PNG compression

[CompressMaster]

Hello users,

I am looking for the BEST possible PNG compressor. I know that PNGs are already compressed and therefore´incompressible´, but it´s possible to fully decompress it and then apply better compressor for raw output - for example PRECOMP. I haven´t tested it, so I cannot say if it´s possible to shrink it losslessly further - I have a 5MB PNG file captured with LENOVO A-2010 smartphone with OpenCamera app. The "identical" (I needed to switch between apps between shots, so the scene may not be 100% identical) scene shooted without it takes approx. 980 KB, but JPEGs cannot be compressed below 50% - btw, I am working on my custom data compressor - BestComp - that will be able to compress ANY kind of data at least to 90% losslessly.

Therefore I need to know if it´s possible to compress PNGs at least to 95% of original size losslessly of course.

Thanks.
CompressMaster

[Shelwien]

PNGs are compressed with deflate, so all deflate recompression tools apply,
and some compression is always possible due to huffman coding redundancy.

In particular, you can try precomp, since it has explicit support for png parsing.
Also maybe paq8px,paq8pxd.

There're also optimization tools with various levels of loss, like pngout,
which optimizes deflate coding, but keeps picture the same.
Its possible to improve compression further by optimizing alpha plane, etc.

Another good approach is to convert png to uncompressed bmp and compress that with relevant tools.
That is, FLIF, BMF -S or paq8px.
If original png generation method is known (eg. libpng), it could be possible to reconstruct it losslessly
with best compression in this case.