1. A method for encoding a contour of an object expressed in a video signal, comprising the steps of: (a) detecting a centroid for the contour of the object by averaging pixel positions on the contour; (b) determining a set of primary vertices on the contour based on the centroid, the contour being approximated by connecting each pair of immediate adjacent primary vertices with a straight line; and (c) encoding the set of primary vertices and the centroid to thereby provide a digitally coded contour signal, wherein said step (b) includes the steps of: (b11) drawing M number of radial lines, including a reference radial line formed in a predetermined manner, from the centroid, wherein the angle between each pair of immediate adjacent radial lines is (2.pi./M) radian with M being an integer larger than 1; (b12) determining the set of primary vertices, each primary vertex representing an intersection point between the contour and a radial line; and (b13) indexing the set of primary vertices starting from the primary vertex for the reference radial line.