Viewing iPhone-Optimized PNGs

Q: When I build my iPhone OS application, Xcode optimizes the PNG files within my application's bundle, meaning that Preview can't display them. How can I view these optimized files?

A: When I build my iPhone OS application, Xcode optimizes the PNG files within my application's bundle, meaning that Preview can't display them. How can I view these optimized files?

This optimization is done by the pngcrush tool, which you can find in /Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/pngcrush (assuming you installed the iPhone SDK in the standard place). In iPhone SDK 3.2 and later, the pngcrush tool supports a command line option, -revert-iphone-optimizations, that undoes the optimizations done during the Xcode build process. So, to view an optimized PNG file, you should first undo the optimization and then open it with Preview.

Listing 1 shows how you can use the pngcrush tool to convert an iPhone-optimized PNG file (Local.png) to a standard PNG file (Local-standard.png).

Listing 1 Undoing iPhone PNG optimization

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

批量将优化后的PNG文件转换为正常可预览的PNG文件：

/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/pngcrush -revert-iphone-optimizations -d outdir *.png