Chapter 6 - Feature Extraction

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1、§6-FeatureExtractionDr.DirkSchniedersDepartmentofComputerScienceTheUniversityofHongKongLevelsofProcesses★Typically,threetypesofprocessescanbeclassifiedinthiscontinuum:★low-levelprocesses,★mid-levelprocesses,and★high-levelprocessesImageComputerProcessi

2、ngVisionlow-levelmid-levelhigh-levelprocessesprocessesprocesses2013-2014COMP75022Mid-LevelProcesses★Mid-levelprocesses★Higherleveltaskse.g.imagesegmentation,imagedescription,classificationandrecognition★Inputsaregenerallyimages★Outputsareattributesext

3、ractedfromtheimagese.g.edges,contours,identityoftheindividualobjectsmid-levelimageprocessattributes2013-2014COMP75023ImageInterpretation★Theintensityvalueofeachpixeldependsonanumberoffactors(1)Thenatureanddistributionoflightsources(2)Theshapeofthestru

4、cturesinthescene(3)Thereflectancepropertiesofthesurfaces(4)Thepositionofthecamera(5)Thepropertiesofthelensandtheimagesensor★Typically,computervisionapplicationsaimatdeducingthestructuresinthescene(2)andthepositionandpropertiesofthecamera(4,5)fromtheim

5、ageindependentoftheothers2013-2014COMP75024WhyFeatureExtraction?★Eachimagecontainsahugeamountofdata★E.g.,1920*1080*8bits★Theaimoffeatureextractionistodramaticallyreducetheamountofdataby★preservingtheusefulinformationintheimages(e.g.,thoserelatedtocame

6、raposeandscenestructures)★discardingtheredundantinformationintheimages(e.g.,thoserelatedtoreflectanceandlightingconditions)★Allsubsequentinterpretationisthenperformedonthegenericrepresentation,nottheoriginalimage2013-2014COMP75025SalientFeatures★Edgea

7、ndcornerfeaturesarecommonlyusedincomputervision★Theyarefairlycheaptocompute★Theyrequirerelativelysmallstoragespace★Theyaresomewhatinvarianttochangesinlighting★Theyprovidestrongcluesthatcanhelpthevisionprocess2013-2014COMP75026ImageStructure1.2.3.2013-

8、2014COMP75027ImageStructure-Featureless1.Afeaturelessregionischaracterizedbyasmoothvariationofintensities2013-2014COMP75028ImageStructure-Edge2.Apatchcontaininganedgerevealsanintensitydiscontinuityinonedirection2013-2014COMP75029ImageStructure