07 A state of the art in structured light patterns

AstateoftheartinstructuredlightpatternsforsurfaceprofilometryJoaquimSalvia,,SergioFernandeza,,TomislavPribanicb,XavierLladoaaInstituteofInformaticsandApplications,UniversityofGirona,Av.LluisSantaloS/N,E-17071Girona,SpainbFacultyofElectricalEngineeringandComputing,UniversityofZagreb,Unska3,HR-10000Zagreb,CroatiaarticleinfoArticlehistory:Received21July2009Receivedinrevisedform16November2009Accepted5March2010Keywords:CodedpatternsPatternprojectionStructuredlightFouriertransformprofilometry3DmeasuringdevicesActivestereoComputervisionabstractShapereconstructionusingcodedstructuredlightisconsideredoneofthemostreliabletechniquestorecoverobjectsurfaces.Havingacalibratedprojector–camerapair,alightpatternisprojectedontothesceneandimagedbythecamera.Correspondencesbetweenprojectedandrecoveredpatternsarefoundandusedtoextract3Dsurfaceinformation.Thispaperpresentsanup-to-datereviewandanewclassificationoftheexistingtechniques.Someofthesetechniqueshavebeenimplementedandcompared,obtainingbothqualitativeandquantitativeresults.Theadvantagesanddrawbacksofthedifferentpatternsandtheirpotentialsarediscussed.&2010ElsevierLtd.Allrightsreserved.1.IntroductionThree-dimensionalmeasurementconstitutesanimportanttopicincomputervision,havingdifferentapplicationssuchasrangesensoring,industrialinspectionofmanufacturedparts,reverseengineering(digitizationofcomplex,free-formsurfaces),objectrecognition,3Dmapbuilding,biometrics,clothingdesignandothers.Thedevelopedsolutionsaretraditionallycategorizedintocontactandnon-contacttechniques.Contactmeasurementtechniqueshavebeenusedforalongtimeinreverseengineeringandindustrialinspections.Themainproblemsofcontacttechniquesaretheirslowperformanceandthehighcostofusingmechanicallycalibratedpassivearms[1].Besides,thefactoftouchingtheobjectisnotfeasibleformanyapplications.Non-contacttechniquesweredevelopedtocopewiththeseproblems,andhavebeenwidelystudied.Non-contacttechniquescanbeclassifiedintotwodifferentcategories:activeandpassive.Inpassiveapproaches,thesceneisfirstimagedbyvideocamerasfromtwoormorepointsofviewandcorrespondencesbetweentheimagesarefound.Itisimportanttomentionthatthecamerashavetobepreviouslycalibrated[2].Themainproblemexperimentedwhenusingthisapproachisasparsereconstruc-tionsincedensityisdirectlyrelatedtothetextureoftheobject.Thiscomplicatestheprocessoffindingcorrespondencesinthepresenceoftexturelesssurfaces[3].Therefore,passiverecon-structionisratherlimitedtoreconstructdense3Dsurfaces,duetotheproblemoffindingcorrespondences[4].Methodsbasedonstructuredlight(activetechniques)cametocopewiththisissue,creatingcorrespondencesandgivingspecificcode-wordstoeveryunitarypositionintheimage.Inthisapproachoneofthecamerasissubstitutedbyanactivedevice(aprojector),whichprojectsastructuredlightpatternontothescene.Thisactivedeviceismodeledasaninversecamera,beingthecalibrationstepasimilarproceduretotheoneusedinaclassicalstereo-visionsystem[5].Theprojectedpatternimposestheillusionoftextureontoanobject,increasingthenumberofcorrespondences[6].Therefore,surfacereconstructionispossiblewhenlookingfordifferencesbetweenprojectedandrecordedpatterns.Inthispaper,anexhaustiveanalysisofthedifferentcodingstrategiesusedinactivestructuredlightisdone,focusingontheadvancementspresentedinthelastyears.Anewclassificationregardingthestrategyusedtocreatethepatternisproposed,comparingsomecommoncharacteristicsbetweenthem.Feasi-bilityandaccuracyareanalysed,givingbothqualitativeandquantitativeresultsfortheimplementedtechniques.Thispaperisstructuredasfollows:Section2presentsaclassificationofthedifferenttechniques.DiscretepatternbasedcodificationisstudiedinSection3,whileSection4dealswiththecontinuousones.TheresultsofimplementingsomeofthemostrelevanttechniquesareshowedinSection5,comparingtheirprosandcons.Finally,Section6concludeswithadiscussionoftheARTICLEINPRESSContentslistsavailableatScienceDirectjournalhomepage::10.1016/j.patcog.2010.03.004PrincipalCorrespondingauthor.Tel.:[phone];fax:[phone].Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddresses:[e-mail](J.Salvi),[e-mail](S.Fernandez),[e-mail](T.Pribanic),[e-mail](X.Llado).PatternRecognition43(2010)2666–2680ARTICLEINPRESSsurveyedmethods,pointingoutadvantagesanddisadvantagesofthemostrelevantones.2.ClassificationCodedstructuredlight(CSL)systemsarebasedontheprojectionofonepatternorasequenceofpatternsthatunivocallydeterminethecodewordofapixelwithinanon-periodicregion.CSLhasproducedmanyworksduringthelastdecadesandsomerecopilatoryworkscanbefoundintheliterature.ThisisthecaseofthesurveyspresentedbyBatlleetal.[4]andSalvietal.[7]thatanalysedthedifferentcodedstructuredlighttechniquesexistingintemporalandspatialmultiplexingdomainsuntil1998and2004,respectively.Regardingfrequencymultiplexing,Su[8]reviewedtheFourierTransformProfilometry(FTP)techniquesproposeduntil2001.However,thereisnotanypreviousworkcomparingthethreeapproachestogeth