I would like to be able to change the color scheme of my website.  I
have about 1000 GIF files,  many with antialiased text.  Although the
majority of the files are buttons with two colors,  I can't simply
change the 2 colors in the GIF's color table because the antialiasing
averages the pixels on the boundary between the text and the
background.  This means I have to figure out what colors to assign the
antialiased pixels in the new site.

Is there a way to calculate what the antialiased colors will transform
to in the new image,  if I know what the before and after RGB colors
of the text and background are?

I would love it if a tool would do this for me,  but if there's some
vector equation I could use that to calculate this that would be great
too.

Hello Amped02139,

The effect when changing your background-color without adapting your
transparent GIFs is usually called "halo" or "ghosting". In the future
you might want to save the original file from your photo-retouching
program before exporting to GIF, or explore possibilities of the PING
file format. Admitted, those two suggestions won't help you now!

What I would so is fire up Corel Photo-Paint, and use the filler tool
on the old background to fill it with the new background, but using
the smoothing options so that it also goes over the border. You can
record a macro, and write a Corel-Script around it, which can now act
like a batch file going over all the files. Creating the original
effect would take some trial-and-error until you find the right
tool-settings.
Also, you might want to try a color mask with smooth edges, and then
use the filler tool.

Note that when you want to have the best effects, you should increase
the colors in Photo-Paint before working with the image, and
afterwards, decrease them again (e.g. from 8-bit to 24-bit to 8-bit
colors again).

Hope this helps!

j_philipp-ga, 

Thanks for the comment.  Your suggestion would help change the
background (and I could repeat the process for the font foreground), 
but I suspect that smoothing/blurring the edges wouldn't give me the
same effect as anti-aliasing (or would take a lot of trial/error). 
And yes,  the folks who did the original graphics and could have saved
things as layers are long gone :-).

If you look at the image palette for most images,  there's only about
15 different colors.  It's pretty easy to programmatically cycle the
palette,  so I guess I'm looking for help writing the formula to do
that.