2 ms·
Well, isn't that what PNG filters do? So in that sense one could build an algorithm on top of LZ77 that tries to reversibly transform data into repeating sequen
by vanderZwan 5y ago
Well, isn't that what PNG filters do? So in that sense one could build an algorithm on top of LZ77 that tries to reversibly transform data into repeating sequences.
- vidarh 5y agoLZ77 is basically the "scaffolding" for every compression method that uses symmetric compressor and decompressors to replicate state so you don't need to transmit it. So the moment you add a function on top that does more complex prediction than copying from the existing stream, you have a general framework that is far more powerful than basic LZ77. NNCP is such an algorithm on top of that general idea.
- pornel 5y agoFilters 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.