Physically Based Rendering of Corroded and Aged Surfaces

Bernhard Spatzek


The precision of image synthesis techniques for rendering naturalistic scenes often works contrary to the realism of the everyday world. Many computer generated images can be described as uniform and perfect, because the surfaces are smooth, neat and crisp in appearance. Efforts to produce realism have recently focused on light and interaction of light with surfaces. The radiosity methods have shown that proper treatment of light is often critical to the proper visual effect in an image. Even the best of these images is nearly surrealistic in its precision, and thus belies its synthetic origins. A careful examination of the real world, however, yields more dimensions to the quest of realism than lightning models. Image synthesis techniques also require geometric models and surface reflectance models that incorporate accurate physical material properties and their response to light. These are critical to the microscopic generation of the correct light reflectance. But the present state of modeling even fails to account for an important macroscopic dimension of realism in computer synthesized images: real objects are dirty.

This work deals with three approaches for adding 'imperfections' to a surface.
The first by Becket and Badler[1] concentrates on algorithmically created textures that are mapped on the surfaces. Their goal is to achieve a more natural appearance by modeling the kinds of surface features the do not intrinsically deform the surface geometry.
The second approach by Miller[2] discusses several methods for computing the accessibility of a surface. Also the visual effect of shading using accessibility is shown to resemble the patina of certain tarnished surfaces which have then been cleaned.
Finally the third approach by Dorsey and Hanrahan[3] deals with weathering effects, the modeling and rendering of metallic patinas. Where a patina is a film of incrustion on a surface that is produced by the removal of material, the addition of material, or the chemical alternation of a surface. A technique to model and render patinas of copper and copper alloys is introduced.

Continue with An Approach for Modeling Dirtyness.