Read one byte, testing for EOF */
static int
read_1_byte (void)
{
int c;
c = NEXTBYTE();
if (c == EOF)
ERREXIT("Premature EOF in JPEG file");
return c;
}
/* Read 2 bytes, convert to unsigned int */
/* All 2-byte quantities in JPEG markers are MSB first */
static unsigned int
read_2_bytes (void)
{
int c1, c2;
c1 = NEXTBYTE();
if (c1 == EOF)
ERREXIT("Premature EOF in JPEG file");
c2 = NEXTBYTE();
if (c2 == EOF)
ERREXIT("Premature EOF in JPEG file");
return (((unsigned int) c1) << 8) + ((unsigned int) c2);
}
/*
* JPEG markers consist of one or more 0xFF bytes, followed by a marker
* code byte (which is not an FF). Here are the marker codes of interest
* in this program. (See jdmarker.c for a more complete list.)
*/
#define M_SOF0 0xC0 /* Start Of Frame N */
#define M_SOF1 0xC1 /* N indicates which compression process */
#define M_SOF2 0xC2 /* Only SOF0-SOF2 are now in common use */
#define M_SOF3 0xC3
#define M_SOF5 0xC5 /* NB: codes C4 and CC are NOT SOF markers */
#define M_SOF6 0xC6
#define M_SOF7 0xC7
#define M_SOF9 0xC9
#define M_SOF10 0xCA
#define M_SOF11 0xCB
#define M_SOF13 0xCD
#define M_SOF14 0xCE
#define M_SOF15 0xCF
#define M_SOI 0xD8 /* Start Of Image (beginning of datastream) */
#define M_EOI 0xD9 /* End Of Image (end of datastream) */
#define M_SOS 0xDA /* Start Of Scan (begins compressed data) */
#define M_APP0 0xE0 /* Application-specific marker, type N */
#define M_APP12 0xEC /* (we don't bother to list all 16 APPn's) */
#define M_COM 0xFE /* COMment */
/*
* Find the next JPEG marker and return its marker code.
* We expect at least one FF byte, possibly more if the compressor used FFs
* to pad the file.
* There could also be non-FF garbage between markers. The treatment of such
* garbage is unspecified; we choose to skip over it but emit a warning msg.
* NB: this routine must not be used after seeing SOS marker, since it will
* not deal correctly with FF/00 sequences in the compressed image data...
*/
static int
next_marker (void)
{
int c;
int discarded_bytes = 0;
/* Find 0xFF byte; count and skip any non-FFs. */
c = read_1_byte();
while (c != 0xFF) {
discarded_bytes++;
c = read_1_byte();
}
/* Get marker code byte, swallowing any duplicate FF bytes. Extra FFs
* are legal as pad bytes, so don't count them in discarded_bytes.
*/
do {
c = read_1_byte();
} while (c == 0xFF);
if (discarded_bytes != 0) {
fprintf(stderr, "Warning: garbage data found in JPEG file\n");
}
return c;
}
/*
* Read the initial marker, which should be SOI.
* For a JFIF file, the first two bytes of the file should be literally
* 0xFF M_SOI. To be more general, we could use next_marker, but if the
* input file weren't actually JPEG at all, next_marker might read the whole
* file and then return a misleading error message...
*/
static int
first_marker (void)
{
int c1, c2;
c1 = NEXTBYTE();
c2 = NEXTBYTE();
if (c1 != 0xFF || c2 != M_SOI)
ERREXIT("Not a JPEG file");
return c2;
}
/*
* Most types of marker are followed by a variable-length parameter segment.
* This routine skips over the parameters for any marker we don't otherwise
* want to process.
* Note that we MUST skip the parameter segment explicitly in order not to
* be fooled by 0xFF bytes that might appear within the parameter segment;
* such bytes do NOT introduce new markers.
*/
static void
skip_variable (void)
/* Skip over an unknown or uninteresting variable-length marker */
{
unsigned int length;
/* Get the marker parameter length count */
length = read_2_bytes();
/* Length includes itself, so must be at least 2 */
if (length < 2)
ERREXIT("Erroneous JPEG marker length");
length -= 2;
/* Skip over the remaining bytes */
while (length > 0) {
(void) read_1_byte();
length--;
}
}
/*
* Process a COM marker.
