# Polynomial texture mapping

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{{Short description|Digital imaging technique}}
{{Wiktionary hatnote|redirect=Relighting||relight}}
'''Polynomial [texture mapping](/source/texture_mapping)''' ('''PTM'''), also known as '''Reflectance Transformation Imaging''' (RTI), is a technique of [imaging](/source/digital_imaging) and [interactively](/source/interactive_media) displaying objects under varying [lighting](/source/lighting) conditions to reveal surface phenomena. The data acquisition method is [single camera multi light](/source/Single_camera_multi_light_imaging) (SCML).<ref>{{cite book | doi=10.1117/12.2555685 | chapter=Pixel+: Integrating and standardizing of various interactive pixel-based imagery | title=Optics, Photonics and Digital Technologies for Imaging Applications VI | year=2020 | last1=Vanweddingen | first1=Vincent | last2=Hameeuw | first2=Hendrik | last3=Vandermeulen | first3=Bruno | last4=Vastenhoud | first4=Chris | last5=Watteeuw | first5=Lieve | last6=Lemmers | first6=Frédéric | last7=Van Der Perre | first7=Athena | last8=Konijn | first8=Paul | last9=Van Gool | first9=Luc | last10=Proesmans | first10=Marc |series=Proceedings of SPIE |volume=11353 | page=15 | isbn=9781510634787 | s2cid=216318287 | url=https://lirias.kuleuven.be/handle/123456789/654516 | editor-first1=Peter | editor-first2=Tomasz | editor-last1=Schelkens | editor-last2=Kozacki }}</ref>

==Origins==
The method was originally developed by Tom Malzbender of [HP Labs](/source/HP_Labs) in order to generate enhanced [3D computer graphics](/source/3D_computer_graphics) and it has since been adopted for [cultural heritage](/source/cultural_heritage) applications.<ref name="Economist">{{cite news |url=https://www.economist.com/science-and-technology/2010/03/25/shining-a-light-on-the-past |title=Archaeology and polynomial texture mapping |newspaper=[The Economist](/source/The_Economist) |date=25 March 2010 |accessdate=8 March 2011}}</ref>

==Methodology==
A series of images is captured in a darkened environment with the [camera](/source/camera) in a fixed position and the object lit from different angles (Single Camera Multi Light). Interactive software processes and combines the set of images to enable the user inspecting the object to control a [virtual](/source/virtual_artifact) light source.<ref name="Economist"/> The virtual light source may be manipulated to simulate light from different [angle](/source/angle)s and of different [intensity](/source/irradiance) or [wavelength](/source/wavelength)s to illuminate the surface of artefacts and reveal details.<ref name="Economist"/><ref name="ACRG">{{cite web |url=http://www.southampton.ac.uk/archaeology/acrg/acrg_research_PTM.html |title=Polynomial texture mapping |publisher=[University of Southampton](/source/University_of_Southampton) |accessdate=8 March 2011}}</ref> Open-source tools for processing the captured images and publishing the resulting relightable images on the web are freely available.<ref>{{cite web |url=http://vcg.isti.cnr.it/rti/index.php |title=Reflectance Transformation Imaging (RTI) Tools |publisher= Visual Computing Lab - [ISTI](/source/ISTI) - [CNR](/source/National_Research_Council_(Italy))}}</ref>

==Applications==
Polynomial texture mapping may be used for detailed recording and documentation, [3D modeling](/source/3D_modeling), [edge detection](/source/edge_detection), and to aid the study of [inscriptions](/source/Epigraphy), [rock art](/source/rock_art)<ref>{{cite journal | url=https://www.academia.edu/39963512 | title=First application of Reflectance Transformation Imaging (RTI) on Prehistoric Rock Engravings of the Monte Bego Region (Tende, Alpes-Maritimes, France) |issue=84 |pages=24–30 | journal=International Newsletter on Rock Art | date=January 2019 | last1=Mourey | first1=Jules Masson }}</ref> and other artefacts.<ref name="ACRG"/><ref>{{cite web |url=http://www.southampton.ac.uk/archaeology/acrg/acrg_research_herculaneum_PTM.html |title=Polynomial texture mapping |publisher=[University of Southampton](/source/University_of_Southampton) |accessdate=8 March 2011}}</ref> It has been applied to hundreds of the [Vindolanda tablets](/source/Vindolanda_tablets) by the [Centre for the Study of Ancient Documents](/source/Centre_for_the_Study_of_Ancient_Documents) at the [University of Oxford](/source/University_of_Oxford) in conjunction with the [British Museum](/source/British_Museum).<ref>{{cite journal |url=https://eprints.soton.ac.uk/156253/ |journal=Journal of Archaeological Science |title=Archaeological applications of polynomial texture mapping: analysis, conservation and representation |year=2010 |pages=1–11 |author=Earl, Graeme (''et al.'') |accessdate=8 March 2011|doi=10.1016/j.jas.2010.03.009 |volume=37|issue=8|bibcode=2010JArSc..37.2040E }}</ref> It has also been deployed, by Ben Altshuler of the [Institute for Digital Archaeology](/source/Institute_for_Digital_Archaeology), to scan the [Philae obelisk](/source/Philae_obelisk) at [Kingston Lacy](/source/Kingston_Lacy) and the [Parian Chronicle](/source/Parian_Chronicle) at the [Ashmolean Museum](/source/Ashmolean_Museum); in both cases scans revealed significant, previously illegible text.<ref name=IDA>{{cite web|title=The Parian Marble at The Ashmolean Museum|url=http://digitalarchaeology.org.uk/projects |publisher=Institute for Digital Archaeology |accessdate=24 September 2015}}</ref><ref>{{cite journal |last1=Altshuler |first1=Ben F S |last2=Mannack |first2=Thomas |title=Shedding New Light on Ancient Objects |journal=Arion: A Journal of Humanities and the Classics|date=2014 |volume=22 |issue=1 |pages=53–74 |doi=10.2307/arion.22.1.0053 |jstor=arion.22.1.0053|s2cid=171785310 }}</ref><ref>{{cite web |title=The Digital Marmor Parium Project at the University of Leipzig |url=http://www.digitalmarmorparium.org/}}</ref> Method was also used for identifying microscopic worked antler from [Star Carr](/source/Star_Carr) and recording ancient rock art in [Armenia](/source/Armenia).<ref>{{Cite journal |last=Kennedy |first=Hannah |title=Visual interpretation, survey and graphics: adding value to archaeology |url=https://www.archaeologists.net/sites/default/files/Yearbook%20articles%202020.pdf |journal=2020: Yearbook and Directory |pages=17 |via=Chartered Institute for Archaeologists}}</ref>

