Motion modeling with separate quad-tree structures for geometry and motion

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 quadtree structures. Recent work into quad-tree representations have also highlighted the benefits of leaf merging. We extend the leaf merging paradigm to incorporate separate tree structures for boundary geometry and motion. To achieve an efficient joint representation we introduce polynomial motion models and piecewise linear boundary geometry to our quad-tree structures. Experimental results show that the approach taken in this paper provides significant improvement over previous quad-tree based motion representation schemes.