This is a generator for the Apple Icon Image Format (.icns) which reads PNGs without changing them.

It's run like this: createicons x.iconset and outputs a file x.icns.

The input is a .iconset directory with files conforming to the naming scheme for .iconset directories. It reads a 'complete' set of PNG icons as described here: https://developer.apple.com/library/content/documentation/GraphicsAnimation/Conceptual/HighResolutionOSX/Optimizing/Optimizing.html Not all icons in the list have to be present, but only icons with names from the list are processed by createicns.

To generate a .iconset directory from an existing x.icns file, use readicns x.icns

createicns is similar to running iconutil -c icns x.iconset, except it doesn't change the PNG images in any way.

createicns and readicns have only been tested on macOS. Use make createicns and make readicns to compile them.

Say you have a 'complete' set of PNG icons, to make sure your icons look beautiful in all environments, on retina and non-retina. But the PNG files are much bigger than you'd like them to be, and your set is taking up more than 500KB. Luckily their are various (lossy) ways to optimize PNG files, including dithering to reduce the color space. Unfortunately the Apple tool iconutil will happily convert your optimized PNGs back to 32-bit when you run it.

Here's an example of optimizing an iconset using pngquant, which you can find at https://pngquant.org (lines starting with '$' are commands to enter):

• Our existing icon set is stored in icons.icns. Let's extract it.
  • $ readicns icons.icns
  • You should now have a folder icons.iconset whose contents look like this:

$ ls -l icons.iconset
total 1224
-rw-r--r--  1 user01  staff   15903 Jan 17 09:21 icon_128x128.png
-rw-r--r--  1 user01  staff   41182 Jan 17 09:21 [email protected]
-rw-r--r--  1 user01  staff    2462 Jan 17 09:21 [email protected]
-rw-r--r--  1 user01  staff   41182 Jan 17 09:21 icon_256x256.png
-rw-r--r--  1 user01  staff   99938 Jan 17 09:21 [email protected]
-rw-r--r--  1 user01  staff    6070 Jan 17 09:21 [email protected]
-rw-r--r--  1 user01  staff   99938 Jan 17 09:21 icon_512x512.png
-rw-r--r--  1 user01  staff  292329 Jan 17 09:21 [email protected]
-rw-r--r--  1 user01  staff    1826 Jan 17 14:11 icon_data_il32
-rw-r--r--  1 user01  staff     579 Jan 17 14:11 icon_data_is32
-rw-r--r--  1 user01  staff    1024 Jan 17 14:11 icon_data_l8mk
-rw-r--r--  1 user01  staff     256 Jan 17 14:11 icon_data_s8mk

• Optimize the PNGs using pngquant
  • $ cd icons.iconset
  • $ pngquant --ext .png --force *
  • The contents of the folder should now have smaller files:

$ ls -l icons.iconset
total 408
-rw-r--r--  1 user01  staff   6355 Jan 17 09:25 icon_128x128.png
-rw-r--r--  1 user01  staff  13901 Jan 17 09:25 [email protected]
-rw-r--r--  1 user01  staff   1782 Jan 17 09:25 [email protected]
-rw-r--r--  1 user01  staff  13901 Jan 17 09:25 icon_256x256.png
-rw-r--r--  1 user01  staff  31002 Jan 17 09:25 [email protected]
-rw-r--r--  1 user01  staff   3030 Jan 17 09:25 [email protected]
-rw-r--r--  1 user01  staff  31002 Jan 17 09:25 icon_512x512.png
-rw-r--r--  1 user01  staff  82188 Jan 17 09:25 [email protected]
-rw-r--r--  1 user01  staff   1826 Jan 17 14:11 icon_data_il32
-rw-r--r--  1 user01  staff    579 Jan 17 14:11 icon_data_is32
-rw-r--r--  1 user01  staff   1024 Jan 17 14:11 icon_data_l8mk
-rw-r--r--  1 user01  staff    256 Jan 17 14:11 icon_data_s8mk

• Run createicns to get them back into icons.icns
  • $ createicns icons.iconset
  • Open icons.icns using Preview.app to make sure the icons are there and look OK.