A Practical and Controllable Hair and Fur Model for Production Path Tracing

Abstract

We present an energy-conserving fiber shading model for hair and fur that is efficient enough for path tracing. Our model adopts a near-field formulation to avoid the expensive integral across the fiber, accounts for all high order internal reflection events with a single lobe, and proposes a novel, closed-form distribution for azimuthal roughness based on the logistic distribution. Additionally, we derive, through simulation, a parameterization that relates intuitive user controls such as multiple-scattering albedo and isotropic cylinder roughness to the underlying physical parameters.

An efficient and practical near and far field fur reflectance model

“…Improved accuracy and practicality: We improve the accuracy of the model by considering different roughnesses of azimuthal and longitudinal sections, as has been observed in previous studies (Chiang et al 2016;d'Eon et al 2011). Moreover, we find that the medulla is not purely scattering, and can also absorb light (Carrlee and Horelick 2011).…”

“…However, their computational cost of evaluation is significant, using Gaussian quadrature and Taylor expansion. Chiang et al (2016) adopted a near-field formulation by considering accurate incident positions azimuthally, leaving expensive integration across the entire azimuthal section to the renderer. In summary, apart from the original Marschner model that is not physically correct, there are no efficient closed-form solutions for azimuthal integration.…”

“…Figure 7 demonstrates that the medulla can absorb light because of its complex internal structure, and that there are cases where pigments are found within the medulla (Carrlee and Horelick 2011). We also take different longitudinal/azimuthal roughness into account, since these differences are often observed (GalatÃŋk et al 2011) and used in practice (Chiang et al 2016;d'Eon et al 2011). Table 1 lists all the parameters used in our model, Fig.…”

“…The Marschner model assumes that the azimuthal section is perfectly smooth, thus leading to an analytic solution. However, azimuthal roughness has been demonstrated to be important (Chiang et al 2016;d'Eon et al 2011) and should be taken into account for physical accuracy. Unfortunately, with the additional complexity, these models with rough azimuthal sections are no longer analytical for far field approximation.…”

A high fidelity synthetic face framework for computer vision

“…The hair color is represented as three scalars -proportion of melanin, pheomelanin, and proportion of gray hairs. The strand based hair is shaded using a physically based hair shader [3].…”