Editing Metropolis light transport

{{short description|Application of the Metropolis–Hastings algorithm to image rendering}}
{{More footnotes|date=February 2014}}
'''Metropolis light transport''' ('''MLT''') is a [[global illumination]] application of a [[Monte Carlo method]] called the [[Metropolis–Hastings algorithm]] to the [[rendering equation]] for generating images from detailed physical descriptions of [[3D computer graphics|three-dimensional]] scenes.<ref>{{Cite book | last1 = Veach | first1 = E. | last2 = Guibas | first2 = L. J. | doi = 10.1145/258734.258775 | chapter = Metropolis light transport | title = Proceedings of the 24th annual conference on Computer graphics and interactive techniques - SIGGRAPH '97 | page = 65 | year = 1997 | isbn = 978-0-89791-896-1 | citeseerx = 10.1.1.40.2090 | s2cid = 1832504 }}</ref><ref>{{cite web|author1=Eric Veach|author2-link=Leonidas J. Guibas|author2=Leonidas J. Guibas|title=Metropolis Light Transport|url=http://graphics.stanford.edu/papers/metro/metro.pdf|publisher=[[Stanford University]]|author1-link=Eric Veach}}</ref>

The procedure constructs paths from the eye to a light source using [[path tracing#Bidirectional path tracing|bidirectional path tracing]], then constructs slight modifications to the path.  Some careful statistical calculation (the Metropolis algorithm) is used to compute the appropriate distribution of brightness over the image.  This procedure has the advantage, relative to bidirectional path tracing, that once a path has been found from light to eye, the algorithm can then explore nearby paths; thus difficult-to-find light paths can be explored more thoroughly with the same number of simulated photons.  In short, the algorithm generates a path and stores the path's 'nodes' in a list. It can then modify the path by adding extra nodes and creating a new light path. While creating this new path, the algorithm decides how many new 'nodes' to add and whether or not these new nodes will actually create a new path.

Metropolis light transport is an unbiased method that, in some cases (but not always), converges to a solution of the rendering equation faster than other unbiased algorithms such as path tracing or bidirectional path tracing.{{Citation needed|date=July 2010}}

Energy Redistribution Path Tracing (ERPT) uses Metropolis sampling-like mutation strategies instead of an intermediate [[probability distribution]] step.<ref name="erpt">{{cite CiteSeerX |title=Energy Redistribution Path Tracing |author1=David Cline |author2=Justin Talbot |author3=Parris Egbert |citeseerx=10.1.1.63.5938}}</ref>

==See also==
* [[Nicholas Metropolis]]  &ndash; The physicist after whom the algorithm is named
''Renderers using MLT:''
* [[Arion (software)|Arion]] &ndash; A commercial unbiased renderer based on path tracing and providing an MLT sampler
* [[Nvidia Iray]] ([http://www.nvidia-arc.com/iray.html external link]) &ndash; An unbiased renderer that has an option for MLT<ref>{{cite web|url=http://www.nvidia-arc.com/products/iray/features.html |title=NVIDIA Advanced Rendering: NVIDIA Iray |publisher=Nvidia-arc.com |access-date=2014-02-03}}</ref><ref>{{cite web|url=http://blog.irayrender.com/post/51722647664/the-architectural-and-caustic-samplers |title=The Architectural and Caustic samplers - iray dev blog |publisher=Blog.irayrender.com |date=2013-05-30 |access-date=2014-02-03}}</ref><ref>{{cite arXiv |eprint= 1705.01263 |title=The Iray Light Transport Simulation and Rendering System |last1= Keller |first1=Alexander |last2=Wächter |first2=Carsten |last3=Raab |first3=Matthias |last4=Seibert |first4=Daniel |author5=Dietger van Antwerpen |last6=Korndörfer |first6=Johann |last7=Kettner |first7=Lutz |class=cs.GR |date=2017 }}</ref>
* [[Kerkythea]] &ndash; A free unbiased 3D renderer that uses MLT
* [[LuxCoreRender]] &ndash; An open source unbiased renderer that uses MLT
* [[Mitsuba Renderer]] ([http://www.mitsuba-renderer.org web site])  A research-oriented renderer which implements several MLT variants
* [[Octane Render]] &ndash; A commercial unbiased renderer that uses MLT
* [[Indigo Renderer]] ([https://www.indigorenderer.com web site]) &ndash; An unbiased, photorealistic GPU and CPU renderer that supports MLT and is aimed at ultimate image quality, by accurately simulating the physics of light.

==References==
{{Reflist}}

==External links==
* [http://graphics.stanford.edu/papers/metro/ Metropolis project at Stanford]
* [http://www.mitsuba-renderer.org Homepage of the Mitsuba renderer]
* [http://www.luxrender.net/ LuxRender - an open source render engine that supports MLT]
* [http://www.kerkythea.net/ Kerkythea 2008 - a freeware rendering system that uses MLT]
* [https://web.archive.org/web/20061202194353/http://rivit.cs.byu.edu/a3dg/publications/metropolisTutorial.pdf A Practical Introduction to Metropolis Light Transport]
* [http://repository.tudelft.nl/view/ir/uuid%3A4a5be464-dc52-4bd0-9ede-faefdaff8be6/ Unbiased physically based rendering on the GPU]

[[Category:Monte Carlo methods]]
[[Category:Global illumination algorithms]]


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