VisionforGraphics视觉图形

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1、TodayFeatureTrackingGoodfeaturestotrack(ShiandTomasipaper)TrackingStructurefromMotionTomasiandKanadeSingularvaluedecompositionExtensionsonMonday(1/29)Multi-viewrelationsThefundamentalmatrixRobustestimationAssignment2outStructurefromMotionReconstructScenegeometryCameramotionUnknowncameraviewpointsSt

2、ructurefromMotionTheSFMProblemReconstructscenegeometryandcameramotionfromtwoormoreimagesTrack2DFeaturesEstimate3DOptimize(BundleAdjust)FitSurfacesSFMPipelineStructurefromMotionStep1:TrackFeaturesDetectgoodfeaturescorners,linesegmentsFindcorrespondencesbetweenframesLucas&Kanade-stylemotionestimation

3、window-basedcorrelationStructurefromMotionStep2:EstimateMotionandStructureSimplifiedprojectionmodel,e.g.,[Tomasi92]2or3viewsatatime[Hartley00]ImagesMotionStructureStructurefromMotionStep3:RefineEstimates“Bundleadjustment”inphotogrammetryDiscussedlastlectureandinTriggsreadingOtheriterativemethodsStr

4、ucturefromMotionStep4:RecoverSurfacesImage-basedtriangulation[Morris00,Baillard99]Silhouettes[Fitzgibbon98]Stereo[Pollefeys99]PoormeshGoodmeshMorrisandKanade,2000FeatureTrackingProblemFindcorrespondencebetweennfeaturesinfimagesIssuesWhat’safeature?Whatdoesitmeanto“correspond”?Howcancorrespondencebe

5、reliablycomputed?TrackingFeaturesApproachComputemotionofasmallimagepatchAlternatively:linesegment,curve,shapeFeatureCorrespondenceCorrespondenceProblemGivenfeaturepatchFinframeJ,findbestmatchinframeISolutionSmalldisplacement:Lukas-KanadeLargedisplacement:discretesearchover(u,v)Choosematchthatminimi

6、zesSSD(ornormalizedcorrelation)Whenwillthisfail?Finddisplacement(u,v)thatminimizesSSDerroroverfeatureregionFeatureDistortionFeaturemaychangeshapeovertimeNeedadistortionmodeltoreallymakethisworkMinimizewithrespecttoWxandWyShiandTomasireadinggivesderivationforaffinemodelFinddisplacement(u,v)thatminim

7、izesSSDerroroverfeatureregionSelectingGoodFeaturesWhat’sa“goodfeature”?SatisfiesbrightnessconstancyHassufficienttexturevariationDoesnothavetoomuchtexturevariationCorrespondstoa“real”surfacepatchDoesnotdefor