A fiber scattering model with non-separable lobes

Abstract

Figure 1: Glossy reflections from fibers exhibit a lightand view-dependent lobe tightening similar to surface reflectance that previous analytic fiber models lack (a,c). We derive new non-separable fiber-scattering lobes that exhibit this and additional behaviours seen in ground-truth simulation of rough dielectric fiber scattering. Parameter tweaking of previous models can produce results similar to (d), but no previous model with fixed settings can simultaneously produce both (b) and (d). We found that ground-truth renders using explicit cylindrical geometry with Cook Torrance reflectance to be indistinguishable from (b) and (d) (upon convergence, which required significantly more samples per pixel). The difference between the old and new models is further illustrated in (e) by visualizing the R lobe of a circular fiber with Beckmann micro roughness and tilted scales (black hair). In the backlit case (c,d) light grazes the edges of fibers and exhibits the brighter more focused response (seen in (e) where the lobe compresses and brightens for high |φ |).