8 - Aging and weathering

Abstract

Materials have a temporal, as well as a spatial, dimension. Material appearance depends on the history of usage and environment and the basic chemical components and surface finish. Materials may be purposefully treated to achieve particular end results or may change as the result of natural aging or weathering. This chapter presents methods that either simulate temporal evolution of changes in materials or directly model the visual results of processed materials. Real materials frequently change in appearance with time as a result of their interaction with the surrounding environment. For a particular object composed of a given material, the rate and extent of change are dependent on the shape of the object, its exposure to the surrounding environment, and the properties of the material of which it is composed. Much of the visual richness of natural scenes is due to the patinous action of the environment, resulting in such looks as lichen-covered stonework or silver-gray cedar boarding. Such changes in appearance are generally termed aging or weathering. Modeling appearance variations associated with aging is critical to generating input for realistic scenes. It begins with a taxonomy of aging effects. Next, look at the two primary ways to generate weathering effects: simulation and replication. It concludes with a survey of recent work on capturing real aging effects and transferring them to synthetic shapes.