In addition, the ICNS file supports 1-bit as well as 8-bit alpha channels. This format is pretty handy as a base for the ICNS since it allows transparency.
The content of the ICNS file typically consists of one or more images in the PNG format. However, PNG was designed for transferring images on the Internet, not for professional-quality print graphics, and therefore does not support non-RGB color spaces such as CMYK. PNG supports palette-based images (with palettes of 24-bit RGB or 32-bit RGBA colors), grayscale images (with or without alpha channel), and full-color non-palette-based RGB images (with or without alpha channel). As of OS X Mountain Lion, ICNS files can support even bigger images, namely the 1024x1024 pixels dimension.
They range from 16x16 pixels to 512x512 pixels. ICNS files support images in a variety of dimensions. These icon files display a small image (icon) in the OSX Finder or dock, a representative for an application to which it is linked. Icon files used on Mac computers and other OS X devices use the file extension ICNS. However, PNG itself does not support animation at all. PNG was created as an improved, non-patented replacement for Graphics Interchange Format (GIF) and is the most used lossless image compression format on the Internet. Portable Network Graphics (PNG) is a raster graphics file format that supports lossless data compression.
