transgif

 Usage:
      transgif -in pic1.gif [pic2.gif ....]
   or
      .... | transgif [options] | ....
   or
      transgif [options] regular.gif > transparent.gif

 Normally used as
      transgif -in pic.gif
 the "-in" means to update the gif in place. You can list as many files
 as you like.

 If there are no files given, transgif filters STDIN to STDOUT.
 In this case, STDIN should be one gif.

 If there is exactly one file, a modified version is spit to STDOUT.
 This is rather odd (it'd be nice if it was done in-place, with a special
 option to have it spit to stdout), but is a throwback from the first
 version I whipped up for the old comp.infosystems.www (back when it
 existed)
 
 For each picture, the default is that whatever color happens to fall
 into the first colormap slot (often black) will be made transparent. 
 This can be changed via the the options.

 The options are from:
   -p              print the colormap (to STDERR).
                   The new gif still goes to STDOUT.

   -###            make colormap index-### transparent (default is -0)

   -rgb ## ## ##   Take the three numbers as R G B values (in the range
                   of 0..255 (or 0x00..0xff). The first colormap entry
                   with those RGB values is made transparent.

   -rgb name       Use the R G B values of the color 'name' if known
                   by this program (data from X11's rgb.txt)

   -help           show a short help message and exit.

   -in             [not an regular option, but listed here because it
                   looks like one]. Says to transform each gif in
                   place. Happens automatically if more than one gif
                   is given.

 I wrote this because people ask for something like this all the time.
 I just learned the format of GIFs a week ago, so this will likely be
 lacking in many respects. Still, from what I hear people find it useful.