Filters in PNG are not too bad for what could be done with an off-the-shelf gzip and a few lines of code, but as a compression mechanism they work poorly. All

Filters in PNG are not too bad for what could be done with an off-the-shelf gzip and a few lines of code, but as a compression mechanism they work poorly. All compression is prediction + entropy coding. The entropy coding part is a solved problem. Inserting LZ77 between your predictor and the entropy coder just makes it harder to communicate the exact symbols and probabilities you have predicted. If you're building a rocket: you can strap a rocket engine to a car, and it will still go faster than the car itself, but it's easier not to build it on top of a car.