An efficient and practical near and far field fur reflectance model

Abstract

Physically-based fur rendering is difficult. Recently, structural differences between hair and fur fibers have been revealed by Yan et al. (2015), who showed that fur fibers have an inner scattering medulla, and developed a double cylinder model. However, fur rendering is still complicated due to the complex scattering paths through the medulla. We develop a number of optimizations that improve efficiency and generality without compromising accuracy, leading to a practical fur reflectance model. We also propose a key contribution to support both near and far-field rendering, and allow smooth transitions between them. Specifically, we derive a compact BCSDF model for fur reflectance with only 5 lobes. Our model unifies hair and fur rendering, making it easy to implement within standard hair rendering software, since we keep the traditional R, T T , and T RT lobes in hair, and only add two extensions to scattered lobes, T T s and T RT s. Moreover, we introduce a compression scheme using tensor decomposition to dramatically reduce the precomputed data storage for scattered lobes to only 150 KB, with minimal loss of accuracy. By exploiting piecewise analytic integration, our method further enables a multi-scale rendering scheme that transitions between near and far field rendering smoothly and efficiently for the first time, leading to 6 − 8× speed up over previous work.

A combined scattering and diffraction model for elliptical hair rendering

“…D'Eon et al [dFH*11], offered a new energy‐conserving longitudinal scattering function, a new simple way to sample the hair scattering function [dMH13] and a new non‐separable longitudinal scattering function which takes into account the azimuthal angle when computing the longitudinal function [dMH14]. To accurately model fur, Yan et al extended the circular dielectric cylinder model by including a second cylinder concentric to the first one [YTJR15] [YJR17]. The latter model can also be used to render hair.…”

A practical ply-based appearance model of woven fabrics

“…Fiber scattering models. The reflectance profile used by our technique is related to various fiber [Aliaga et al 2017;Khungurn et al 2016;Marschner et al 2003;Zinke and Weber 2007] and fur [Yan et al 2017[Yan et al , 2015 2006; Moon et al 2008;Zinke et al 2008]. These models utilize bidirectional curve scattering distribution functions (BCSDFs) to describe how light scatters off individual fibers or fur strands.…”

“…To simulate how light is scattered by the generated ply-level geometry ( §3) we build on recent work on appearance modeling of hair and fur [d'Eon et al 2011;Yan et al 2017;Zinke and Weber 2007]. One major difference to hair and fur rendering is that we compute light scattering with an aggregate bundle of cloth fibers rather than considering how light is scattered by each individual fiber.…”

“…Although this is a rough approximation to the true single-and multiple-scattering phenomenon, we find it adequate in practice since cloth fibers are usually disorganized, causing light to diffuse quickly inside a ply. A similar approach was used byYan et al [2017] to account for scattering by the medulla in fur.ACM Trans. Graph., Vol.…”

Real‐Time Rendering of Wave‐Optical Effects on Scratched Surfaces

“…Rendering scratches and line‐like features such as fibers [dMH13] or hair [dFH*11, YJR17] are closely related due to the common geometrical properties. Recent models for reflection from worn surfaces are limited to geometrical optics and represent scratches using scratch profiles made of aligned surfaces with associated procedural BRDFs, their positions described by curves on the surface [BPMG04].…”