Bidirectional scattering distribution function: Difference between revisions

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The definition of the '''BSDF''' ('''bidirectional scattering distribution function''') is not well standardized. The term was probably introduced in 1980 by Bartell, Dereniak, and Wolfe.<ref name=bartell1980>{{cite webjournal

|last1=Bartell

|first1=F. O.

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|first3=W. L.

|title=The theory and measurement of bidirectional reflectance distribution function (BRDF) and bidirectional transmittance distribution function (BTDF)

|volume=0257

|url=http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1230783

|publisher=Proceedings of SPIE Vol. 257 Radiation Scattering in Optical Systems

|accessdate=14 July 2014

|pages=154–160

|doi=10.1117/12.959611

|year=1980}}|series=Radiation Scattering in Optical Systems

}}

</ref> Most often it is used to name the general mathematical function which describes the way in which the light is scattered by a surface. However, in practice this phenomenon is usually split into the reflected and transmitted components, which are then treated separately as '''BRDF''' ('''[[bidirectional reflectance distribution function]]''') and '''BTDF''' ('''bidirectional transmittance distribution function''').

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* The term '''BSDF''' is sometimes used in a slightly different context, for the function describing the amount of the scatter (not scattered light), simply as a function of the incident light angle. An example to illustrate this context: for perfectly lambertian surface the BSDF (angle)=const. This approach is used for instance to verify the output quality by the manufacturers of the glossy surfaces.{{clarify|date=November 2012}}

* Another recent usage of the term '''BSDF''' can be seen in some 3D packages, when vendors use it as a 'smart' category to encompass the simple well known cg algorithms like [[Phong reflection model|Phong]], [[Blinn–Phong reflection model|Blinn–Phong]] etc.

* Acquisition of the BSDF over the [[human face]] in 2000 by [[Paul Debevec|Debevec]] et al.<ref name="Deb2000">{{cite webbook

| last = Debevec

| first = Paul

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| author5 = Westley Sarokin

| author6 = Mark Sagar

| titlechapter = Acquiring the reflectance field of a human face

| workjournal =

| publisherpages = ACM145–156

| publisher = ACM

| year = 2000

| chapter-url = http://dl.acm.org/citation.cfm?id=344855

| chapter-format =

| doi = 10.1145/344779.344855

| accessdate = 2013-07-21| title = Proceedings of the 27th annual conference on Computer graphics and interactive techniques - SIGGRAPH '00

| accessdate = 2013-07-21}}

| isbn = 978-1581132083

</ref> was one of the last key breakthroughs on the way to fully [[virtual cinematography]] with its ultra-photorealistic [[digital look-alike]]s. The team was the first in the world to isolate the [[subsurface scattering]] component (a specialized case of BTDF) using the simplest [[light stage]], consisting on moveable light source, moveable high-res [[digital camera]], 2 [[polarizers]] in a few positions and really simple [[algorithm]]s on a modest [[computer]].<ref name="Deb2000"/> The team utilized the existing scientific knowledge that [[light]] that is reflected and scattered from the air-to-oil layer retains its [[Polarization (waves)|polarization]] while light that travels within the [[skin]] loses its polarization.<ref name="Deb2000"/> The subsurface scattering component can be [[computer simulation|simulated]] as a steady high-scatter glow of light from within the [[3D model|model]]s, without which the skin does not look realistic. [[ESC Entertainment]], a company set up by [[Warner Brothers Pictures]] specially to do the visual effects / virtual cinematography system for [[The Matrix Reloaded]] and [[The Matrix Revolutions]] isolated the parameters for an approximate analytical BRDF which consisted of [[lambertian]] [[diffuse|diffusion]] component and a modified [[specular]] [[phong reflection model|Phong]] component with a [[Fresnel equations|Fresnel]] type of [[Visual effects|effect]].<ref name="HaD2004">{{cite web

}}

</ref> was one of the last key breakthroughs on the way to fully [[virtual cinematography]] with its ultra-photorealistic [[digital look-alike]]s. The team was the first in the world to isolate the [[subsurface scattering]] component (a specialized case of BTDF) using the simplest [[light stage]], consisting on moveable light source, moveable high-res [[digital camera]], 2 [[polarizers]] in a few positions and really simple [[algorithm]]s on a modest [[computer]].<ref name="Deb2000"/> The team utilized the existing scientific knowledge that [[light]] that is reflected and scattered from the air-to-oil layer retains its [[Polarization (waves)|polarization]] while light that travels within the [[skin]] loses its polarization.<ref name="Deb2000"/> The subsurface scattering component can be [[computer simulation|simulated]] as a steady high-scatter glow of light from within the [[3D model|model]]s, without which the skin does not look realistic. [[ESC Entertainment]], a company set up by [[Warner Brothers Pictures]] specially to do the visual effects / virtual cinematography system for [[The Matrix Reloaded]] and [[The Matrix Revolutions]] isolated the parameters for an approximate analytical BRDF which consisted of [[lambertian]] [[diffuse|diffusion]] component and a modified [[specular]] [[phong reflection model|Phong]] component with a [[Fresnel equations|Fresnel]] type of [[Visual effects|effect]].<ref name="HaD2004">{{cite webbook

| last = Haber

| first = Jörg

| authorlink =

| author2 = Demetri Terzopoulos

| titlechapter = Facial modeling and animation

| workjournal =

| publisherpages = ACM6–es

| publisher = ACM

| year = 2004

| chapter-url = http://dl.acm.org/citation.cfm?id=1103906

| chapter-format = .

| doi = 10.1145/1103900.1103906

| accessdate = 2013-08-19}}</ref>| title = Proceedings of the conference on SIGGRAPH 2004 course notes - GRAPH '04

| isbn = 978-0111456781

}}</ref>

==Overview of the BxDF functions==

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|accessdate=14 July 2014

|year=1977}}

</ref><ref name="jensen2001">{{cite webbook|chapter-url=http://jbit.net/~sparky/bssrdf.pdf|titlechapter=A Practical Model for Subsurface Light Transport|last2=Marschner|first2=S. R.|date=|year=2001|website=graphics.ucsd.edu/~henrik/papers/bssrdf/|publisher=Proceedings of ACM SIGGRAPH 2001|pages=511–518|doi=10.1145/383259.383319|archive-url=|archive-date=|dead-url=|last3=Levoy|first3=M.|last4=Hanrahan|first4=P.|last1=Jensen|first1=H. W.|title=Proceedings of the 28th annual conference on Computer graphics and interactive techniques - SIGGRAPH '01|accessdate=14 July 2014|isbn=978-1581133745|citeseerx=10.1.1.503.7787}}</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.

*'''BRDF''' ('''[[Bidirectional reflectance distribution function]]''')<ref name="nicodemus1977"/> 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'').