An MPEG-Processor-based Robot Vision System for Real-Time De(4)

This paper describes a PC-based vision system that can be used to detect moving objects from a mobile robot. An image processing board equipped with an MPEG motion estimation processor calculates a sparse but robust optic flow in real-time. An algorithm to

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parisonofa)theestimatedandb)thecorrespondingodometricvalue

Takingintoaccountonlythevectorsof,theestimate

forthecamerarotationcanagainbecalculatedaccordingtoEqn.7.Fig.6demonstratestheperformanceoftheback-grounddetectionstatisticallyusingtypicalimagesequencescontainingonetoseveralmovingobjects.Inthisexperi-ment,thecameraisnotmoving,i.e.theestimatedshouldbe.Eachdotcorrespondstoone ow eld.Theab-scissadepictsthepercentageof owvectorsbelongingtothebackground,theordinatetheestimated(herein

Simplyusingthelast

tocalculateabiasvector

transformsthelimitationoftherotationalvelocitytoa

limitationoftherotationalacceleration.Thus,agoodesti-mateisessentialfortheoveralloperationofthevisionsystem.

3.2Segmentationofmovingobjects

Inthecaseofoneormoremovingobjectsintheobservedscenethedeterminationoftherotationhastobemodi ed.

ofvectorsbelongingtoamovingobjectnolongerThe

ofthecamera.Segmentationcanbecoincidewiththe

performedbyclusteringvectorsaccordingtotheir.Asimpleclusteralgorithmhasproventobesuf cientinthe

,experiments.Vectorsaresortedbyincreasingvaluesof

so

Thentheyarecombinedtoformasetofclusters

aslongastheysatisfythecriterion.Therefore

.

clustersbuildthe rsthypothesesfortheseg-These

mentationoftheoptic ow.Unfortunately,noteachclustercorrespondstoonemovingobject,becausetheassumptionsthatledtoEqn.4areonlytrueforarestrictedcameramo-tion,i.e.forthevectorsbelongingtothebackground.Sointhisstep,onlyaclassi cationbackgroundversusnotback-groundcanbemadeforeachcluster.Goodresultscanbeachievedbydeclaringtheclusterasbackgroundthatcontainsthesetofvectorswiththelargestspatialvariance.Thisapproachisinspiredbytheobservationthattheback-groundistheonly”object”notcorrespondingtoacompactimageregion.

Since,asintheliveexperimentsonlythe rst eldofeachframeisused,thevarianceindirectionismuchmoremeaningfulthanindirectionandcanbeusedexclu-sively: