A Physically-Based Reflectance Model For Mammalian Fur Fibers Based On Anatomy And Gonioreflectometry Measurements

Rendering photo-realistic animal fur is of practical importance in many computer graphics applications. In the past, the visual appearance of specific fiber types have been studied, and various reflectance models have been proposed. These models, however, lack either physical accuracy or versatility to produce the wide range of specular and diffusive material properties observed on animal fur fibers in the wild. To uncover the cause of various reflectance phenomena in fur fibers, we make two- dimensional far-field reflectance profile measurements on fur fibers from nine mammalian species and a human hair. Based on the measurements, we reconstruct light paths for all the observed reflectance lobes and devise a physically -based reflectance model for arbitrary mammalian fur fibers. In our model, a fur fiber is represented by two coaxial cylinder volumes, where an outer cylinder represents the biological observation of a cortex covered by multiple layers of cuticle scale, and an inner cylinder represents the scattering interior structure known as the medulla. By running Monte Carlo simulations, we validate that our model preserves high fidelity to actual animal fur and can simulate a large array of microscopic and macroscopic reflectance phenomena. Finally, we develop a practical, near-field shading approach, based on an analysis in scattering paths over the two-dimensional cross section of the coaxial cylinder model. For efficient rendering, we factor reflectance lobes into separated azimuthal and longituindinal profiles, and include a precomputed component for medulla scattering. We verify the accuracy of our approximation scheme, and show that our practical shading model fits the measurement data significantly better than any prior model, and is capable of capturing many characteristic visual features of real fur fiber