[Image-SIG] Fast cropping

[cab938 at mail.usask.ca]

I have the need to break a single large image up (3 colour bands) into a series
of smaller images in a grid-like fashion.  The code we have written write now
works, but it's really slow - we essentially walk around the image cropping and
loading to return new PIL Image objects.  Any suggestions on a faster way? 
Should I be using fromBuffer() and pixelaccess to create my sub-images?  I want
Image objects as I use a number of PIL methods after that, I just don't know the
fastest way to create them.

Regards,

Chris