[bz2]

Kornel is also behind the DSSIM library (in Rust), which I've found useful for comparing images before and after compression.

https://github.com/kornelski/dssim

[pornel]

Fun fact: I wrote DSSIM as a development tool specifically for pngquant, because I needed a way to measure improvements in dithering. Classic per-pixel algorithms only saw it as added noise.

[Y-bar]

And the excellent Mac OS image compression utility ImageOptim: https://imageoptim.com/mac