* We want to print out the marker contents as legible text;
* we must guard against non-text junk and varying newline representations.
*/
static void
process_COM (void)
{
unsigned int length;
int ch;
int lastch = 0;
/* Get the marker parameter length count */
length = read_2_bytes();
/* Length includes itself, so must be at least 2 */
if (length < 2)
ERREXIT("Erroneous JPEG marker length");
length -= 2;
while (length > 0) {
ch = read_1_byte();
/* Emit the character in a readable form.
* Nonprintables are converted to \nnn form,
* while \ is converted to \\.
* Newlines in CR, CR/LF, or LF form will be printed as one newline.
*/
if (ch == '\r') {
printf("\n");
} else if (ch == '\n') {
if (lastch != '\r')
printf("\n");
} else if (ch == '\\') {
printf("\\\\");
} else if (isprint(ch)) {
putc(ch, stdout);
} else {
printf("\\%03o", ch);
}
lastch = ch;
length--;
}
printf("\n");
}
/*
* Process a SOFn marker.
* This code is only needed if you want to know the image dimensions...
*/
static void
process_SOFn (int marker)
{
unsigned int length;
unsigned int image_height, image_width;
int data_precision, num_components;
const char * process;
int ci;
length = read_2_bytes(); /* usual parameter length count */
data_precision = read_1_byte();
image_height = read_2_bytes();
image_width = read_2_bytes();
num_components = read_1_byte();
switch (marker) {
case M_SOF0: process = "Baseline"; break;
case M_SOF1: process = "Extended sequential"; break;
case M_SOF2: process = "Progressive"; break;
case M_SOF3: process = "Lossless"; break;
case M_SOF5: process = "Differential sequential"; break;
case M_SOF6: process = "Differential progressive"; break;
case M_SOF7: process = "Differential lossless"; break;
case M_SOF9: process = "Extended sequential, arithmetic coding"; break;
case M_SOF10: process = "Progressive, arithmetic coding"; break;
case M_SOF11: process = "Lossless, arithmetic coding"; break;
case M_SOF13: process = "Differential sequential, arithmetic coding"; break;
case M_SOF14: process = "Differential progressive, arithmetic coding"; break;
case M_SOF15: process = "Differential lossless, arithmetic coding"; break;
default: process = "Unknown"; break;
}
printf("JPEG image is %uw * %uh, %d color components, %d bits per sample\n",
image_width, image_height, num_components, data_precision);
printf("JPEG process: %s\n", process);
if (length != (unsigned int) (8 + num_components * 3))
ERREXIT("Bogus SOF marker length");
for (ci = 0; ci < num_components; ci++) {
(void) read_1_byte(); /* Component ID code */
(void) read_1_byte(); /* H, V sampling factors */
(void) read_1_byte(); /* Quantization table number */
}
}
/*
* Parse the marker stream until SOS or EOI is seen;
* display any COM markers.
* While the companion program wrjpgcom will always insert COM markers before
* SOFn, other implementations might not, so we scan to SOS before stopping.
* If we were only interested in the image dimensions, we would stop at SOFn.
* (Conversely, if we only cared about COM markers, there would be no need
* for special code to handle SOFn; we could treat it like other markers.)
*/
static int
scan_JPEG_header (int verbose)
{
int marker;
/* Expect SOI at start of file */
if (first_marker() != M_SOI)
ERREXIT("Expected SOI marker first");
/* Scan miscellaneous markers until we reach SOS. */
for (;;) {
marker = next_marker();
switch (marker) {
/* Note that marker codes 0xC4, 0xC8, 0xCC are not, and must not be,
* treated as SOFn. C4 in particular is actually DHT.
