The following pseudocode decompresses the data: However, manually crafting icns files with uncompressed 24-bit RGB or ARGB images will not display properly – at least on newer macOS releases (tested on macOS 11). Some sources mention that the OS supports both compressed or uncompressed data chunks. The 24-bit RGB ( is32, il32, ih32, it32, icp4, icp5) and ARGB ( ic04, ic05, icsb) pixel data are compressed (per channel) with a format similar to PackBits. Over time the format has been improved and there is support for compression of some parts of the pixel data. So, if you want to save the data to a file you have to prepend the icns header. The data for all nested icns files does not contain the icns file-header.The table of contents is a list of all contained types (4 byte type-name + 4 byte length).Allows automatic icon switching in Dark mode. Usage unknown (only name field seems to be used). Usage unknown (all tested files use either "icon" or "template" ).
APPLE FINDER ICON HISTORY MAC OS X
"Table of Contents" a list of all image types in the file, and their sizes (added in Mac OS X 10.7)Ĥ-byte big endian float - equal to the bundle version number of Icon Composer.app that created the icon Therefore, the supported OS version may not be accurate or adjusted based on file format. The support for newer image types seems to be introduced later than the key field (see previous two points).The 24-bit RGB icons ( is32, il32, ih32, it32) also allow images in JPEG 2000 and PNG format (tested on macOS 10.15.7 and macOS 11).Yet, even the ARGB keys can be displayed on macOS 10.15 if you set a JPEG 2000 or PNG image (see footnote on usage in app packages above). ARGB images are only supported in macOS 11 and newer – macOS 10.15.7 does not display ARGB images.the ARGB fields also accept files in PNG format – but not vice versa, you can not put ARGB images in any of the PNG-only fields (tested on macOS 11).The ARGB format consists of the ascii values for 'ARGB' and the four compressed channels tightly packed (see Compression).The it32 icon must start with a four-byte header, see footnote above. The 24-bit RGB format consists of the three compressed channels tightly packed (see Compression).The 4-bit an 8-bit icons use a fixed color palette with 128 colors and 256 colors respectively.Mono icons with alpha mask can display three colors: white, black, and transparent.
These formats are supported in standalone icns files but do not display properly if used as application icon inside a.
Usage unknown, the four zero-bytes can be any value and are quietly ignored. it32 data always starts with a header of four zero-bytes (tested all icns files in macOS 10.15.7 and macOS 11). The value inside the parenthesis is the uncompressed length for ARGB and 24-bit RGB icons. JPEG 2000 or PNG format "retina" in 10.8)ĪRGB or JPEG 2000 † or PNG † format "retina") JPEG 2000 † or PNG † format or 24-bit RGB icon Length of data, in bytes (including type and length), msb first The file format consists of an 8 byte header, followed by any number of icons.
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