Tip: revert pngcrush optimization in Xcode 4.3
When you are adding PNG images to an iOS app, Xcode will optimize and compress them when compiling, using a tool called pngcrush. To revert this optimization back, copy the .png files from the .ipa bundle into some folder and run this in terminal
/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/pngcrush -dir SOME_DIR -revert-iphone-optimizations -q *.png
SOME_DIR is a destination path, something like ~/temp.