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Taken from http://jpegclub.org//jpegexiforient.c on 13 Jan 2014
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@CiderMan
CiderMan committed Jan 14, 2014
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300 changes: 300 additions & 0 deletions jpegexiforient.c
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/*
* jpegexiforient.c
*
* This is a utility program to get and set the Exif Orientation Tag.
* It can be used together with jpegtran in scripts for automatic
* orientation correction of digital camera pictures.
*
* The Exif orientation value gives the orientation of the camera
* relative to the scene when the image was captured. The relation
* of the '0th row' and '0th column' to visual position is shown as
* below.
*
* Value | 0th Row | 0th Column
* ------+-------------+-----------
* 1 | top | left side
* 2 | top | right side
* 3 | bottom | right side
* 4 | bottom | left side
* 5 | left side | top
* 6 | right side | top
* 7 | right side | bottom
* 8 | left side | bottom
*
* For convenience, here is what the letter F would look like if it were
* tagged correctly and displayed by a program that ignores the orientation
* tag:
*
* 1 2 3 4 5 6 7 8
*
* 888888 888888 88 88 8888888888 88 88 8888888888
* 88 88 88 88 88 88 88 88 88 88 88 88
* 8888 8888 8888 8888 88 8888888888 8888888888 88
* 88 88 88 88
* 88 88 888888 888888
*
*/

#include <stdio.h>
#include <stdlib.h>

static FILE * myfile; /* My JPEG file */

static unsigned char exif_data[65536L];

/* Return next input byte, or EOF if no more */
#define NEXTBYTE() getc(myfile)

/* Error exit handler */
#define ERREXIT(msg) (exit(0))

/* 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);
}

static const char * progname; /* program name for error messages */

static void
usage (FILE *out)
/* complain about bad command line */
{
fprintf(out, "jpegexiforient reads or writes the Exif Orientation Tag ");
fprintf(out, "in a JPEG Exif file.\n");

fprintf(out, "Usage: %s [switches] jpegfile\n", progname);

fprintf(out, "Switches:\n");
fprintf(out, " --help display this help and exit\n");
fprintf(out, " --version output version information and exit\n");
fprintf(out, " -n Do not output the trailing newline\n");
fprintf(out, " -1 .. -8 Set orientation value 1 .. 8\n");
}

/*
* The main program.
*/

int
main (int argc, char **argv)
{
int n_flag, set_flag;
unsigned int length, i;
int is_motorola; /* Flag for byte order */
unsigned int offset, number_of_tags, tagnum;

progname = argv[0];
if (progname == NULL || progname[0] == 0)
progname = "jpegexiforient"; /* in case C library doesn't provide it */

if (argc < 2) { usage(stderr); return 1; }

n_flag = 0; set_flag = 0;

i = 1;
while (argv[i][0] == '-') {
switch (argv[i][1]) {
case '-':
switch (argv[i][2]) {
case 'h': usage(stdout); return 0;
case 'v': fprintf(stdout,"jpegexiforient\n"); return 0;
default: usage(stderr); return 1;
}
case 'n':
n_flag = 1;
break;
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
set_flag = argv[i][1] - '0';
break;
default:
usage(stderr); return 1;
}
if (++i >= argc) { usage(stderr); return 1; }
}

if (set_flag) {
if ((myfile = fopen(argv[i], "rb+")) == NULL) {
fprintf(stderr, "%s: can't open %s\n", progname, argv[i]);
return 0;
}
} else {
if ((myfile = fopen(argv[i], "rb")) == NULL) {
fprintf(stderr, "%s: can't open %s\n", progname, argv[i]);
return 0;
}
}

/* Read File head, check for JPEG SOI + Exif APP1 */
for (i = 0; i < 4; i++)
exif_data[i] = (unsigned char) read_1_byte();
if (exif_data[0] != 0xFF ||
exif_data[1] != 0xD8 ||
exif_data[2] != 0xFF ||
exif_data[3] != 0xE1)
return 0;

