Bidirectional texture function (BTF)
is a 6-
dimension
In physics and mathematics, the dimension of a mathematical space (or object) is informally defined as the minimum number of coordinates needed to specify any point within it. Thus, a line has a dimension of one (1D) because only one coo ...
al 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
and similar terms have since been introduced including
BSSRDF 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.
Application of the BTF is in
photorealistic material rendering of objects in
virtual reality
Virtual reality (VR) is a Simulation, simulated experience that employs 3D near-eye displays and pose tracking to give the user an immersive feel of a virtual world. Applications of virtual reality include entertainment (particularly video gam ...
systems and for visual scene analysis,
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.
See also
*
BSDF BRDF
The bidirectional reflectance distribution function (BRDF), symbol f_(\omega_,\, \omega_), is a function of four real variables that defines how light from a source is reflected off an Opacity (optics), opaque surface. It is employed in the optic ...
+
BTDF, a 4+1 dimensional function of the scattering distribution from a single
point/
pixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a Raster graphics, raster image, or the smallest addressable element in a dot matrix display device. In most digital display devices, p ...
/
vertex.
Columbia Utrecht Reflectance and Texture DatabaseBTF Database Bonn and Measurement LabCVPR 2010 BTF Modeling TutorialBTFbase - 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
References
{{DEFAULTSORT:Bidirectional Texture Function
3D rendering