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ForegrounddetectionusingGaussianmixturemodels
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vision.ForegroundDetectorSystemobject
Package:vision
DescriptionTheForegroundDetectorSystemobjectcomparesacolororgrayscalevideoframetoabackgroundmodeltodeterminewhetherindividualpixelsarepartofthebackgroundortheforeground.Itthencomputesaforegroundmask.Byusingbackgroundsubtraction,youcandetectforegroundobjectsinanimagetakenfromastationarycamera.
Note:StartinginR2016b,insteadofusingthestepmethodtoperformtheoperationdefinedbytheSystemobject,youcancalltheobjectwitharguments,asifitwereafunction.Forexample,y=step(obj,x)andy=obj(x)performequivalentoperations.
Constructiondetector=vision.ForegroundDetectorreturnsaforegrounddetectorSystemobject,detector.Givenaseriesofeithergrayscaleorcolorvideoframes,theobjectcomputesandreturnstheforegroundmaskusingGaussianmixturemodels(GMM).
detector=vision.ForegroundDetector(Name,Value)returnsaforegrounddetectorSystemobject,detector,witheachspecifiedpropertynamesettothespecifiedvalue.NamecanalsobeapropertynameandValueisthecorrespondingvalue.YoucanspecifyseveralnamevaluepairargumentsinanyorderasName1,Value1,,NameN,ValueN.
CodeGenerationSupport
SupportsMATLAB Functionblock:No
UsingMATLABhosttarget:Generatesplatformdependentlibrary
NotusingMATLABhosttarget:GeneratesportableCcode
SystemObjectsinMATLABCodeGeneration.
CodeGenerationSupport,UsageNotes,andLimitations.
Properties
Adaptlearningrate,specifiedasthecommaseparatedpairconsistingof'AdaptLearningRate'andalogicalscalar'true'or'false'.ThispropertyenablestheobjecttoadaptthelearningrateduringtheperiodspecifiedbytheNumTrainingFramesproperty.Whenyousetthispropertytotrue,theobjectsetstheLearningRatepropertyto1/(currentframenumber).Whenyousetthispropertytofalse,theLearningRatepropertymustbesetateachtimestep.
Numberofinitialvideoframesfortrainingbackgroundmodel,specifiedasthecommaseparatedpairconsistingof'NumTrainingFrames'andaninteger.WhenyousettheAdaptLearningRatetofalse,thispropertywillnotbeavailable.
Learningrateforparameterupdates,specifiedasthecommaseparatedpairconsistingof'LearningRate'andanumericscalar.Specifythelearningratetoadaptmodelparameters.Thispropertycontrolshowquicklythemodeladaptstochangingconditions.Setthispropertyappropriatelytoensurealgorithmstability.
AdaptLearningRateAdaptlearningrate'true'(default)|'false'
NumTrainingFramesNumberofinitialvideoframesfortrainingbackgroundmodel150(default)|integer
LearningRateLearningrateforparameterupdates0.005(default)|numericscalar
javascript:void(0);javascript:void(0);http://www.mathworks.com/help/vision/gs/use-system-objects-in-matlab-code-generation.htmlhttp://www.mathworks.com/help/vision/ug/code-generation-support-usage-notes-and-limitations-for-functions-classes-and-system-objects.htmlhttp://www.mathworks.com/help/vision/ref/vision.foregrounddetector-class.html#bsy_s0n-5http://www.mathworks.com/help/vision/ref/vision.foregrounddetector-class.html#bsy_s0n-5
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WhenyousetAdaptLearningRatetotrue,theLearningRatepropertytakeseffectonlyafterthetrainingperiodspecifiedbyNumTrainingFramesisover.
WhenyousettheAdaptLearningRatetofalse,thispropertywillnotbeavailable.Thispropertyistunable.
Thresholdtodeterminebackgroundmodel,specifiedasthecommaseparatedpairconsistingof'MinimumBackgroundRatio'andanumericscalar.Setthispropertytorepresenttheminimumoftheaprioriprobabilitiesforpixelstobeconsideredbackgroundvalues.Multimodalbackgroundscannotbehandled,ifthisvalueistoosmall.
