+
+# Given the raw body of a GIF document, returns the dimensions of the image.
+#
+sub gif_size($) {
+ my ($body) = @_;
+ my $type = substr($body, 0, 6);
+ my $s;
+ return () unless ($type =~ /GIF8[7,9]a/);
+ $s = substr ($body, 6, 10);
+ my ($a,$b,$c,$d) = unpack ("C"x4, $s);
+ return (($b<<8|$a), ($d<<8|$c));
+}
+
+# Given the raw body of a JPEG document, returns the dimensions of the image.
+#
+sub jpeg_size($) {
+ my ($body) = @_;
+ my $i = 0;
+ my $L = length($body);
+
+ my $c1 = substr($body, $i, 1); $i++;
+ my $c2 = substr($body, $i, 1); $i++;
+ return () unless (ord($c1) == 0xFF && ord($c2) == 0xD8);
+
+ my $ch = "0";
+ while (ord($ch) != 0xDA && $i < $L) {
+ # Find next marker, beginning with 0xFF.
+ while (ord($ch) != 0xFF) {
+ return () if (length($body) <= $i);
+ $ch = substr($body, $i, 1); $i++;
+ }
+ # markers can be padded with any number of 0xFF.
+ while (ord($ch) == 0xFF) {
+ return () if (length($body) <= $i);
+ $ch = substr($body, $i, 1); $i++;
+ }
+
+ # $ch contains the value of the marker.
+ my $marker = ord($ch);
+
+ if (($marker >= 0xC0) &&
+ ($marker <= 0xCF) &&
+ ($marker != 0xC4) &&
+ ($marker != 0xCC)) { # it's a SOFn marker
+ $i += 3;
+ return () if (length($body) <= $i);
+ my $s = substr($body, $i, 4); $i += 4;
+ my ($a,$b,$c,$d) = unpack("C"x4, $s);
+ return (($c<<8|$d), ($a<<8|$b));
+
+ } else {
+ # We must skip variables, since FFs in variable names aren't
+ # valid JPEG markers.
+ return () if (length($body) <= $i);
+ my $s = substr($body, $i, 2); $i += 2;
+ my ($c1, $c2) = unpack ("C"x2, $s);
+ my $length = ($c1 << 8) | $c2;
+ return () if ($length < 2);
+ $i += $length-2;
+ }
+ }
+ return ();
+}
+
+# Given the raw body of a PNG document, returns the dimensions of the image.
+#
+sub png_size($) {
+ my ($body) = @_;
+ return () unless ($body =~ m/^\211PNG\r/s);
+ my ($bits) = ($body =~ m/^.{12}(.{12})/s);
+ return () unless defined ($bits);
+ return () unless ($bits =~ /^IHDR/);
+ my ($ign, $w, $h) = unpack("a4N2", $bits);
+ return ($w, $h);
+}
+
+
+# Given the raw body of a GIF, JPEG, or PNG document, returns the dimensions
+# of the image.
+#
+sub image_size($) {
+ my ($body) = @_;
+ return () if (length($body) < 10);
+ my ($w, $h) = gif_size ($body);
+ if ($w && $h) { return ($w, $h); }
+ ($w, $h) = jpeg_size ($body);
+ if ($w && $h) { return ($w, $h); }
+ # #### TODO: need image parsers for TIFF, XPM, XBM.
+ return png_size ($body);
+}
+
+# Returns the dimensions of the image file.
+#
+sub image_file_size($) {
+ my ($file) = @_;
+ my $in;
+ if (! open ($in, '<', $file)) {
+ print STDERR "$progname: $file: $!\n" if ($verbose);
+ return undef;
+ }
+ binmode ($in); # Larry can take Unicode and shove it up his ass sideways.
+ my $body = '';
+ sysread ($in, $body, 1024 * 50); # The first 50k should be enough.
+ close $in; # (It's not for certain huge jpegs...
+ return image_size ($body); # but we know they're huge!)
+}
+
+
+sub error($) {
+ my ($err) = @_;
+ print STDERR "$progname: $err\n";
+ exit 1;
+}
+
+sub usage() {
+ print STDERR "usage: $progname [--verbose] directory\n" .
+ " Prints the name of a randomly-selected image file. The directory\n" .
+ " is searched recursively. Images smaller than " .
+ "${min_image_width}x${min_image_height} are excluded.\n";