Re: .gif rot

["Jens B. Jorgensen" <jjorgens@bdsinc.com>]

Ralph Winslow wrote:
> 
> After X has run for awhile, I notice a substantial degradation in the
> quality of the .gif images that I display.  There might also be a bit of
> decline iin the image quality of the .jpg images as well.  I've decided
> to spring for the $20 that another Mb of Vidcard memory will set me
> back, but should I expect it to help, or is there some other path I
> might check out?  TIA for any clue.
> --
> -----------------------------------------
> Ralph Winslow                 rjw@nac.net
> Someday soon I really  MUST find a way to
> piss away a LOT of bandwidth on this .sig
> 

I can't give you a definitive answer because this isn't my area of
expertise, but I'm pretty sure I know what this is. First, you must
be running your X server at 8 bits-per-pixel. At this depth, you
naturally can only display 256 colors on the screen at a time (although
those colors can be pretty much anything). Viewers such as xv will
try to allocate as many colors from the color map as possible in order
to best display the image. Then later on the cells of the map don't
get deallocate so when another image is going to be displayed there
aren't colors left to use. The alternative is to have the program
(this works for netscape and xv) use a private color map. "Why don't
they do this all the time by default?" you ask? Well, for one it
uses resources (and you don't need it with a 16-bit or higher
color-depth because you can always display "all colors"). For two,
it makes it so that when you switch windows you get this funny 
change in the colors of your windows since changing the color map
actually reloads the palette in your video card suddenly color
0xc5 is no longer "sea azure", now it's "psycho magenta". Of course
if you're trying to view a photo-derived GIF at least now you can
see the picture. When the window loses focus the colors shift back.

Now, maybe you already knew the above and perhaps you're already 
passing the '-install' parameter to Netscape and it *still* has 
image degradation over time. If this is the case then I guess 
Netscape must not be changing its own color map for each new picture
but just allocating cells until they're gone and then using the
"closest" colors available after that. If this is the case it's a
bug in Netscape.

I think all this is correct, however I make no warranties, express
or implied, as to the usability of the above information or its
fitness for a particular purpose... 8)

-- 
Jens B. Jorgensen
jjorgens@bdsinc.com


--
TO UNSUBSCRIBE FROM THIS MAILING LIST: e-mail the word "unsubscribe" to
debian-user-request@lists.debian.org . 
Trouble?  e-mail to templin@bucknell.edu .