for 24 to 16 no idea come to mind... For 24 to 8 bit.. ya..you are right I have to iterate and find out about color usage, that's already going in my mind, For 256 colors we can make 216 colors by combinations of(0,51,102,153,204, 255)and other 40 colors I have not found yet..how to find these.. But I don't think, it's a good idea. I m working in this direction..but mind is still trying to avoide this method. Regards, Sumit K sumit_kapoor1980@hotmail.com