The next step in creating more realistic computer - generated images is the development of better models of the physical structures of materials and their degradation by the environment

tertainment milestone in 1995 with the release of Toy Story, the first full-length movie animated using computers. But the digitally created characters and sets of such productions generally still have a distinctive look that sets them off from reality: everything is a little too smooth and perfect, a little too clean, as if freshly molded in plastic. What’s missing is dirt and dust, cracks and scratches; a dribble of rust down a wall from a leaky pipe; a patchy green patina of oxidation on a copper statue; the salt-crusted, weather-beaten face of an ancient granite sphinx; the fine tones of human skin, complete with freckles, pores, wrinkles and a slight flush of living blood. The Pixar team, which released Toy Story 2 late last year, does add weathering effects such as scuffs and dirt by painting patterns onto surfaces, but this process is ad hoc and very time-consuming. More intensive application of these established techniques or brute-force application of greater computing power will not be enough to overcome the cartoonish, waxen look of computer graphics. To produce a simulation that doesn’t look like one, we must properly model the appearance of materials in all their variety, including realistic wear and grime. Techniques such as ray tracing and radiosity, which simulate lighting, can add to the ambience of virtual scenes with effects such as soft shadows and reflections, but the accuracy and visual complexity of the resulting images also depend crucially on the quality of the underlying material models. Such models are becoming increasingly realistic. An important feature of them is explicit modeling of a material’s Digital Materials and