The source code looks fine to me. I am focusing on the Mix function for two reasons. First, the rest is over my head. Second, Mix is either generating a good BMP file for "Out.BMP" or it is not. The display on the Tk dialog box is secondary at the moment. If the large image looks ok, then we worry about the Tk dialog. Make sense? So: Anxcon, are the BMP files jacked up? Would you please send one to me at my underdog account at fantasy3d.com? Please send me a Red.bmp, Grn.bmp and Out.BMP so that I can see how they are being incorrectly combined. Yes, I realize you have already done this for Ockham, but as Eric Raymond (?) says, bugs don't last long with 1000's of eyes are looking at them (or pairs of eyes in this case). ===Underdog===