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/*
* Copyright (c) 2001, 2002, Eric M. Johnston <emj@postal.net>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by Eric M. Johnston.
* 4. Neither the name of the author nor the names of any co-contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $Id: jpeg.c,v 1.5 2002/10/15 02:57:09 ejohnst Exp $
*/
/*
* This module contains a minimal set of functions for parsing a JPEG
* file, specific for use in extracting EXIF information. Primarily, it
* reads the input file and looks for the markers which indicate the start
* of APP1 and APP2 sections.
*
* Portions of this code were developed while referencing the public domain
* 'Jhead' program (version 1.2) by Matthias Wandel <mwandel@rim.net>.
*/
#include <stdio.h>
#include "jpeg.h"
#include "exif.h"
static FILE *infile;
/* Some data we collect from a start of frame. */
static int jpg_prcsn; /* Precision. */
static int jpg_cmpnts; /* Number of components. */
static unsigned int jpg_height; /* Image height. */
static unsigned int jpg_width; /* Image width. */
static const char *jpg_prcss; /* Process. */
static int seensof;
/* Process string lookup table. */
static struct jpgprocess {
int sof;
const char *str;
} process[] = {
{ JPEG_M_SOF0, "Baseline" },
{ JPEG_M_SOF1, "Extended sequential" },
{ JPEG_M_SOF2, "Progressive" },
{ JPEG_M_SOF3, "Lossless" },
{ JPEG_M_SOF5, "Differential sequential" },
{ JPEG_M_SOF6, "Differential progressive" },
{ JPEG_M_SOF7, "Differential lossless" },
{ JPEG_M_SOF9, "Extended sequential, arithmetic coding" },
{ JPEG_M_SOF10, "Progressive, arithmetic coding" },
{ JPEG_M_SOF11, "Lossless, arithmetic coding" },
{ JPEG_M_SOF13, "Differential sequential, arithmetic coding" },
{ JPEG_M_SOF14, "Differential progressive, arithmetic coding" },
{ JPEG_M_SOF15, "Differential lossless, arithmetic coding" },
{ JPEG_M_ERR, "Unknown" },
};
/*
* Fetch one byte of the JPEG file.
*/
static int
jpg1byte(void)
{
int b;
b = fgetc(infile);
if (b == EOF)
exifdie("invalid JPEG format");
return (b);
}
/*
* Fetch two bytes of the JPEG file.
*/
static unsigned int
jpg2byte(void)
{
unsigned int b1, b2;
b1 = fgetc(infile);
b2 = fgetc(infile);
if (b1 == EOF || b2 == EOF)
exifdie("invalid JPEG format");
return ((b1 << 8) | b2);
}
/*
* Fetch the length of a marker.
*/
static unsigned int
mkrlen(void)
{
unsigned int l;
/* Length includes itself. */
if ((l = jpg2byte()) < 2)
exifdie("invalid JPEG marker (length mismatch)");
return (l - 2);
}
/*
* Skip over an uninteresting marker.
*/
static void
skipmkr(void)
{
unsigned int l;
l = mkrlen();
while (l) {
jpg1byte();
l--;
}
}
/*
* Check the first bytes of the file for a marker.
*/
static int
topmkr(void)
{
if (jpg1byte() != JPEG_M_BEG)
return (JPEG_M_ERR);
return (jpg1byte());
}
/*
* Find the next JPEG marker in the file.
*/
static int
nxtmkr(void)
{
int b;
int bad = 0;
/* Read until we see JPEG_MARKER. */
while ((b = jpg1byte()) != JPEG_M_BEG)
bad++;
/* Read all JPEG_M_BEGs (which may be used for padding). */
while ((b = jpg1byte()) == JPEG_M_BEG);
if (bad)
exifwarn("skipped spurious bytes in JPEG");
return (b);
}
/*
* Collect image data from the start of frame.
* XXX Note that we clobber any previously collected info...
*/
static void
sofmrk(int mark)
{
int i;
unsigned int l;
l = mkrlen();
jpg_prcsn = jpg1byte();
jpg_height = jpg2byte();
jpg_width = jpg2byte();
jpg_cmpnts = jpg1byte();
for (i = 0; process[i].sof < JPEG_M_ERR; i++)
if (process[i].sof == mark)
break;
jpg_prcss = process[i].str;
/* Verify length. */
if (l != (unsigned int)(6 + jpg_cmpnts * 3))
exifdie("invalid JPEG SOF marker (length mismatch)");
/* Skip over component info we don't care about. */
for (i = 0; i < jpg_cmpnts; i++) {
jpg1byte(); jpg1byte(); jpg1byte();
}
seensof = TRUE;
}
/*
* Scan through a JPEG file for markers, returning interesting ones.
* Returns false when it's done with the file.
*/
int
jpegscan(FILE *fp, int *mark, unsigned int *len, int first)
{
infile = fp;
/* First time through. */
if (first && topmkr() != JPEG_M_SOI) {
exifwarn("doesn't appear to be a JPEG file; "
"searching for start of image");
if (nxtmkr() != JPEG_M_SOI)
exifdie("start of image not found");
}
/* Look for interesting markers. */
for (;;) {
switch ((*mark = nxtmkr())) {
case JPEG_M_EOI:
case JPEG_M_SOS:
return (FALSE);
case JPEG_M_APP1:
case JPEG_M_APP2:
*len = mkrlen();
return (TRUE);
/* We might as well collect some useful info from SOFs. */
case JPEG_M_SOF0:
case JPEG_M_SOF1:
case JPEG_M_SOF3:
case JPEG_M_SOF5:
case JPEG_M_SOF6:
case JPEG_M_SOF7:
case JPEG_M_SOF9:
case JPEG_M_SOF10:
case JPEG_M_SOF11:
case JPEG_M_SOF13:
case JPEG_M_SOF14:
case JPEG_M_SOF15:
sofmrk(*mark);
break;
/* Just skip past markers we don't care about. */
default:
skipmkr();
}
}
return (FALSE);
}
/*
* Returns some basic image info about the JPEG, gleaned from start of
* frame sections.
*/
int
jpeginfo(int *prcsn, int *cmpnts, unsigned int *height, unsigned int *width,
const char *prcss)
{
*prcsn = jpg_prcsn;
*cmpnts = jpg_cmpnts;
*height = jpg_height;
*width = jpg_width;
prcss = jpg_prcss;
return (seensof);
}
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