BRDFBTDFModellen

BRDFBTDFModellen is a family of material models used in computer graphics to describe how light interacts with rough, possibly translucent surfaces by combining reflection and transmission components within a single framework. It extends the separate concepts of BRDF (reflection) and BTDF (transmission) into a unified description of light transport at interfaces.

In this modeling approach, the reflected component BRDF(i, o) and the transmitted component BTDF(i, o) are typically derived from microfacet theory, sharing a common microfacet distribution D(h), a Fresnel term F, and a geometric attenuation function G. The transmitted part accounts for refraction according to Snell’s law and indices of refraction, while the reflected part uses Fresnel terms to partition energy between reflection and transmission.

The BRDFBTDFModellen emphasizes energy conservation and reciprocity; the sum of reflected and transmitted flux over all outgoing directions equals the incident flux, and the model aims to be physically plausible for physically based rendering. Achieving this balance often involves careful tuning of D, F, and G and correct normalization between the BRDF and BTDF components.

Applications include modeling glass, water, translucent plastics, and coatings on metals, where both surface gloss and internal attenuation influence appearance. The model captures phenomena such as Fresnel tinting at interfaces, total internal reflection, and the angular variation of reflectance and transmittance.

In practice, BRDFBTDFModellen is used in path tracing and other Monte Carlo rendering methods. The same microfacet parameters may govern both components, with differences arising from how refraction is treated and how energy is distributed between reflection and transmission, enabling coherent and realistic light transport at rough boundaries.