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From: lowey@herald.usask.ca (Kevin Lowey)
Newsgroups: alt.graphics.pixutils,comp.graphics
Subject: Re: Compressing GIF images
Message-ID: <1990Jul11.151745.12737@dvinci.usask.ca>
Date: 11 Jul 90 15:17:45 GMT
References: <127225@csb8.encore.com>
Sender: news@dvinci.usask.ca
Reply-To: lowey@herald.usask.ca
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Organization: University of Saskatchewan
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From article <127225@csb8.encore.com>, by ddisimo@encore.com (Darrin DiSimo):

>     I was wondering if anyone knows of a PD compression
> program for GIF files.  Gif files are taking up a lot of disk
> space and I know regular compression does not work.

You won't be too successful.  .GIF files already are compressed with LZW 
compression, which is one of the most efficient compression schemes in 
popular use today.  Other compression methods may give you marginally smaller
files (like less than 5% smaller) which is hardly worth the effort.

The reason for the built in compression is that GIF files were originally
designed by Compuserve as a method of viewing bitmapped images "on-line".
Thus they wanted something to minimize file transfer time.  

Related to this is the GIF "interlaced" mode, which covers the screen in 
four passes.  It allowed an on-line user to get an overall coarse view of 
the image that then gets refined in four passes.  That way the on-line user 
could cancel the image once he has seen enough instead of waiting for the 
entire image.

- Kevin Lowey