This article has some... interesting entries (as noted elsewhere in the comments here), but it came up at an interesting moment for me. I spent last weekend poring over the PNG spec because I wanted to make QR codes real small [1]. I'm completely obsessed now. I'm going to dig into some other formats...

[1]: https://github.com/qubyte/qrcode-png/blob/main/index.js#L6-L...