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Vertex and face permutation order compression for efficient animation support

In MPEG-4, 3D mesh coding (3DMC) achieves 40:1 to 50:1 compression ratio over 3-D meshes (in VRML IndexedFaceSet representation) without noticeable visual degradation. This substantial gain comes not for free: it changes the vertex and face permutation order of the original 3-D mesh model. This vertex and face permutation order change may cause a serious problem for animation, editing operation, and special effects, where the original permutation order information is critical not only to the mesh representation, but also to the related tools. To fix this problem, we need to transmit the vertex and face permutation order information additionally. This additional transmission causes the unexpected increase of the bitstream size. In this paper, we proposed a novel vertex and face permutation order compression algorithm to address the vertex and face permutation order change by the 3DMC encoding with the minimal increase of side information. Our proposed vertex and face permutation order coding method is based on the adaptive probability model, which makes allocating one fewer bits codeword to each vertex and face permutation order in every distinguishable unit as encoding proceeds. Additionally to the adaptive probability model, we further increased the coding efficiency of the proposed method by representing and encoding each vertex and face permutation order per connected component (CC). Simulation results demonstrated that the proposed algorithm can encode the vertex and face permutation order losslessly while making up to 12% bit-saving compared with the logarithmic representation based on the fixed probability model.