[Matroska-devel] Re: [png-list] Request for a hi-speed bitmap compression format standard

Cosmin Truta cosmin at cs.toronto.edu
Thu Aug 14 21:22:27 CEST 2003


> 1. Is there any chance to make PNG much faster than it currently is,
> even with the disadvantage of a much lower compression ratio than what
> you guys normally achieve, but still be PNG spec compliant ? To be
> more precise, the PNGs created with our 'special' compressor should be
> decodable by any existing PNG decompressor lib, even when being slow.
> Of course, we know we have to use a special modified lib for
> decompressing at the desired high speed in real time, to gain the
> speed advantage, but thats ok with us.

You might want to try a beta version of the upcoming zlib-1.2:

  http://www.alumni.caltech.edu/~madler/zlib-1.2.0.3.tar.gz

It has a faster decompression and a faster CRC. I admit the differences
are not so spectacular. But, as Adam suggested, you could try to remove
the Adler32 and CRC32 checks completely.

Furthermore, if you are using Intel x86, there is an ASM version of
inflate at http://www.charm.net/~christop/zlib/

The new zlib release should appear within a few weeks.


> More tests were done, and the best solution we currently have is to
> use lzo on the original RLE precompressed subtitles, with a 1:7
> compression ratio.

Be careful about this one!

According to comp.compression FAQ, there is a patent (4,988,998) that
covers RLE followed by Ziv-Lempel 77. Ridiculous? Yes, but that still
prevents you from using the method.

  http://www.faqs.org/faqs/compression-faq/part1/section-7.html

On the other hand, you could try RLE followed by LZW, if you can wait
one more year, until the LZW patent expires worldwide.

Best regards,
Cosmin




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