Apple Icon Image format
The Apple Icon Image format is the icon format used in Apple Inc.'s Mac OS X. It supports icons of 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.
File structure
The file format consists of an 8 byte header, followed by any number of icons.
Header
| Offset |
Size |
Purpose |
| 0 |
4 |
Magic literal, must be "icns" (0x69, 0x63, 0x6e, 0x73) |
| 4 |
4 |
Length of file, in bytes, msb first |
Icon data
| Offset |
Size |
Purpose |
| 0 |
4 |
Icon type, see OSType below. |
| 4 |
4 |
Length of data, in bytes (including type and length), msb first |
| 8 |
Variable |
Icon data |
Compression
Over time the format has been improved and there is support for compression of some parts of the pixel data. The 32-bit ("is32", "il32", "ih32","it32") pixel data is often compressed (per channel) with a format similar to PackBits.[1]
Some sources mentioned that the OS supports both compressed or uncompressed data chunks.
Icon types
| OSType |
Length (bytes) |
Size (pixels) |
Supported OS Version |
Description |
| ICON |
128 |
32 |
1.0 |
32×32 1-bit mono icon |
| ICN# |
256 |
32 |
6.0 |
32×32 1-bit mono icon with 1-bit mask |
| icm# |
48 |
16 |
6.0 |
16×12 1 bit mono icon with 1-bit mask |
| icm4 |
96 |
16 |
7.0 |
16×12 4 bit icon |
| icm8 |
192 |
16 |
7.0 |
16×12 8 bit icon |
| ics# |
64 (32 img + 32 mask) |
16 |
6.0 |
16×16 1-bit mask |
| ics4 |
128 |
16 |
7.0 |
16×16 4-bit icon |
| ics8 |
256 |
16 |
7.0 |
16x16 8 bit icon |
| is32 |
varies (768) |
16 |
8.5 |
16×16 24-bit icon |
| s8mk |
256 |
16 |
8.5 |
16x16 8-bit mask |
| icl4 |
512 |
32 |
7.0 |
32×32 4-bit icon |
| icl8 |
1,024 |
32 |
7.0 |
32×32 8-bit icon |
| il32 |
varies (3,072) |
32 |
8.5 |
32x32 24-bit icon |
| l8mk |
1,024 |
32 |
8.5 |
32×32 8-bit mask |
| ich# |
288 |
48 |
8.5 |
48×48 1-bit mask |
| ich4 |
1,152 |
48 |
8.5 |
48×48 4-bit icon |
| ich8 |
2,304 |
48 |
8.5 |
48×48 8-bit icon |
| ih32 |
varies (6,912) |
48 |
8.5 |
48×48 24-bit icon |
| h8mk |
2,304 |
48 |
8.5 |
48×48 8-bit mask |
| it32 |
varies (49,152) |
128 |
10.0 |
128×128 24-bit icon |
| t8mk |
16,384 |
128 |
10.0 |
128×128 8-bit mask |
| icp4 |
varies |
16 |
10.7 |
16x16 icon in JPEG 2000 or PNG format |
| icp5 |
varies |
32 |
10.7 |
32x32 icon in JPEG 2000 or PNG format |
| icp6 |
varies |
64 |
10.7 |
64x64 icon in JPEG 2000 or PNG format |
| ic07 |
varies |
128 |
10.7 |
128x128 icon in JPEG 2000 or PNG format |
| ic08 |
varies |
256 |
10.5 |
256×256 icon in JPEG 2000 or PNG format |
| ic09 |
varies |
512 |
10.5 |
512×512 icon in JPEG 2000 or PNG format |
| ic10 |
varies |
1024 |
10.7 |
1024×1024 in 10.7 (or 512x512@2x "retina" in 10.8) icon in JPEG 2000 or PNG format |
| ic11 |
varies |
32 |
10.8 |
16x16@2x "retina" icon in JPEG 2000 or PNG format |
| ic12 |
varies |
64 |
10.8 |
32x32@2x "retina" icon in JPEG 2000 or PNG format |
| ic13 |
varies |
256 |
10.8 |
128x128@2x "retina" icon in JPEG 2000 or PNG format |
| ic14 |
varies |
512 |
10.8 |
256x256@2x "retina" icon in JPEG 2000 or PNG format |
- the values inside the brackets () in the length column is the uncompressed length.
Other types
| OSType |
Length (bytes) |
Description |
| 'TOC ' |
varies |
"Table of Contents" a list of all image types in the file, and their sizes (added in Mac OS X 10.7) |
| 'icnV' |
4 |
4-byte big endian float - equal to the bundle version number of Icon Composer.app that created to icon |
See also
References
- ↑ Macintosh Icons
External links
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