# Bidirectional texture function

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'''Bidirectional texture function''' (BTF) <ref name="r3" /><ref name="r4" /><ref name="r1" /> is a 6-[dimension](/source/dimension)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 <ref name="r3" /><ref name="r4" /> and similar terms have since been introduced including [BSSRDF](/source/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](/source/photorealistic) material rendering of objects in [virtual reality](/source/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](/source/Bidirectional_scattering_distribution_function) == [BRDF](/source/Bidirectional_reflectance_distribution_function) + [BTDF](/source/Bidirectional_transmittance_distribution_function), a 4+1 dimensional function of the scattering distribution from a single [point](/source/point_(geometry))/[pixel](/source/pixel)/[vertex](/source/Vertex_(computer_graphics)).
*[https://www.cs.columbia.edu/CAVE/software/curet/ Columbia Utrecht Reflectance and Texture Database] 
*[http://cg.cs.uni-bonn.de/en/projects/btfdbb/ BTF Database Bonn and Measurement Lab]
*[http://ro.utia.cas.cz/10cvpr_tutorial/ CVPR 2010 BTF Modeling Tutorial]
*[http://www.cgg.cvut.cz/members/havravla/btfbase/ BTFbase - BTF compression based on a multi-level vector quantization (free BTF shader)]
*[http://btf.utia.cas.cz/ UTIA BTF Database - a new source of publicly available bidirectional texture function measurements]

==References==
{{Reflist|refs=
<ref name="r1">{{cite journal |doi=10.1109/TPAMI.2008.246 |title=Bidirectional Texture Function Modeling: A State of the Art Survey |author=Jiří Filip |author2=Michal Haindl |year=2009 |journal=IEEE Transactions on Pattern Analysis and Machine Intelligence |volume=31 |issue=11 |pages=1921–1940 |pmid=19762922 |s2cid=9283615 |citeseerx=10.1.1.494.2660 }}</ref>
<ref name="r2">{{cite journal |url=http://www3.interscience.wiley.com/journal/123233573/abstract
 |archive-url=https://web.archive.org/web/20100804074727/http://www3.interscience.wiley.com/journal/123233573/abstract
 |url-status=dead
 |archive-date=2010-08-04
 |title=Bidirectional Texture Function Compression based on Multi-Level Vector Quantization |author=Vlastimil Havran |author2=Jiří Filip |author3=Karol Myszkowski  |year=2009 |journal=Computer Graphics Forum |volume=29 |issue=1  |pages=175–190 }}</ref>
<ref name="r3">{{cite journal |url=http://www.ece.rutgers.edu/~kdana
|title=Reflectance and texture of real world surfaces | author=Kristin J. Dana|author2=Bram van Ginneken |author3=Shree K. Nayar |author4=Jan J. Koenderink | year = 1999| journal= ACM Transactions on Graphics|volume=18 |issue=1| pages=1–34|doi=10.1145/300776.300778 |s2cid=622815 |doi-access=free }}</ref>
<ref name="r4">{{cite web |title=Reflectance and texture of real world surfaces | author=Kristin J. Dana|author2=Bram van Ginneken |author3=Shree K. Nayar |author4=Jan J. Koenderink | year = 1996| work = Columbia University Technical Report CUCS-048-96}}</ref>
<ref name="r5">{{cite web 
|title=A practical model for subsurface light transport | author=Jensen, H.W.|author2=Marschner, S.R.|author3=Levoy, M.|author4=Hanrahan, P.| year = 2001| work = ACM SIGGRAPH | pages=511–518 }}</ref>
<ref name="r6">{{cite journal |title=Skin Texture Modeling | author=Oana G. Cula |author2=Kristin J. Dana |author3=Frank P. Murphy |author4=Babar K. Rao| year = 2005| journal= International Journal of Computer Vision  | pages=97–119 }}</ref>
<ref name="r7">{{cite book |url=https://www.springer.com/computer/image+processing/book/978-1-4471-4901-9 |title=Visual Texture: Accurate Material Appearance Measurement, Representation and Modeling
 |author1=Michal Haindl |author2=Jiří Filip |year=2013 |series= Advances in Computer Vision and Pattern Recognition |publisher=Springer-Verlag London 2013 |isbn=978-1-4471-4901-9 |pages=285 }}</ref>
}}

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Category:3D rendering

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Adapted from the Wikipedia article [Bidirectional texture function](https://en.wikipedia.org/wiki/Bidirectional_texture_function) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Bidirectional_texture_function?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.