Yeah, I am curious how much you can improve compression by keeping everything 24 bit, but slightly tweaking the color values to make the result more compressibl

Yeah, I am curious how much you can improve compression by keeping everything 24 bit, but slightly tweaking the color values to make the result more compressible. (PNG applies one of five predictors to each line, takes the difference from the prediction, and deflates the result.) For example, as a greedy algorithm: find the best predictor for a line, then tweak the line to reduce the alphabet (round off the difference from predicted values) or to get longer deflate matches (substitute values if they're close and match a previous run).