说明：  [knew,m,n]=contour_b_trial_2(a,row,col) knew=contour image m=contour background pixels n=contour object pixels ch=contour_code_2(m) ch=contour code [k8,m8]=eightneighbour(k,n) k8=contour image containing eight neighbourhood m8=contour pixels [k4,m4]=fourneighbour2(k,n) k4=contour image containing four neighbourhood m4=contour pixels press pause after each plot to continue