As of OSX specifications, the pixel standard that can be used are 16 × 16, 32 × 32, 48 × 48, 128 × 128, 256 × 256, 512 × 512, and 1024 × 1024 pixels, with both 1- and 8-bit alpha channels and multiple image states (example: open and closed folders). The fixed-size icons can be scaled by the operating system and displayed at any intermediate size. So how to get the high quality icon from an application on Mac?
You can find the source of info here
You can find the source of info here