对二值图像边界进行跟踪，对边缘进行判断，然后沿着边缘进行跟进- C = CONTOUR_FOLLOWING(BW) takes BW as an input. BW is a binary array

　containing the image of an object ( 1 : foreground,　0 : background). It

　returns a circular list (N x 2, C(1,:)=C(end,:)) of the

　(row,column)-coordinates of the object s contour, in the order of

　appearence (This function was inspired from the freeman contour coding

　algorithm).