Apple Icon Image format

Apple Icon Image
Filename extension	.icns
Internet media type	image/x-icns
Type code	icns
Uniform Type Identifier (UTI)	com.apple.icns
Magic number	69 63 6e 73
Developed by	Apple Inc.
Type of format	Icon file format

The Apple Icon Image format (.icns) is an icon format used in Apple Inc.'s macOS. It supports icons of 16 × 16, 32 × 32, 48 × 48, 128 × 128, 256 × 256, 512 × 512 points at 1x and 2x scale, 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.

As of macOS 11, asset catalogs are the preferred file format for macOS custom icons.^[1]