10.2.6MoreAdvancedTechniquesforEdgeDetectionTheMarr-HildrethedgedetectorTheMarr-HildrethedgedetectorTheMarr-HildrethedgedetectorTheMarr-HildrethedgedetectorStep1:filtertheinputimagewithGaussianlowpassfilter;Step2:ComputetheLaplacianoftheimageresultingfromstep1;Step3:findthezerocrossingoftheimagefromstep2;

CannyedgedetectorStep1:SmooththeinputimagewithaGaussianfilter;Step2:Computethegradientmagnitudeandangleimage;Step3:Applynonmaximasuppressiontothegradientmagnitudeimage;Step4:usedoublethresholdingandconnectivityanalysistodetectandlinkedge;10.3Thresholding10.3.1FoundationThebasicofintensitythresholding10.3Thresholding10.3Thresholding10.3Thresholding10.3.2BasicGlobalThresholdingStep1:selectaninitialestimatefortheglobalthreshold,TStep2:segmenttheimageusingTin2Groups:G1={(x,y)|f(x,y)>Thr},G2={(x,y)|f(x,y<=thr)}Step3:computetheaverageintensityvaluesm1forG1andm2forG2Step4:computeanewthresholdvalue:T=(m1+m2)/2;Repeatstep2tostep4,untilT_new–T_old<ΔT10.3.2BasicGlobalThresholdingLocalThreshodingConnected-componentlabelingInputOutput0000000000ff00ffff00ffff0ffff00ffff00ffff000000ffff00ffffff0ffff00ffff000ff000000000000000000010022001102200110022000000220033302200330002000000000Connected-componentlabelingRecursivefunctionvoidLabel(byte[,]f,intx,inty,byteL){ f[x,y]=L;

if(f[x+1,y]==255)Label(f,x+1,y,L); if(f[x-1,y]==255)Label(f,x-1,y,L); if(f[x,y+1]==255)Label(f,x,y+1,L); if(f[x,y-1]==255)Label(f,x,y-1,L);}Connected-componentlabelin