root/rdjpgcom.c
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DEFINITIONS
This source file includes following definitions.
- read_1_byte
- read_2_bytes
- next_marker
- first_marker
- skip_variable
- process_COM
- process_SOFn
- scan_JPEG_header
- usage
- keymatch
- main
/*
* rdjpgcom.c
*
* Copyright (C) 1994-1997, Thomas G. Lane.
* Modified 2009 by Bill Allombert, Guido Vollbeding.
* 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> */
#ifdef HAVE_LOCALE_H
#include <locale.h> /* Bill Allombert: use locale for isprint */
#endif
#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 (int raw)
{
unsigned int length;
int ch;
int lastch = 0;
/* Bill Allombert: set locale properly for isprint */
#ifdef HAVE_LOCALE_H
setlocale(LC_CTYPE, "");
#endif
/* 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();
if (raw) {
putc(ch, stdout);
/* 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.
*/
} else 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");
/* Bill Allombert: revert to C locale */
#ifdef HAVE_LOCALE_H
setlocale(LC_CTYPE, "C");
#endif
}
/*
* 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 raw)
{
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(raw);
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(raw);
} 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, " -raw Display non-printable characters in comments (unsafe)\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, raw = 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 if (keymatch(arg, "raw", 1)) {
raw = 1;
} 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, raw);
/* All done. */
exit(EXIT_SUCCESS);
return 0; /* suppress no-return-value warnings */
}