Chromium's .icns files

Sizes

.icns files contain multiple sizes of icons. The standard .icns files for Chromium contain icons of the following sizes:

Size	Type
16×16	'is32'/'s8mk'
32×32	'il32'/'l8mk'
128×128	'it32'/'t8mk'
256×256	'ic08' (PNG)
512×512	'ic09' (PNG)

Rationale

The rationale behind these choices is to avoid bugs in icon display. As noted in a bug, having @2x versions of the smaller icons causes blockiness on retina Macs, and in fact, sometimes just having @2x versions of icons would cause them to be preferred even when it doesn't make sense.

At least through macOS 10.11, using the modern ('icp4'–'icp6') types causes scrambling of the icons in display. If the old types work, why mess with them?

Source PNG files

Use whatever tools you want to create the PNG files, but please note that the dimensions of the images in the PNG files must match exactly the size indicated by their filename. This will be enforced by the makeicns2 tool below.

Construction

The tools for .icns construction can be found in src/tools/mac/icons. Compile makeicns2 before you begin by following the directions in its header comment.

In addition, you will need optipng and advpng, which can be found in the optipng and advancecomp packages, respectively, in your favorite port manager.

To construct an .icns file:

1. Assemble a directory (.iconset) containing the five required sizes of icon, in PNG format: 16×16, 32×32, 128×128, 256×256, and 512×512, named 16.png, 32.png, 128.png, 256.png, and 512.png, respectively.
2. Process the .png files with:
   1. optipng -o7 -zm1-9
   2. advpng -z4 -i50
   3. png_fix.py
3. Create the .icns file with the makeicns2 you compiled: makeicns2 <name>.iconset

Deconstruction and other tools

In the src/tools/mac/icons/additional_tools directory there are several other tools that you may find useful in your quest to craft the perfect icons. They are:

• makeicns: This tool takes an .iconset directory of .png files and creates an .icns file containing them. However, it cannot create the old-style data/mask image pairs, which is why makeicns2 is preferred.
• unmakeicns: This tool takes an .icns file and unpacks it into its constituent images. For the old-style data/mask image pairs, this tool will reconstitute the two into a more useful .png file.
• unpackicon: This tool is used by the unmakeicns tool. It takes the data from an old-style data/mask image pair, which is encoded with a simple PackBits-esque RLE scheme, and outputs the data uncompressed. It is available separately should this be a capability you require.
• makepng: This tool is used by the unmakeicns tool. It reconstructs a .png file from the uncompressed data of an old-style data/mask image pair. It is available separately should this be a capability you require.
• maketoc.py: This tool can be used to both create a TOC section for an .icns file, as well as verify one. The makeicns2 tool automatically creates a TOC section, but this tool's verification of these sections may be useful.

To compile these tools, run make in their containing directory. Note that libpng is required.