NumberofGaussianmodesinthemixturemodel
NumberofGaussianmodesinthemixturemodel,specifiedasthecommaseparatedpairconsistingof'NumGaussians'andapositiveinteger.Typicallythisvalueis3,4or5.Setthisvalueto3orgreatertobeabletomodelmultiplebackgroundmodes.
Initialmixturemodelvariance,specifiedasthecommaseparatedpairconsistingof'InitialVariance'andasanumericscalarorthe'Auto'charactervector.
ImageDataType InitialVariance
double/single (30/255)^2
uint8 30^2
Thispropertyappliestoallcolorchannelsforcolorinputs.
Methodsclone Createforegrounddetectorwithsamepropertyvalues
getNumInputs Numberofexpectedinputstostepmethod
getNumOutputs Numberofoutputsfromstepmethod
isLocked
Lockedstatusforinputattributesandnontunableproperties
release Allowpropertyvalueandinputcharacteristicschanges
reset ResettheGMMmodeltoitsinitialstate
step DetectforegroundusingGaussianmixturemodels
Examples
Createsystemobjectstoreadfile.
videoSource=vision.VideoFileReader('viptraffic.avi',...'ImageColorSpace','Intensity','VideoOutputDataType','uint8');
Settingframesto5becauseitisashortvideo.Setinitialstandarddeviation.
MinimumBackgroundRatioThresholdtodeterminebackgroundmodel0.7(default)|numericscalar
NumGaussiansNumberofGaussianmodesinthemixturemodel5(default)|positiveinteger
InitialVarianceInitialmixturemodelvariance'Auto'(default)|numericscalar
DetectMovingCarsInVideo
OpenScript
javascript:void(0);http://www.mathworks.com/help/vision/ref/vision.foregrounddetector-class.html#bsy_s0n-5http://www.mathworks.com/help/vision/ref/vision.foregrounddetector-class.html#bsy_s0n-5http://www.mathworks.com/help/vision/ref/vision.foregrounddetector-class.html#bsy_s0n-5http://www.mathworks.com/help/vision/ref/vision.foregrounddetector.clone.htmlhttp://www.mathworks.com/help/vision/ref/vision.foregrounddetector.getnuminputs.htmlhttp://www.mathworks.com/help/vision/ref/vision.foregrounddetector.getnumoutputs.htmlhttp://www.mathworks.com/help/vision/ref/vision.foregrounddetector.islocked.htmlhttp://www.mathworks.com/help/vision/ref/vision.foregrounddetector.release.htmlhttp://www.mathworks.com/help/vision/ref/vision.foregrounddetector.reset.htmlhttp://www.mathworks.com/help/vision/ref/vision.foregrounddetector.step.htmlmatlab:openExample('vision/TrackCarsExample')
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detector=vision.ForegroundDetector(...'NumTrainingFrames',5,...'InitialVariance',30*30);
Performblobanalysis.
blob=vision.BlobAnalysis(...'CentroidOutputPort',false,'AreaOutputPort',false,...'BoundingBoxOutputPort',true,...'MinimumBlobAreaSource','Property','MinimumBlobArea',250);
Insertaborder.
shapeInserter=vision.ShapeInserter('BorderColor','White');
Playresults.Drawboundingboxesaroundcars.
videoPlayer=vision.VideoPlayer();while~isDone(videoSource)frame=step(videoSource);fgMask=step(detector,frame);bbox=step(blob,fgMask);out=step(shapeInserter,frame,bbox);step(videoPlayer,out);end
Releaseobjects.
release(videoPlayer);release(videoSource);
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References[1]P.Kaewtrakulpong,R.Bowden,AnImprovedAdaptiveBackgroundMixtureModelforRealtimeTrackingwithShadowDetection,InProc.2ndEuropeanWorkshoponAdvancedVideoBasedSurveillanceSystems,AVBS01,VIDEOBASEDSURVEILLANCESYSTEMS:ComputerVisionandDistributedProcessing(September2001)
[2]Stauffer,C.andGrimson,W.E.L,AdaptiveBackgroundMixtureModelsforRealTimeTracking,ComputerVisionandPatternRecognition,IEEEComputerSocietyConferenceon,Vol.2(06August1999),pp.2246252Vol.2.
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