(keitai-l) Re: keitai-l Digest V2 #109

I wrote an icon editor called "IconPainter" that
creates the non-LZW GIF's described (it's on my
website at www.cellspark.com ). The only problem is I
couldn't get the GIF coder I wrote to work with more
than 128 colors. I'm not sure if non-LZW is possible
with more than 128.

I disagree with the the assertion that there is no
non-LZW GIF. What you do is have an empty dictionary
when you code so the bytes are essentially run length
encoded since there is no substitution of symbols
going on. The LZW algorithm isn't used but the decoder
doesn't care. Since no dictionary is created it just
outputs each byte as it comes to it as is. The whole
symbol substitution process that is the core of LZW is
bypassed. For small GIF's like those found on i-mode
phones the size penalty is suprisingly small.

Luckily Unisys's patent expires next year so we won't
have to worry about it much longer. (can I also add
that I think LZW is one of the most elegant algorithms
I've ever come across).

Regards Colin Mummery
www.cellspark.com

 --- keitai-l@appelsiini.net skrev: > keitai-l Digest
Thu, 23 May 2002	Volume: 02  Issue:
> 109
> 
> In This Issue:
> 		GIFs and life
> 		Re: GIFs and life
> 
>
----------------------------------------------------------------------
> 
> From: "Paul Hardy" <pjh@bushcat.com>
> Subject: GIFs and life
> Date: Thu, 23 May 2002 20:19:41 +0900
> 
> 
> 
> I'm sure this is an old topic but I can't find it:
> 
> What tools, if any, are people using to create
> non-LZW GIFs? Can all phones
> cope with REL-encoded GIFs, or must they be
> uncompressed, if not LZW'd?
> 
> 
> ------------------------------
> 
> Date: Thu, 23 May 2002 18:26:53 +0100 (GMT Daylight
> Time)
> From: Ben Hutchings <ben.hutchings@roundpoint.com>
> Subject: Re: GIFs and life
> 
> 
> 
> On Thu, 23 May 2002, Paul Hardy wrote:
> 
> >
> > I'm sure this is an old topic but I can't find it:
> >
> > What tools, if any, are people using to create
> non-LZW GIFs? Can all phones
> > cope with REL-encoded GIFs, or must they be
> uncompressed, if not LZW'd?
> 
> The GIF format requires that pixel data be stored as
> an LZW stream; there
> is no option to specify any other encoding. 
> However, it is possible for a
> encoder that doesn't use the LZW algorithm to
> produce inefficient but
> valid LZW streams.  I'd not heard of RLE GIFs, but I
> suppose you could
> make an RLE encoder generate an LZW stream.  A web
> search turned up
> references to several tools that do that.
> 
> Any phone should be able to cope with a GIF that
> wasn't produced by a true
> LZW encoder, because it's in exactly the same
> format.
> 
> 
> ------------------------------
> 
> End of keitai-l Digest V2 #109
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