The original repository is from: https://github.com/swcai/iphone-png-normalizer.
The PNG file format inside iPhone application is slightly different from normal PNG files. So when you get the png images from iphone app package, you should make some conversion.
I wrote this handy Ruby script to do it for me. Let me know if you think it is useful.
I found it super useful! I added a slight layer to make it useful (as a replacement for pngcrush w/ minimal options) on a linux system. Huzzah for Open Source!