Fast, Soft Reflections Using Radiance Caches

Apurva Shah, Justin Ritter, Chris King, Stefan Gronsky

Abstract:

In Pixar's Ratatouille a lot of scenes take place inside the kitchen where reflective surfaces like counter tops, stoves, pots and pans abound. Furthermore, these surfaces were often burnished or covered with dents, scratches or other displacements, which meant that the reflections were soft and fuzzy. Physically accurate reflections are most often achieved by tracing reflected rays into the scene. When the ray encounters another object, computationally expensive lighting and shading calculations must be performed to determine the contribution of the reflecting point. Paradoxically, surfaces that have soft or fuzzy reflections are more expensive since they have a larger reflection cone angle requiring more rays to adequately sample the reflected scene. We present a technique that utilizes radiance caches to significantly speed up the reflection calculations and discuss some of the accuracy trade-offs inherent to this approach.

Available as Pixar Technical Memo #07-04