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

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

AnMPEG-Processor-basedRobotVisionSystemforReal-TimeDetectionof

MovingObjectsbyaMovingObserver

NorbertO.St¨of erandZoltanSchnepf

LaboratoryforProcessControlandReal-TimeSystems

TechnischeUniversit¨atM¨unchenD-80333M¨unchen,Germany

stof er@lpr.ei.tum.de,www.lpr.ei.tum.de/stof er/

Abstract

ThispaperdescribesaPC-basedvisionsystemthatcanbeusedtodetectmovingobjectsfromamobilerobot.AnimageprocessingboardequippedwithanMPEGmotiones-timationprocessorcalculatesasparsebutrobustoptic owinreal-time.Analgorithmtoevaluatethiskindofoptic owhasbeenrealizedinsoftware.Itdeterminesrelevantmotionparametersandasimplesceneinterpretationintermsofmovingobjectregions.Theimageprocessingboardandthealgorithmarepresentedinsomedetail;theperformanceofthesystemisdemonstratedbyexperiments.

1.

Introduction

Usingourexperimen-talrobotMARVIN(MobileAutonomousRobotwithVIsion-basedNavigation,seeFig.1),wearecurrentlyworkingontheautono-mousexplorationofof ce-typeenvironments.Primar-ilyvisionisusedtobuild3Dworldmodels[2].Im-portantcuestotheinterpre-tationofanobservedscenecanbeobtainedbytheeval-uationofmotion.Movingobjects(typicallypeopleintheabove-mentionedenvi-ronment)havetobedistin-Figure1.MARVINguishedfromstaticpartsof

thesceneontheonehandandhavetobetakenintoaccountfordynamicmotionplanningontheotherhand.Thisdetec-tionofmovingobjectshastotakeplaceduringthemotion

oftherobotitself.

Three-dimensionalmotionisprojectedontoatwo-dimensionalvelocity eld(ordisplacement eldinthecaseofisochronoussampling)ontheimageplaneofthecamera.Thisvector eldiscommonlytermedoptic ow(ormorepreciselyimage ow).Ifthedisplacementvectorsareregardedtobeequivalenttothevelocityvectors(anac-ceptableassumptionforrealisticframeratesandvelocities[1])andthefocallengthofthecameraisnormalizedto1(amathematicalconveniencethatdoesnotrestrictgenerality),theoptic ow

canbecalculatedaccordingtothefollowing: