Hierarchical 2-D mesh representation, tracking, and compression for object-based video

This paper proposes methods for designing, tracking and coding hierarchical two-dimensional (2-D) content-based mesh representations. The design proce dure consists of constructing a fine-to-coarse hierarchy of Delaunay meshes , using image- and shape-based criteria for mesh geometry simplification. H ierarchical tracking employs a coarse-to-fine strategy with mesh-based moti on vector optimization, We introduce new techniques to maintain the initial mesh hierarchy and topology during tracking by imposing certain constraint s at each stage of the procedure, The hierarchical compression technique is based on a nearest neighbor ordering of mesh node points. This ordering se rves to identify the mesh boundary nodes as well as establish spatial predi ctors for differential coding of node coordinates and motion vectors, The p roposed hierarchical mesh representation, which has applications in object- based video manipulation, indexing, and compression, provides improved trac king performance (compared to a nonhierarchical representation) and allows progressive (scalable) transmission of the object geometry (including shape ) and motion information, as well as variable level-of-detail rendering, Ex perimental results are presented to compare the tracking and compression pe rformance of hierarchical versus nonhierarchical mesh representations and t o demonstrate the tradeoff between image quality and mesh bit rate for 2-D mesh-based video object rendering.