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List:       koffice-devel
Subject:    Re: LZW compression?
From:       Nicolas Goutte <nicog () snafu ! de>
Date:       2002-01-15 20:36:01
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On Tuesday 15 January 2002 20:08, David Faure wrote:
> On Tuesday 15 January 2002 18:01, Michael Marcucio wrote:
> > From: David Faure <david@mandrakesoft.com>
> >
> > >Anyway, the powerpoint->kpresenter filter is at a very rudimentary
> > > stage, and
> > >I doubt the problem you're seeing is related to any kind of compression,
> > >rather to the fact that this filter needs much work AFAIK.
> >
> > you are absolutly right about the filter being in a pre-alpha stage of
> > development (hopefully thats where i come in;). as i was happily parsing
> > each of the containers that were coming back from the file, i get this
> > container that (well in the ms documention) says it contains a lzw
> > compressed docfile which contains the ole object data.  this is where the
> > the filter chokes most of the time. anyway, i figured since i was already
> > here i would try to decompress the docfile. if it turns out i don't need
> > the info i will be more than happy to skip it!
>
> Ah, I didn't understand that you were actually working on the filter, sorry
> ;) Very good ;)
> [I have added you to the posters list, no more moderation queue ;)]
>
> About LZW:
> * with GIFs, it's writing GIF that's forbidden, not reading GIFs, so
> decompressing LZW data shouldn't be a problem

Nobody guarantees it!

For GIF, there are aggreements between Compuserve and Unisys.

I suppose that Microsoft has a licence to use LZW, but who knows how this 
licence or aggreement looks like.

> * AFAIK, LZW is a variation of LZ77 - it would be interesting to know if an
> LZ77-decompressor (like zlib, though zlib is LZ77+Haufmann) can open LZW
> data.... hmm, probably not.

No, they are different (or the patent would be also for LZ77.)

Have a nice day/evening/night!
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