Bidirectional texture function (BTF) [1] is a 7-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 thousands color images of material sample taken during different camera and light positions.
To cope with a massive BTF data with high redundancy, many compression method were proposed [1][2].
Its main application is a photorealistic material rendering of objects in virtual reality systems.