Bidirectional texture function

Bidirectional texture function (BTF) <ref name="r3" /><ref name="r4" /><ref name="r1" /> is a 6-dimensional function depending on planar texture coordinates (x,y) as well as on view and illumination spherical angles. In practice this function is obtained as a set of several thousand color images of material sample taken during different camera and light positions.

The BTF is a representation of the appearance of texture as a function of viewing and illumination direction. It is an image-based representation, since the geometry of the surface is unknown and not measured. BTF is typically captured by imaging the surface at a sampling of the hemisphere of possible viewing and illumination directions. BTF measurements are collections of images. The term BTF was first introduced in <ref name="r3" /><ref name="r4" /> and similar terms have since been introduced including BSSRDF<ref name="r5" /> and SBRDF (spatial BRDF). SBRDF has a very similar definition to BTF, i.e. BTF is also a spatially varying BRDF.

To cope with a massive BTF data with high redundancy, many compression methods were proposed.<ref name="r1" /><ref name="r2" />

Application of the BTF is in photorealistic material rendering of objects in virtual reality systems and for visual scene analysis,<ref name="r7" /> e.g., recognition of complex real-world materials using bidirectional feature histograms or 3D textons.

Biomedical and biometric applications of the BTF include recognition of skin texture.<ref name="r6" />

See also

• BSDF == BRDF + BTDF, a 4+1 dimensional function of the scattering distribution from a single point/pixel/vertex.
• Columbia Utrecht Reflectance and Texture Database
• BTF Database Bonn and Measurement Lab
• CVPR 2010 BTF Modeling Tutorial
• BTFbase - BTF compression based on a multi-level vector quantization (free BTF shader)
• UTIA BTF Database - a new source of publicly available bidirectional texture function measurements