[Cyykratahk]

Great article

Earlier this year I created my own ICO editor for fun [1]. I learned a lot about reading and writing binary files, and decoding BMP data. While testing the editor on existing site favicons I kept finding that they were all uncompressed BMP data, and came to a similar conclusion to your article after checking the icons used on the Alexa top 100 sites.

I guess this is a combination of the ICO format being somewhat opaque (it's hard to tell if it's using BMP or PNG without using a hex editor), and that there aren't many applications available that create PNG-based ICO files in the first place (especially ones that are used in web development pipelines).

1. https://ico-editor.lach.app/ - Client-side ICO viewer/editor, can open and convert BMP to PNG.

PS. I noticed that your own site's favicon is uncompressed.

[account42]

PNG support in .ico files was introduced in Windows Vista and I expect Internet Explorer just supports whatever the OS does. There might still be holdovers (both sites and tools) from when people cared about XP support.