Importance Sampling of Reflections from Hair Fibers

Christophe Hery, Ravi Ramamoorthi

Abstract:

Hair and fur are increasingly important visual features in production rendering, and physically-based light scattering models are now commonly used. In this paper, we enable efficient Monte Carlo rendering of reflections from hair fibers by describing a simple and practical importance sampling strategy for the reflection term in the Marschner hair model. Our implementation enforces approximate energy conservation, including at grazing angles by modifying the samples appropriately, and includes a Box-Muller transform to effectively sample a Gaussian lobe. These ideas are simple to implement, but have not been commonly reported in standard references. Moreover, we have found them to have broader applicability in sampling surface specular BRDFs.

A revision of this work was accepted as the first paper in the Journal of Computer Graphics Techniques, and available as http://jcgt.org/published/0001/01/01/.

Available as Pixar Technical Memo #11-07