I'm sorry, I forgot to show how to write out the image, silly me!

$img->write(
  { 
   file  => $tmp->filename, 
   type  => 'tiff', 
   class => 'fax',
   }
);
[download]

And then in order to get the Group4 compression I did resort to ImageMagick's convert util.

   system("convert -page Letter -compress Group4 $filename $filename")
+;
[download]

The last part I'm still not completely happy with, but since this is a batch process I didn't have to worry so much about having the extra system call.