instead of trying to minimize some cost function of color errors , the present invention exploits physical models of scene - image relations . an image is first segmented into regions corresponding to objects in the physical world . each object is then painted with a few levels of shades of the same chromaticity . this is motivated by the observation that physical objects are the basic units for human visual perception . chromatic variations within an object surface tend to be grossly discounted by our color vision , and therefore , it is not necessary to render those variations accurately . furthermore , since the shading across an object surface spans a much smaller dynamic range as compared to the whole scene , the limited number of color shades can be more effectively used within a segmented image region .