The joint reconstruction of shape and appearance for translucent objects from real-world data poses a challenge in computer graphics, especially when dealing with complex layered materials like leaves or paper. The traditional assumption of diffuse transmittance falls short, and more accurate Monte-Carlo-based models are often needed to reproduce their appearance. To accurately capture the translucent appearance, an acquisition system needs to be carefully designed.

Many animals exhibit structural colors, which are often iridescent, meaning that the perceived colors change with illumination conditions and viewing perspectives. Biological iridescence is usually caused by multilayers or other periodic structures in animal tissues, which selectively reflect light of certain wavelengths and often result in a shiny appearance - which almost always comes with spatially varying highlights, thanks to randomness and irregularities in the structures.

We present a practical analytic BRDF that approximates scattering from a generalized microfacet volume with a von Mises-Fischer NDF. Our BRDF seamlessly blends from smooth Lambertian, through moderately rough height fields with Beckmann-like statistics and into highly rough/porous behaviours that have been lacking from prior models. At maximum roughness, our model reduces to the recent Lambert-sphere BRDF.