Add another PNG crusher

[jakearchibald]

OptiPNG doesn't seem to do as well as AdvPNG. We should look at porting AdvPNG over.

[jakearchibald]

Candidates:

• https://github.com/google/zopfli (slow but high compression. Not sure if it switches palette modes, so may need to be run through another crusher first).
• https://github.com/shssoichiro/oxipng Multithreaded and Rust version of optipng.
• AdvPNG - Old messy project but seems to be a good trade off in terms of speed and size reduction.
• https://github.com/fhanau/Efficient-Compression-Tool scores well in https://css-ig.net/png-tools-overview, but as far as I can tell, it's just a wrapper around other tools.

[tobdub]

Maybe something like pngquant (https://pngquant.org/) can be interesting for lossy PNG compression. It feels like squoosh is especially good for lossy compression since it makes it easy to compare the before and after pictures.

[jakearchibald]

@tobiasdubois the "reduce palette" preprocessor uses libquant which powers pngquant. We seperated it so you can use it with webp lossless too (you can also use it with jpeg, but there isn't a lot of point).

[tracker1]

Would love to see a quantization option with palette reduction on the output... huge benefits in many cases.

[surma]

@tracker1 Squoosh already offers that. It’s under “Reduce palette”

[RReverser]

Just to add one more compressor that isn't listed above: PNGWolf. Code on Github: https://github.com/hoehrmann/pngwolf.

[surma]

I think we are all quite happy with Oxi :D