Rendering the Appearance of Aging Materials

Computer graphics is used in a wide variety of familiar applications, ranging from abstract representations of statistical and scientific data to synthetic characters in feature films and games. One important sub-area of computer graphics is the generation of realistic images. A key component in generating realistic images is creating digital models of the appearance attributes of the materials used in the scene being simulated. A variety of methods for modeling the attributes of pristine homogeneous materials have been developed in computer graphics over the past 30 years. However, many applications require simulating materials that have undergone spectral, spatial, and directional changes due to weathering and usage. In applications, realistic images may be either required to be plausible or predictive. To be plausible, images must appear to an observer to be indistinguishable from a photograph of a physical scene, although the observer never needs to make a critical decision based on the image. Many applications such as computer games or synthetic props in film require only plausibility. To be predictive, images must appear the same to an observer as an image acquired of a physical scene. Unlike plausible images, predictive images are used by observers to make decisions, such as selecting a design or training for a task that requires target visibility. Methods for generating predictive images are based on physical models derived from work in other disciplines, and are subject to validation Chapter 19