# getjsize.pl
#
# (p) Jerry Nagasaki
# Last update: 2007/11/10

# Extracts JPG/JPEG picture size in pixels from input file


# get file name
$filename = $ARGV[0] || "";

$jpglen = -s $filename;		# get file size
open(FILE, "<./$filename") || die "File not found\n";
binmode(FILE);			# kill possible M$-DOS 0x0D 0x0A sequence for "\n"
$readbytes = read(FILE, $jpgfile, $jpglen);
close(FILE);

# convert file string into "indexed binary" array for easy access via $jpg[$address]
@jpg = split(//, $jpgfile);	# convert each byte into array-element
@jpg = map(ord, @jpg);		# convert each elements to binary value

$width  = 0;
$height = 0;
$i      = 0;

# scan the file for "Baseline DCT" (0xFF, 0xC0)
while ($i < ($jpglen - 9))
{		
	if (($jpg[$i] == 0xFF) && ($jpg[$i + 1] == 0xC0))
	{
		# Baseline DCT coding:
		#
		# +0 +1 +2 +3 +4 +5 +6 +7 +8
		# FF C0 xx xx xx HH HL WH WL  (XH = High Byte, XL = Low Byte, HX = Height, WX = Width)

		$height = $jpg[$i + 5] * 256 + $jpg[$i + 6];
		$width  = $jpg[$i + 7] * 256 + $jpg[$i + 8];
		last;		# "Baseline DCT" found and end while-loop immediately
	}	
	$i++;
}

if ($width && $height)		# both unequal to 0?
{
	print "Picture Height: $height\n";
	print "Picture Width:  $width\n";
}
else
{
	print "ERROR: No Baseline DCT found\n";
}