A preliminary evaluation of 3D mesh animation coding techniques
Mathematical Methods in Pattern and Image Analysis
This paper provides an overview of the state-of-the-art techniques recently developed within the emerging field of dynamic mesh compression. Static encoders, wavelet-based schemes, PCA-based approaches, differential temporal and spatio-temporal predictive techniques, and clustering-based representations are considered, presented, analyzed, and objectively compared in terms of compression efficiency, algorithmic and computational aspects and offered functionalities (such as progressive
... on, scalable rendering, computational and algorithmic aspects, field of applicability...). The proposed comparative study reveals that: (1) clustering-based approaches offer the best compromise between compression performances and computational complexity; (2) PCA-based representations are highly efficient on long animated sequences (i.e. with number of mesh vertices much smaller than the number of frames) at the price of prohibitive computational complexity of the encoding process; (3) Spatio-temporal Dynapack predictors provides simple yet effective predictive schemes that outperforms simple predictors such as those considered within the interpolator compression node adopted by the MPEG-4 within the AFX standard; (4) Wavelet-based approaches, which provide the best compression performances for static meshes show here again good results, with the additional advantage of a fully progressive representation, but suffer from an applicability limited to large meshes with at least several thousands of vertices per connected component. INTRODUCTION Dynamic 3D content becomes a more and more present feature within nowadays multimedia applications, extensively exploited within the world of games, virtual and augmented reality systems, industrial simulation, and 3D CGI (Computer Generated Imagery) animation films that recently have known a world-wide success. Within this context, the new economic challenges concern the elaboration and the seamless integration of efficient 3D representation technologies. Besides the traditional compression efficiency requirement, such dynamic 3D representations should enable new functionalities, such as real-time visualization on multiple terminals, progressive transmission over various networks, and scalable rendering with multiple Levels of Detail (LODs). The progressive transmission functionality concerns the bitstream adaptation to different, fixed or mobile communication networks with various bandwidths. Here, the decoder can start displaying a coarse approximation of the animation sequence when some baseline, minimal information is received. A refinement process is then applied to this coarse representation in order to obtain progressively finer LODs and gradually improve the visual quality of the decoded animation sequence. The scalable rendering functionality concerns the bitstream adaptation to terminals (e.g., desktop computers, laptops, PDAs, mobilephones...) of various complexities with different memory and computational capacities, under real-time visualization constrains. Here, decimation-based approaches 15 are generally adopted in order to obtain simplified representation that are visually close to the original and which can be rendered at a low computation time. Within this challenging applicative framework, the issue of elaborating efficient compression methodologies for memory consuming 3D animated meshes becomes of a crucial importance.