Files that contain the .icns file extension usually store icon image files. These icon image files are used by the Mac OS X operating system. This file format supports both 1 and 8 bit alpha channels as well as multiple image stages including folder icons in both the opened and closed states.
Each ICNS file is associated with a corresponding application. The ICNS file acts like a container file and stores the individual icon and resources within the file container. The icons contained within the files can be scaled by the user's operating system to adjust to the proper display size.
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If you have additional information about the ICNS file format or software that uses files with the ICNS suffix, please do get in touch - we would love hearing from you.