1. A method for encoding an image frame including L objects in an input image signal, L being a non-negative integer, comprising the steps of: (a) extracting L contours of the L objects; (b) selecting a set of vertices which fits each contour; (c) determining an initial vertex of each contour in said set of vertices; (d) grouping the L contours into at most L groups of contours according to a predetermined criterion; (e) selecting a first initial vertex among the initial vertices of the contours included in each group of contours; (f) encoding absolute addresses of the first initial vertices of all the groups of contours, the absolute address of a vertex representing position of the vertex in the image frame; (g) encoding displacements of the rest of the initial vertices for all the group of contours, wherein a displacement of an initial vertex is calculated with respect to a preceding initial vertex; and (h) rendering the encoded absolute addresses and the displacements as encoded initial vertex data.