ddisimo@encore.com (Darrin DiSimo) (07/05/90)
Hi,
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.
Thanks a lot in advance.
Darrin.twegner@mwunix.mitre.org (Timothy Wegner) (07/06/90)
ddisimo@encore.com (Darrin DiSimo) writes: > 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. GIF files already use LZW compression, which is why ARC, ZIP etc. don't have much if any effect (they all use basically the same method). What we need is a better method. Obviously there is room for improvement. For example, a GIF image of a Mandelbrot set should be compressible 50% just by making use of the symmetry of the image with respect to the X axis. LZW compression doesn't pick that up.
west@gsrc.dec.com (Jim West (Stealth Contractor)) (07/11/90)
In article <127225@csb8.encore.com>, ddisimo@encore.com (Darrin DiSimo) writes... -Hi, - - 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. - - Thanks a lot in advance. - Darrin. Based on my rudimentary knowledge of the LZ compression algorithm, which is what GIF uses, I don't think you will find anything to compress the files any smaller than they are now. ---------------------------------------------------------------------- Jim West | The Schainker Converse west@gsrc.dec.com | to Hoare's Law : | These are my opinions. | Inside every small problem Digital has no idea | is a larger problem struggling what I'm saying. | to get out. ----------------------------------------------------------------------
lowey@herald.usask.ca (Kevin Lowey) (07/11/90)
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
prs@io.UUCP (Paul Schmidt) (07/13/90)
GIF files are _already_ compressed, possibly a run-length encoding; I forget. In fact, if you try to compress them with something like ZIP or ARC, many times they will get larger.