[mistercow]

Yeah, technically that's lossy compression, but what I meant was lossy 32-bit PNG; that is, a preprocessing step before the prediction step which makes the result more compressible by the final DEFLATE step while having a minimal impact on quality.

[nitrogen]

That sounds very interesting. I wonder what kinds of transforms would improve compressibility by DEFLATE. I know a bit about PNG's predictors, but not enough about DEFLATE to confidently guess. If you ever work on this, please let me know. I'd like to collaborate.