Challenge: Speed up seam carving example

Hi all, I have placed an example of seam carving here: https://github.com/stefanv/scikits.image-1/blob/seam_carving/doc/examples/pl... The idea is super simple, but currently it's too slow. I'm curious to see if anyone can improve its execution time? If you haven't seen seam carving before, take a look at the video link in the docstring. Regards Stéfan