Computer graphics is finding growing application to virtual visual prototyping for the design of materials and products where appearance is important. Using graphics rendering on a display to replace physical prototypes could potentially make it faster and cheaper to bring new products and designs to market. But such applications demand high fidelity in the appearance of specific real materials on displays with ever-higher resolution. The fundamental problem is that current mathematical models for light reflection assume that details smaller than a pixel can be ignored, and replaced by smooth averages. At high resolutions this assumption breaks down; most materials start to appear noisy, grainy, or glittery as one looks closer. But to simply include microscopic detail in the model and continue with conventional rendering methods would be far too slow. This project will develop a range of methods to model the visible effects of sub-pixel details without greatly increasing the time and expense of rendering images. The results of this research will generalize a broad range of material models used in computer graphics so that they work under close-range observation. It will transform the field by fundamentally changing the definition of surface reflectance and by providing a suite of new tools for implementing and designing reflectance in industrial applications including automotive design, virtual prototyping, visual effects, and predictive product visualization.
Accurately rendering the appearance of materials has always been a central problem of computer graphics. With today's ever-higher display resolutions, and applications demanding exact reproduction of specific materials, the status quo in material modeling is reaching its limits. The problem is that the standard approach to modeling surface reflectance, the Bi-directional Reflectance Distribution Function (BRDF), fundamentally assumes that surface roughness is far smaller than the scale of pixels. But rough surfaces, which can be modeled by smooth BRDF models for more distant or lower-resolution views, start to appear noisy, grainy, or glittery as one looks closer and the effects of individual scattering elements become visible. This produces "shimmering" or "glints" in a variety of materials that are difficult to model using current technology, including metallic paints used on cars, bead-blasted and brushed metal finishes popular for electronics, and the ubiquitous textured finishes on injection-molded plastic, as well as in fabrics, wood finishes and wood grain, and many other materials. This project will develop new ways to think about surface reflection in terms of reflectance models that build in spatial and angular variation at their core, without assuming smoothness at small scales. These models account for the visible effects of individual scattering features, and spatial and angular detail emerges naturally as the viewing and illumination conditions reveal it. Several mathematical representations for detailed materials are proposed, covering both surface and subsurface effects, to form the core of a full end-to-end pipeline that spans new acquisition methods and rendering techniques.