A 'dome' supporting twenty-four lights has been used to image paintings in the [National Gallery](/source/National_Gallery) and produce polynomial texture maps, providing information on condition phenomena for [conservation](/source/conservation_and_restoration_of_cultural_heritage) purposes.<ref>{{cite book |title=Digital Heritage:Applying Digital Imaging to Cultural Heritage |url=https://archive.org/details/digitalheritagea00macd |url-access=limited |chapter=Digital Imaging for Easel Paintings |pages=[https://archive.org/details/digitalheritagea00macd/page/n548 525] ff |editor=MacDonald, Lindsay |publisher=[Butterworth-Heinemann](/source/Butterworth-Heinemann) |year=2006 |isbn=978-0-7506-6183-6}}</ref> Studies of the technique at the [National Gallery](/source/National_Gallery) and [Tate](/source/Tate) concluded that it is an effective tool for documenting changes in the condition of paintings, more easily repeatable than [raking light](/source/raking_light) photography, and therefore could be used to assess paintings during structural treatment and before and after loan.<ref>{{cite journal |doi=10.5334/jcms.1021201|journal=Journal of Conservation and Museum Studies |title=Imaging Techniques in Conservation |year=2012 |pages=17–29 |author=Payne, Emma Marie |volume=10|issue= 2|url=https://discovery.ucl.ac.uk/id/eprint/1443164/1/56-566-2-PB.pdf|doi-access=free }}</ref> Twelve dome-based systems built by the University of Southampton have been used to capture thousands of cuneiform tablets at various museums.<ref>{{citation |title=Reflectance transformation imaging systems for ancient documentary artefacts |url=https://eprints.soton.ac.uk/204531/ |publisher=British Computer Society |year=2011|pages=147–154 |isbn=9781906124885 }}</ref><ref>{{citation |title=Reflectance Transformation Imaging (RTI) System for Ancient Documentary Artefacts |url=https://eprints.soton.ac.uk/271582/ |year=2010|pages=116–119 |isbn=9783905673760 |last1=Artusi |first1=Alessandro |publisher=Eurographics Assoc. }}</ref><ref>{{cite web |title=Custom Imaging |url=https://custom-imaging.co.uk/}}</ref>

The technique is now also finding uses in the field of [forensic science](/source/forensic_science), for example in imaging footprints, tyre marks, and indented writing.

==See also==
*[Multispectral image](/source/Multispectral_image)

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20190307055738/http://www.hpl.hp.com/research/ptm/ Polynomial texture mapping] ([Hewlett Packard](/source/Hewlett_Packard))
* [http://www.portusproject.org/technology/2008/07/polynomial-texture-mapping-at-portus/ Project applying polynomial texture mapping to an ancient sculpture] ([University of Southampton](/source/University_of_Southampton) - Archaeological Computing Research Group)
* [http://culturalheritageimaging.org/Technologies/RTI/index.html Reflectance Transformation Imaging (RTI)] (RTI overview on the Cultural Heritage Imaging website)
* [https://lichfield.ou.edu/ Sixteen interactive renderings] of Polynomial Texture Mapping (or RTI) of 8th-century illuminated manuscript, revealing difficult to see dry-point writing ([University of Oklahoma](/source/University_of_Oklahoma))
* [https://www.heritage-visualisation.org/ Heritage Visualisation website] with Pixel+ viewer and an integration solution for Single Camera Multi Light datasets

Category:3D imaging
Category:Conservation and restoration of cultural heritage
Category:Digital imaging
Category:Image processing
Category:Texture mapping
Category:Virtual reality

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