Summary
This work presented three approaches for modeling imperfections and weathering effects.
The first by Becket and Badler[1] just dealt with algorithmically created textures that were mapped on surfaces.
These textures have been created by rule based or fractal algorithms and simulated two dimensional imperfections
like stains and splotches. The whole approach involved two steps. The first step treated the modeling of a
localized instance or concept of a blemish. This included the usage of several fractal and rule based algorithms.
The second and last step concentrated on the placement of the first created instances. Two placement strategies
for simple blemish types where presented.
The second approach by Miller[2] introduced methods to compute the accessibility of surface regions.
These non-accessible regions tend to retain tarnish and dust. To treat these effect convincingly accessibility
has to be computed correctly. This work dealt with two methods for computing the accessibility of a surface.
Tangent sphere accessibility defines the accessibility to a the radius of a sphere which may touch the surface
tangentially and not intersect any other surfaces. Offset distance accessibility considers the accessibility
equal to the distance to the nearest point on an offset of the surface, minus the offset radius.
The third approach by Hanrahan and Dorsey[3] concentrated on metallic patinas and used methods for computing the
accessibility to vary the patina spatially. Some operators where introduced to simulate the process of patina
growth, that proceeds in a system of distinct layers. Methods to modulate these operators across a surface where
presented. This approach also included a simple scrip language that is used to described the sequential application of these operators.
References
[1] Becket W., Badler N. I. Imperfection for Realistic Image Synthesis. The Journal of Visualization and
Computer Animation Vol. 1: 26-32 (1990)
[2] Miller G. Efficient Algorithms for Local and Global Accessibility Shading. Computer Graphics Proceedings,
Annual Conference Series: 319-326 (1994)
[3] Hanrahan P., Dorsey J. Modeling and Renderin of Metallic Patinas. Computer Graphics Proceedings, Annual
Conference Series: 387-396 (1996)