BRDFbased

BRDFbased refers to methods and models that rely on the Bidirectional Reflectance Distribution Function to describe how light reflects at a surface. The BRDF links incoming light direction ω_i and outgoing direction ω_o to reflected radiance; it is defined for opaque, homogeneous surfaces and is constrained by reciprocity and energy conservation.

The reflected radiance L_o(ω_o) is given by L_o(ω_o) = ∫_Ω L_i(ω_i) f_r(ω_i, ω_o) cos θ_i dω_i, where θ_i is the angle between ω_i and surface normal. In practice, the f_r is often assumed to be a function of directions in a local frame, independent of position for a homogeneous material. Evaluation can be analytic or via sampling; many BRDFs are directional but locally stationary.

Common BRDFs include Lambertian diffuse f_r = ρ_d/π; specular or microfacet models like Cook-Torrance, which decompose f_r into a microfacet distribution D(h), Fresnel term F, and geometric term G. Real materials frequently combine diffuse and specular terms and may include anisotropy. BRDF-based models are used to simulate a wide range of appearances, from shiny metals to rough plastics.

BRDF-based shading is central to physically based rendering, enabling energy-conserving, view-dependent reflections. It supports material synthesis, rendering realism, and inverse BRDF estimation. Data-driven BRDFs use measured reflectance to fit models, improving realism in either synthetic scenes or real-world material capture.

Measured BRDFs are available in databases such as MERL; BRDF modeling must handle roughness, anisotropy, and wavelength dependence. In computer graphics, performance considerations drive techniques like importance sampling and precomputation to achieve real-time or interactive rendering with BRDF-based materials.