Scalable Modeling of Motion and Boundary Geometry With Quad-Tree Node Merging

Quad-tree structures are often used to model motion between frames of a video sequence. However, a fundamental limitation of the quad-tree structure is that it can only capture horizontal and vertical edge discontinuities at dyadically related locations. To address this limitation, recent work has focused on the introduction of geometry information to nodes of tree structured motion representations. In this paper we explore modeling boundary geometry and motion with separate quad-tree structures; thereby enabling each attribute to be refined separately. Recent work into quad-tree representations has also highlighted the benefits of leaf merging. We extend the leaf merging paradigm to incorporate both geometry and motion attributes. We also explore resolution scalability of the merged dual tree representation and present experimental results which demonstrate both rate-distortion and scabalility performance. Theoretical investigations conducted in this paper reveal that to achieve optimal rate-distortion behavior, quad-tree motion models need to incorporate both geometry information and node merging.