This is a ruby wrapper for the perceptual image diff utility (http://pdiff.sourceforge.net/).
I accidentally stumbled upon this interesting library a year ago, so I decided to write 
a ruby wrapper for it.  The program will take in two images and compared them using the 
perceptual image diff utility.  The output is also another image, and it will highlight the 
differences between the input images.

I actually wrote this over a year ago.  As far as I know, the program should run, but I haven't
check it recently.


Below is the reasoning for perceptual diff utility copied from http://pdiff.sourceforge.net/

Why? I can look at the images myself

So why would I use a program to tell me if two images are similar if I can tell the difference myself by eyeballing it?
Well the utility of this program really shines in the context of QA of rendering algorithms.
During regression testing of a renderer, hundreds of images are generated from an older version of the renderer and are compared
with a newer version of the renderer. This program drastically reduces the number of false positives (failures that are not actually failures)
caused by differences in random number generation, OS or machine architecture differences. Also, you do not
want a human looking at hundreds of images when you can get the computer to do it for you nightly on a cron job.