visibleinanMRIorSPECTimage. BacktoTop
Point Mapping
TheImageProcessingToolboxsoftwareprovidestoolsto supportpointmappingtodeterminetheparametersofthe transformationrequiredtobringanimageintoalignmentwith anotherimage.Inpointmapping,youpickpointsinapairof imagesthatidentifythesamefeatureorlandmarkinthe images.Then,aspatialmappingisinferredfromthepositions ofthesecontrolpoints. NoteYoumightneedtoperformseveraliterationsof thisprocess,experimentingwithdifferenttypesof transformations,beforeyouachieveasatisfactoryresult .Insomecases,youmightperformsuccessive registrations,removinggrossglobaldistortionsfirst, andthenremovingsmallerlocaldistortionsin subsequentpasses. Thefollowingfigureprovidesagraphicillustrationofthis process.Thisprocessisbestunderstoodbylookingatan example.See Example:RegisteringtoaDigitalOrthophoto foranextendedexample.
Example: Registering to a Digital Orthophoto
Thisexampleillust源自atesthestepsinvolvedinperforming imageregistrationusingpointmapping.Thesestepsinclude: Step1:ReadtheImages Step2:ChooseControlPointsintheImages Step3:SavetheControlPointPairstotheMATLAB Workspace Step4:Fine-TunetheControlPointPairPlacement( Optional) Step5:SpecifytheTypeofTransformationandInferIts Parameters Step6:TransformtheUnregisteredImage Step 1: Read the Images Inthisexample,thebaseimageis ,theMassGISgeoregistered orthophoto.Itisapanchromatic(grayscale)image,supplied bytheMassachusettsGeographicInformationSystem( MassGIS),thathasbeenorthorectifiedtoremovecamera, perspective,andreliefdistortions(viaaspecializedimage transformationprocess).Theorthophotoisalsogeoregistered (andgeocoded)—thecolumnsandrowsofthedigital orthophotoimagearealignedtotheaxesofthe MassachusettsStatePlanecoordinatesystem.Inthe
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Using
in a Script
Ifyouneedtoperformthesamekindofregistrationformany images,youautomatetheprocessbyputtingallthestepsina script.Forexample,youcouldcreateascriptthatlaunchesthe ControlPointSelectionToolwithaninputandabaseimage. Thescriptcouldthenusethecontrolpointsselectedtocreate aTFORMstructureandpasstheTFORMandtheinputimage function,outputtingtheregisteredimage. tothe Todothis,specifythe optionwhenyoucall tolaunchtheControlPointSelectionTool.Withthe

Registering an Image
On this page… Overview PointMapping UsingcpselectinaScript Example:RegisteringtoaDigitalOrthophoto
Overview
Imageregistrationistheprocessofaligningtwoormore imagesofthesamescene.Typically,oneimage,calledthe baseimageorreferenceimage,isconsideredthereferenceto whichtheotherimages,calledinputimages,arecompared. Theobjectofimageregistrationistobringtheinputimage intoalignmentwiththebaseimagebyapplyingaspatial transformationtotheinputimage.Thedifferencesbetween theinputimageandtheoutputimagemighthaveoccurredas aresultofterrainreliefandotherchangesinperspectivewhen imagingthesamescenefromdifferentviewpoints.Lensand otherinternalsensordistortions,ordifferencesbetween sensorsandsensortypes,canalsocausedistortion. Aspatialtransformationmapslocationsinoneimagetonew locationsinanotherimage.(Formoredetails,seeSpatial Transformations)Determiningtheparametersofthespatial transformationneededtobringtheimagesintoalignmentis keytotheimageregistrationprocess. Imageregistrationisoftenusedasapreliminarystepinother imageprocessingapplications.Forexample,youcanuse imageregistrationtoalignsatelliteimagesoftheearth's surfaceorimagescreatedbydifferentmedicaldiagnostic modalities(MRIandSPECT).Afterregistration,youcan comparefeaturesintheimagestoseehowariverhas migrated,howanareaisflooded,ortoseeifatumoris
option, blockstheMATLABcommandlineuntil controlpointshavebeenselectedandreturnsthesetsof controlpointsselectedintheinputimageandthebaseimage option, asareturnvalues.Ifyoudonotusethe returnscontrolimmediatelyandyourscriptwill continuewithoutallowingtimeforcontrolpointselection.In option, doesnotreturn addition,withoutthe thecontrolpointsasreturnvalues.Foranexample,seethe referencepage. BacktoTop
orthophoto,eachpixelcentercorrespondstoadefinite geographiclocation,andeverypixelis1metersquareinmap units. ,a Theimagetoberegisteredis digitalaerialphotographsuppliedbymPower3/Emerge,and isavisible-colorRGBimage.Theaerialimageis geometricallyuncorrected:itincludescameraperspective, terrainandbuildingrelief,internal(lens)distortions,andit doesnothaveanyparticularalignmentorregistrationwith respecttotheearth. ThefollowingexamplereadsbothimagesintotheMATLAB workspaceanddisplaysthemusing