The ICNS - Mac OS X Icon Resource file type is commonly used by Mac OS X applications. This particular file type can store one or more images on a Macbook. An ICNS - Mac OS X Icon Resource File can support both one and eight bit alpha channels, display application icons in Mac's OS X Finder and can be created and/or modified using Icon Composer. Those who only want to view the files can do so using Apple's Preview program.
ICNS - Mac OS X Icon Resource Files can support images with various pixels. These files are generally stored in the Contents/Resources/ directory and are used by .PLIST files. While many Mac users do not utilize these files, they are important nonetheless and help the computer function properly.