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==Overview of the BxDF functions==
[[Image:BSSDF01 400.svg|thumb|right|250px|BRDF vs. BSSRDF]]
* '''BRDF''' ('''[[Bidirectional reflectance distribution function]]''')<ref name="nicodemus1977">{{cite web|last1=Nicodemus|first1=F. E.|last2=Richmond|first2=J. C.|last3=Hsia|first3=J. J.|last4=Ginsberg|first4=I. W.|last5=Limperis|first5=T.|year=1977|title=Geometrical Considerations and Nomenclature for Reflectance|url=http://graphics.stanford.edu/courses/cs448-05-winter/papers/nicodemus-brdf-nist.pdf|publisher=Technical Report NBS MN-160, National Bureau of Standards|accessdate=14 July 2014}}▼
*'''BDF''' ('''Bidirectional distribution function''') is collectively defined by BRDF and BTDF.▼
▲*'''BRDF''' ('''[[Bidirectional reflectance distribution function]]''')<ref name="nicodemus1977">{{cite web|last1=Nicodemus|first1=F. E.|last2=Richmond|first2=J. C.|last3=Hsia|first3=J. J.|last4=Ginsberg|first4=I. W.|last5=Limperis|first5=T.|year=1977|title=Geometrical Considerations and Nomenclature for Reflectance|url=http://graphics.stanford.edu/courses/cs448-05-winter/papers/nicodemus-brdf-nist.pdf|publisher=Technical Report NBS MN-160, National Bureau of Standards|accessdate=14 July 2014}}
</ref> is a simplified BSSRDF, assuming that light enters and leaves at the same point (''see the image on the right'').
* '''BTDF''' ('''Bidirectional transmittance distribution function''')<ref name="bartell1980"/> is similar to BRDF but for the opposite side of the surface. (''see the top image'').
▲* '''BDF''' ('''Bidirectional distribution function''') is collectively defined by BRDF and BTDF.
* '''BSSRDF''' ('''Bidirectional scattering-surface reflectance distribution function''' or '''Bidirectional surface scattering RDF''')<ref name="nicodemus1977" /><ref name="jensen2001">{{cite book|last1=Jensen|first1=H. W.|url=https://archive.org/details/siggraph2001conf00fium/page/511|title=Proceedings of the 28th annual conference on Computer graphics and interactive techniques - SIGGRAPH '01|last2=Marschner|first2=S. R.|last3=Levoy|first3=M.|last4=Hanrahan|first4=P.|website=graphics.ucsd.edu/~henrik/papers/bssrdf/|publisher=Proceedings of ACM SIGGRAPH 2001|year=2001|isbn=978-1581133745|pages=[https://archive.org/details/siggraph2001conf00fium/page/511 511–518]|chapter=A Practical Model for Subsurface Light Transport|citeseerx=10.1.1.503.7787|doi=10.1145/383259.383319|chapter-url=http://jbit.net/~sparky/bssrdf.pdf|accessdate=14 July 2014}}</ref> describes the relation between outgoing radiance and the incident flux, including the phenomena like [[subsurface scattering]] (SSS). The BSSRDF describes how light is transported between any two rays that hit a surface.
* '''BSSTDF''' ('''Bidirectional scattering-surface transmittance distribution function''') is like BTDF but with subsurface scattering.
* '''BSSDF''' ('''Bidirectional scattering-surface distribution function''') is collectively defined by BSSTDF and BSSRDF. Also known as '''BSDF''' ('''Bidirectional scattering distribution function''').
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