Can you explain this in better detail, perhaps with an example. The first thing that comes to my head, from IDL's use of DECOMPOSE in a Direct Graphics DEVICE procedure keyword, is that you have an image that is based on a 256-element color table, and you would like to convert it to its true color equivalent. I am also not sure what you mean by the "coefficients" of an image. Do you mean the values of each pixel in the image? And, if yes, do you mean values in terms of an index to a color table or values in terms of the Red/Green/Blue intensity that is stored for every pixel? James Jones