1. A method of improving a characteristic of an image according to its material content, said method comprising the steps of: providing an image comprised of image pixels; generating a belief map corresponding spatially to the image pixels, wherein the belief map includes belief values indicating the likelihood that respective pixels are representative of a particular material; generating an improvement parameter from the belief values of the belief map, wherein the improvement parameter is proportional to the belief values and applied uniformly to the image pixels; and using the improvement parameter to improve the characteristic of the image.