Xcode comes bundled with pngcrush, you can find it here:

/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/pngcrush

Add it to your path in your .bash_profile or .zshrc to avoid typing in the long nested directories.

export PATH="$PATH:/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/"

If you don’t have Xcode then install using homebrew

brew install pngcrush

usage

pngcrush [options] infile.png outfile.png

options

Options are optional, some interesting ones to note are:

• -iphone (optimize for iPhone OS)
• -revert-iphone-optimizations (convert iPhone OS optimized PNG to a PNG readable on other platforms)