macOS ICNS icon format #453
Description
Issue #170 was originally for ICNS, ICO, and EXE thumbnailing. I decided to split ICNS into another issue because it's both more and less complicated than ICO.
- More complicated: Prior to Mac OS X 10.7, ICO doesn't have a directory.
- Less complicated: Instead of planes, bitcounts, color counts, etc., there's a fixed set of fourCCs, which I assume map directly to Macintosh Classic resource types (or subtypes). Also, the palette for 4-bit and 8-bit icons is fixed; that is, it's part of the OS, not the icon.
Reference: https://en.wikipedia.org/wiki/Apple_Icon_Image_format