局部不变特征.pdf

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1、Outline•Typesoftransformationsandinvariance–ScaleinvarianceLecture13:Localinvariantfeatures•Localfeatures:detectorsanddescriptors–SIFTTuesday,Oct30Prof.KristenGraumanGeometrictransformations•Whatwouldwelikeourimagedescriptionstobeinvariantto?FigurefromT.TuytelaarsECCV2006tutorialPhoto

2、metrictransformationsAndothernuisances…•Noise•Blur•Compressionartifacts•AppearancevariationforacategoryFigurefromT.TuytelaarsECCV2006tutorialClassesoftransformationsExhaustivesearchAmulti-scaleapproach•Euclidean/rigid:Translation+rotation•Similarity:Translation+rotation+uniformscalePr

3、ojectivetransformationSimilaritytransformationTranslationandScalingAffinetransformationTranslation•Affine:Similarity+shear–Validfororthographiccamera,locallyplanarobject•(Projective:Affine+projectivewarps)•Photometric:affineintensitychange–I->aI+bSlidefromT.TuytelaarsECCV2006tutorialE

4、xhaustivesearchExhaustivesearchAmulti-scaleapproachAmulti-scaleapproachSlidefromT.TuytelaarsECCV2006tutorialSlidefromT.TuytelaarsECCV2006tutorialExhaustivesearchKeyideaofinvarianceAmulti-scaleapproachWewanttoextractthepatchesfromeachimageindependently.SlidefromT.TuytelaarsECCV2006tuto

5、rialSlideadaptedfromT.TuytelaarsECCV2006tutorialInvariantlocalfeatures(Good)invariantlocalfeaturesSubsetoflocalfeaturetypes•Reliablydetecteddesignedtobeinvarianttoy1y•Distinctive–Scale2…–Translation•Robusttonoise,blur,etc.y–Rotationd–Affinetransformations•Descriptionnormalizedproperly

6、–Illuminationx1x21)Detectdistinctiveinterestpoints…x2)Extractinvariantdescriptorsd[Mikolajczyk&Schmid,Matasetal.,Tuytelaars&VanGool,Lowe,Kadiretal.,…]Review:cornerdetectionasaninterestInterestpoints:Fromstereotorecognitionoperator•Featuredetectorspreviouslyusedforstereo,motiontracking

7、•Nowalsoforrecognition–Schmid&Mohr1997•Harriscornerstoselectinterestpoints•Rotationallyinvariantdescriptoroflocalimage“flat”region:“edge”:“corner”:regionsnochangeinnochangealongsignificantchange•Identifyconsistentclustersofmatchedfeaturesalldirectionstheedgedirectioninalldirectionstod

8、oreco