What's the most optimal PNG internal format for iOS display can be generated from non-Apple platform?

PNG is recommended, fastest format for iOS开发者_运维知识库. However PNG itself have several internal sub-formats. Alpha channel, byte ordering, color depth and etc.

I read Converting a normal PNG to iPhone Optimized format but the Q/A is about to images in bundles. Now I'm generating many thumbnails optimized for iOS from server. I can't use Apple's framework on server. However sub-optimal format is enough too. I want to hear opinions.

Given that Xcode-optimized PNGs are overrated simply creating smallest possible file may be a better option, and pngquant + PNGOUT or AdvPNG are good tools for that.

The iOS SDK runs pngcrush on the images it puts in the application bundle. Looking at the settings it uses would be a good place to start.

$ /Applications/Xcode.app/Contents/Developer\
/Platforms/iPhoneOS.platform/Developer/usr/bin/pngcrush \
-revert-iphone-optimizations -q Local.png Local-standard.png

see http://developer.apple.com/library/ios/#qa/qa1681/_index.html