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