ISHair: Importance Sampling for Hair Scattering

Abstract

We present an importance sampling method for the bidirectional scattering distribution function (bsdf) of hair. Our method is based on the multi-lobe hair scattering model presented by Sadeghi et al. [SPJT10]. We reduce noise by drawing samples from a distribution that approximates the bsdf well. Our algorithm is efficient and easy to implement, since the sampling process requires only the evaluation of a few analytic functions, with no significant memory overhead or need for precomputation. We tested our method in a research raytracer and a production renderer based on micropolygon rasterization. We show significant improvements for rendering direct illumination using multiple importance sampling and for rendering indirect illumination using path tracing.