iOS: how to reduce size of large PNG files

Question

I\'m currently optimizing my iOS app for the new iPad. Unfortunately by adding launch images for the iPad retina display the size of my ipa grows from 1.2MB to

Answer 1

I was able to get it down to 633KB with pngquant (64 colors with slight dithering, which is barely noticeable on regular screen, and should be absolutely invisible at Retina resolution) and ImageOptim.

Yes, you will need to disable Xcode's conversion to avoid Xcode inflating files by converting them to ARGB.

NB: the article quoted in the accepted answer provides no benchmarks at all for the claimed speed difference.
It also contains correction that it is possible to optimize images with ImageOptim for iOS apps.