Optical Parameter Estimation for Hair and Fur using Differentiable Rendering.

In this paper, we propose a parameter estimation method for Bidirectional Curve Scattering Distribution Function (BCSDF) for hair and fur using differentiable rendering. Given fiber geometries, illumination, and a target rendered image, our method jointly estimates optical parameters of BCSDF so as to match the target image taking into account indirect illumination. We develop a differentiable path-tracing renderer tailored to estimate optical parameters of BCSDF. To avoid getting stuck in a local minimum, we propose a two-stage estimation method where the first stage estimates two optical parameters affecting hair and fur’s entire appearance. Then, all the optical parameters are jointly estimated in the second stage. Experimental results substantiate that our method can automatically estimate optical parameters of hair and fur.