*/
case M_SOF0: /* Baseline */
case M_SOF1: /* Extended sequential, Huffman */
case M_SOF2: /* Progressive, Huffman */
case M_SOF3: /* Lossless, Huffman */
case M_SOF5: /* Differential sequential, Huffman */
case M_SOF6: /* Differential progressive, Huffman */
case M_SOF7: /* Differential lossless, Huffman */
case M_SOF9: /* Extended sequential, arithmetic */
case M_SOF10: /* Progressive, arithmetic */
case M_SOF11: /* Lossless, arithmetic */
case M_SOF13: /* Differential sequential, arithmetic */
case M_SOF14: /* Differential progressive, arithmetic */
case M_SOF15: /* Differential lossless, arithmetic */
if (verbose)
process_SOFn(marker);
else
skip_variable();
break;
case M_SOS: /* stop before hitting compressed data */
return marker;
case M_EOI: /* in case it's a tables-only JPEG stream */
return marker;
case M_COM:
process_COM();
break;
case M_APP12:
/* Some digital camera makers put useful textual information into
* APP12 markers, so we print those out too when in -verbose mode.
*/
if (verbose) {
printf("APP12 contains:\n");
process_COM();
} else
skip_variable();
break;
default: /* Anything else just gets skipped */
skip_variable(); /* we assume it has a parameter count... */
break;
}
} /* end loop */
}
/* Command line parsing code */
static const char * progname; /* program name for error messages */
static void
usage (void)
/* complain about bad command line */
{
fprintf(stderr, "rdjpgcom displays any textual comments in a JPEG file.\n");
fprintf(stderr, "Usage: %s [switches] [inputfile]\n", progname);
fprintf(stderr, "Switches (names may be abbreviated):\n");
fprintf(stderr, " -verbose Also display dimensions of JPEG image\n");
exit(EXIT_FAILURE);
}
static int
keymatch (char * arg, const char * keyword, int minchars)
/* Case-insensitive matching of (possibly abbreviated) keyword switches. */
/* keyword is the constant keyword (must be lower case already), */
/* minchars is length of minimum legal abbreviation. */
{
register int ca, ck;
register int nmatched = 0;
while ((ca = *arg++) != '\0') {
if ((ck = *keyword++) == '\0')
return 0; /* arg longer than keyword, no good */
if (isupper(ca)) /* force arg to lcase (assume ck is already) */
ca = tolower(ca);
if (ca != ck)
return 0; /* no good */
nmatched++; /* count matched characters */
}
/* reached end of argument; fail if it's too short for unique abbrev */
if (nmatched < minchars)
return 0;
return 1; /* A-OK */
}
/*
* The main program.
*/
int
main (int argc, char **argv)
{
int argn;
char * arg;
int verbose = 0;
/* On Mac, fetch a command line. */
#ifdef USE_CCOMMAND
argc = ccommand(&argv);
#endif
progname = argv[0];
if (progname == NULL || progname[0] == 0)
progname = "rdjpgcom"; /* in case C library doesn't provide it */
/* Parse switches, if any */
for (argn = 1; argn < argc; argn++) {
arg = argv[argn];
if (arg[0] != '-')
break; /* not switch, must be file name */
arg++; /* advance over '-' */
if (keymatch(arg, "verbose", 1)) {
verbose++;
} else
usage();
}
/* Open the input file. */
/* Unix style: expect zero or one file name */
if (argn < argc-1) {
fprintf(stderr, "%s: only one input file\n", progname);
usage();
}
if (argn < argc) {
if ((infile = fopen(argv[argn], READ_BINARY)) == NULL) {
fprintf(stderr, "%s: can't open %s\n", progname, argv[argn]);
exit(EXIT_FAILURE);
}
} else {
/* default input file is stdin */
#ifdef USE_SETMODE /* need to hack file mode? */
setmode(fileno(stdin), O_BINARY);
#endif
#ifdef USE_FDOPEN /* need to re-open in binary mode? */
if ((infile = fdopen(fileno(stdin), READ_BINARY)) == NULL) {
fprintf(stderr, "%s: can't open stdin\n", progname);
exit(EXIT_FAILURE);
}
#else
infile = stdin;
#endif
}
/* Scan the JPEG headers. */
(void) scan_JPEG_header(verbose);
/* All done. */
exit(EXIT_SUCCESS);
return 0; /* suppress no-return-value warnings */
}
Jump to Line
Something went wrong with that request. Please try again.