-# Find the background colour. We assume the image already has a
-# border, so this is just the pixel colour of the top left corner.
-$back = $data->[0];
+# Find the background colour, by looking around the entire border
+# and finding the most popular pixel colour.
+for ($i = 0; $i < $w; $i++) {
+ $pcount{$data->[$i]}++; # top row
+ $pcount{$data->[($h-1)*$w+$i]}++; # bottom row
+}
+for ($i = 1; $i < $h-1; $i++) {
+ $pcount{$data->[$i*$w]}++; # left column
+ $pcount{$data->[$i*$w+$w-1]}++; # right column
+}
+@plist = sort { $pcount{$b} <=> $pcount{$a} } keys %pcount;
+$back = $plist[0];