Optical flow: Difference between revisions

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'''Optical flow''' or '''optic flow''' is the pattern of apparent [[motion (physics)|motion]] of objects, surfaces, and edges in a visual scene caused by the [[relative motion]] between an observer and a scene.<ref>{{Cite book |url={{google books|plainurl=yes|id=CSgOAAAAQAAJ|pg=PA77|text=optical flow}} |title=Thinking in Perspective: Critical Essays in the Study of Thought Processes |last1=Burton |first1=Andrew |last2=Radford |first2=John |publisher=Routledge |year=1978 |isbn=978-0-416-85840-2}}</ref><ref>{{Cite book |url={{google books|plainurl=yes|id=-I_Hazgqx8QC|pg=PA414|text=optical flow}} |title=Electronic Spatial Sensing for the Blind: Contributions from Perception |last1=Warren |first1=David H. |last2=Strelow |first2=Edward R. |publisher=Springer |year=1985 |isbn=978-90-247-2689-9}}</ref> Optical flow can also be defined as the distribution of apparent velocities of movement of brightness pattern in an image.<ref>{{Cite journal |last1=Horn |first1=Berthold K.P. |last2=Schunck |first2=Brian G. |date=August 1981 |title=Determining optical flow |url=http://image.diku.dk/imagecanon/material/HornSchunckOptical_Flow.pdf |journal=Artificial Intelligence |language=en |volume=17 |issue=1–3 |pages=185–203 |doi=10.1016/0004-3702(81)90024-2|hdl=1721.1/6337 }}</ref>

The concept of optical flow was introduced by the American psychologist [[James J. Gibson]] in the 1940s to describe the visual stimulus provided to animals moving through the world.<ref>{{Cite book |title=The Perception of the Visual World |last=Gibson |first=J.J. |publisher=Houghton Mifflin |year=1950}}</ref> Gibson stressed the importance of optic flow for [[Affordance|affordance perception]], the ability to discern possibilities for action within the environment. Followers of Gibson and his [[Ecological Psychology|ecological approach to psychology]] have further demonstrated the role of the optical flow stimulus for the perception of movement by the observer in the world; perception of the shape, distance and movement of objects in the world; and the control of [[Animal locomotion|locomotion]].<ref>{{Cite journal |last1=Royden |first1=C. S. |last2=Moore |first2=K. D. |year=2012 |title=Use of speed cues in the detection of moving objects by moving observers |journal=Vision Research |volume=59 |pages=17–24 |doi=10.1016/j.visres.2012.02.006|pmid=22406544 |s2cid=52847487 |doi-access=free }}</ref>

The term optical flow is also used by roboticists, encompassing related techniques from image processing and control of navigation including [[motion detection]], [[Image segmentation|object segmentation]], time-to-contact information, focus of expansion calculations, luminance, [[motion compensation|motion compensated]] encoding, and stereo disparity measurement.<ref name="Kelson R. T. Aires, Andre M. Santana, Adelardo A. D. Medeiros 2008">{{Cite book |url=http://www.dca.ufrn.br/~adelardo/artigos/SAC08.pdf |title=Optical Flow Using Color Information |last1=Aires |first1=Kelson R. T. |last2=Santana |first2=Andre M. |last3=Medeiros |first3=Adelardo A. D. |publisher=ACM New York, NY, USA |year=2008 |isbn=978-1-59593-753-7}}</ref><ref name="S. S. Beauchemin, J. L. Barron 1995">{{Cite journal |url=http://portal.acm.org/ft_gateway.cfm?id=212141&type=pdf&coll=GUIDE&dl=GUIDE&CFID=72158298&CFTOKEN=85078203 |title=The computation of optical flow |last1=Beauchemin |first1=S. S. |last2=Barron |first2=J. L. |journal=ACM Computing Surveys |publisher=ACM New York, USA |year=1995|volume=27 |issue=3 |pages=433–466 |doi=10.1145/212094.212141 |s2cid=1334552 |doi-access=free }}</ref>

== Estimation ==

Optical flow can be estimated in a number of ways. Broadly, optical flow estimation approaches can be divided into machine learning based models (sometimes called data-driven models), classical models (sometimes called knowledge-driven models) which do not use machine learning and hybrid models which use aspects of both learning based models and classical models.<ref name="Zhai_Survey_2021">{{cite journal |last1=Zhai |first1=Mingliang |last2=Xiang |first2=Xuezhi |last3=Lv |first3=Ning |last4=Kong |first4=Xiangdong |title=Optical flow and scene flow estimation: A survey |journal=Pattern Recognition |date=2021 |volume=114 |pages=107861 |doi=10.1016/j.patcog.2021.107861 |url=https://www.sciencedirect.com/science/article/pii/S0031320321000480}}</ref>