Bidirectional reflectance distribution function

A bidirectional reflectance distribution function (English Bidirectional Reflectance Distribution Function, BRDF ) is a function of the reflection behavior of surfaces of a material under arbitrary angles of incidence Represent supplies for each impinging on the material light beam with a given entry angle of the ratio of radiance and irradiance for each outgoing light beam. BRDFs are used inter alia in the realistic 3D computer graphics, where they constitute a fundamental part of the rendering equation and are used to represent surfaces as realistic and physically correct. A generalization of the BRDF to textures, the BTF ( Bidirectional Texturing Function) dar.

A BRDF is very complex depending on the chosen accuracy: it can, for example, for all Einfalls-/Reflexionswinkel (4- dimensional), for each wavelength (5- dimensional) or be determined for each point of the surface (7- dimensional). Due to this complexity, as BRDFs usually simple model used in the computer graphics.

Formula:

There are basically two approaches to the representation of the BRDF values:

  • ( by a gonioreflectometer obtained, for example ) explicit storage of the parent values ​​or simulation results, high memory space requirement for easier storage in finely divided samples,
  • Poorly suited for importance sampling,
  • Important for verification tasks,

Physically correct BRDF

The BRDF of a real object must also possess the following properties:

  • Positivity:
  • Satisfies the Helmholtz reciprocity:
  • Conservation of energy:
Bidirectional texture function Subsurface scattering
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