PNG better than gif....

PNG better than gif....

Post by Micheal Schindle » Sat, 02 Aug 1997 04:00:00




> After taking a couple of people's suggestions to examine PNG, I noticed
> that PNG uses the LZ77 or ZLIB compression. Is there a better lossless
> routine to use on a graphic that has no more than 256 colors?

> Thanks
> Scott Jensen

depends on the image. you may or may not be better off using a blocksort
like in bzip or szip. LZ77 (and most other lossless compressors)
advantage: catches long repetition well, doesnt catch probabilities of
individual symbols well.
blocksort: doesnt catch long repetitions at all, catches local symbol
probabilities better. (longer codes for longer symbol strings versus
short codes for single symbols)

If you have the possibility try szip on your data (sorry, no source code
at the moment), the compression is faster. If you can afford a long
compression time but need fast decompression go for bzip (it may be VERY
slow on compression).
You may want to increase the blocksize in bzip to your imagesize (and
risk a VERY VERY SLOW compression on some files).

you may also want to try other good lossless algorithms, take a look at
A.C.T. http://www.geocities.com/SiliconValley/Park/4264/act.html to see
what is good at the moment. You will also find pointers to the archivers
there.
szip master site: http://eiunix.tuwien.ac.at/~michael/szip/

Michael

http://eiunix.tuwien.ac.at/~michael/

 
 
 

PNG better than gif....

Post by Scott Jense » Sat, 02 Aug 1997 04:00:00


After taking a couple of people's suggestions to examine PNG, I noticed
that PNG uses the LZ77 or ZLIB compression. Is there a better lossless
routine to use on a graphic that has no more than 256 colors?

Thanks
Scott Jensen

 
 
 

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