/* Get the marker parameter length count */
length = read_2_bytes();
/* Length includes itself, so must be at least 2 */
/* Following Exif data length must be at least 6 */
if (length < 8)
return 0;
length -= 8;
/* Read Exif head, check for "Exif" */
for (i = 0; i < 6; i++)
exif_data[i] = (unsigned char) read_1_byte();
if (exif_data[0] != 0x45 ||
exif_data[1] != 0x78 ||
exif_data[2] != 0x69 ||
exif_data[3] != 0x66 ||
exif_data[4] != 0 ||
exif_data[5] != 0)
return 0;
/* Read Exif body */
for (i = 0; i < length; i++)
exif_data[i] = (unsigned char) read_1_byte();

if (length < 12) return 0; /* Length of an IFD entry */

/* Discover byte order */
if (exif_data[0] == 0x49 && exif_data[1] == 0x49)
is_motorola = 0;
else if (exif_data[0] == 0x4D && exif_data[1] == 0x4D)
is_motorola = 1;
else
return 0;

/* Check Tag Mark */
if (is_motorola) {
if (exif_data[2] != 0) return 0;
if (exif_data[3] != 0x2A) return 0;
} else {
if (exif_data[3] != 0) return 0;
if (exif_data[2] != 0x2A) return 0;
}

/* Get first IFD offset (offset to IFD0) */
if (is_motorola) {
if (exif_data[4] != 0) return 0;
if (exif_data[5] != 0) return 0;
offset = exif_data[6];
offset <<= 8;
offset += exif_data[7];
} else {
if (exif_data[7] != 0) return 0;
if (exif_data[6] != 0) return 0;
offset = exif_data[5];
offset <<= 8;
offset += exif_data[4];
}
if (offset > length - 2) return 0; /* check end of data segment */

/* Get the number of directory entries contained in this IFD */
if (is_motorola) {
number_of_tags = exif_data[offset];
number_of_tags <<= 8;
number_of_tags += exif_data[offset+1];
} else {
number_of_tags = exif_data[offset+1];
number_of_tags <<= 8;
number_of_tags += exif_data[offset];
}
if (number_of_tags == 0) return 0;
offset += 2;

/* Search for Orientation Tag in IFD0 */
for (;;) {
if (offset > length - 12) return 0; /* check end of data segment */
/* Get Tag number */
if (is_motorola) {
tagnum = exif_data[offset];
tagnum <<= 8;
tagnum += exif_data[offset+1];
} else {
tagnum = exif_data[offset+1];
tagnum <<= 8;
tagnum += exif_data[offset];
}
if (tagnum == 0x0112) break; /* found Orientation Tag */
if (--number_of_tags == 0) return 0;
offset += 12;
}

if (set_flag) {
/* Set the Orientation value */
if (is_motorola) {
exif_data[offset+2] = 0; /* Format = unsigned short (2 octets) */
exif_data[offset+3] = 3;
exif_data[offset+4] = 0; /* Number Of Components = 1 */
exif_data[offset+5] = 0;
exif_data[offset+6] = 0;
exif_data[offset+7] = 1;
exif_data[offset+8] = 0;
exif_data[offset+9] = (unsigned char)set_flag;
exif_data[offset+10] = 0;
exif_data[offset+11] = 0;
} else {
exif_data[offset+2] = 3; /* Format = unsigned short (2 octets) */
exif_data[offset+3] = 0;
exif_data[offset+4] = 1; /* Number Of Components = 1 */
exif_data[offset+5] = 0;
exif_data[offset+6] = 0;
exif_data[offset+7] = 0;
exif_data[offset+8] = (unsigned char)set_flag;
exif_data[offset+9] = 0;
exif_data[offset+10] = 0;
exif_data[offset+11] = 0;
}
fseek(myfile, (4 + 2 + 6 + 2) + offset, SEEK_SET);
fwrite(exif_data + 2 + offset, 1, 10, myfile);
} else {
/* Get the Orientation value */
if (is_motorola) {
if (exif_data[offset+8] != 0) return 0;
set_flag = exif_data[offset+9];
} else {
if (exif_data[offset+9] != 0) return 0;
set_flag = exif_data[offset+8];
}
if (set_flag > 8) return 0;
}

/* Write out Orientation value */
if (n_flag)
printf("%c", '0' + set_flag);
else
printf("%c\n", '0' + set_flag);

/* All done. */
return 0;
}

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