2008.12.19 03:59 "Re: [Tiff] Project on .bmp to .gif", by Bob Friesenhahn

      I think to convert this 24 bits data,for this we uses color table
but how we make it ,how many enteries it contains.is 8 bits enteries
is sufficient for this? How is the approximation done in case when
the color table is full and there are still more colors left in the
image?

This is how it is done in GraphicsMagick and ImageMagick:

   http://www.graphicsmagick.org/quantize.html

The algorithm is not specific to TIFF.

The 'tiffmedian' utility comes with libtiff and provides a fast way to reduce colors using a different algorithm.

Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/