A combined scattering and diffraction model for elliptical hair rendering

Abstract

Realistic hair rendering relies on fiber scattering models. These models are based on either ray tracing or on full wave‐propagation through the hair fiber. Ray tracing can model most of the scattering phenomenon observed but misses the important effect of diffraction. Indeed human natural hair specific dimensions and geometry demands for the wave nature of light to be taken into consideration for accurate rendering. However, current full‐wave model requires nonpratical, several days precomputation, that needs to be repeated for every change in the hair geometry or color, for appropriate results. We present in this paper a dual hair scattering model which considers the dual aspect of light: as a wave and as a ray. Our model accurately simulates both diffraction and scattering phenomena without requiring any precomputation. Furthermore, it can simulate light transport in hairs of arbitrary elliptical cross‐sections. This new dual approach enables our model to significantly improve the appearance of rendered hair and qualitatively match scattering and diffraction effects seen in photos of real hair while adding little computation overhead.

A Microfacet‐based Hair Scattering Model

“…However, the mean diameter of human hair is 80 µm [DK04], at which scale diffration is present. It would be interesting to trace complex rays with our method, similar to Benamira and Pattanaik's method [BP21].…”

Chemomechanical simulation of soap film flow on spherical bubbles

“…The key changes lie in adjusting the differential surface area element da m and the projected area in the outgoing direction a ⊥ o . We demonstrate the necessary modifications for elliptical cross-sections, as real hair fibers are often roughly elliptical [11,66]. After replacing these terms in the above derivation, we arrive at the BCSDF for elliptical fibers…”

“…The importance of elliptical hair fiber cross-sections has been pointed out and a specialized azimuthal scattering function has been devised to this end [66]. The model has even been extended to include certain effects of diffraction [134,11], while still keeping the original assumption of longitudinal/azimuthal separability. We do not consider wave-optics in this work.…”

Visual simulation of opal using bond percolation through the weighted Voronoi diagram and the Ewald construction

“…Nagata et al [40] proposed a method for multilayer thin-film interference in pearl, while Sun [51] introduced a model that considers both diffraction by microstructures and interference by multilayer thin films to reproduce the structural colors found on insects. Guillen et al [19] presented a generic model to reproduce pearlescent materials, and Benamira and Sumanta [5] focused on diffraction-aware hair rendering. Further, Huang et al [24] developed a model to compute the structural color of the feathers on pigeon necks, and Guo et al [20] proposed a light-scattering model that pre-computes and considers diffraction and interference by nearby particles in participating media.…”