Efficient encoding of dense motion fields for motion-compensated video compression

A dense motion field provides a number of advantages over the traditional block-based motion models in interpreting the temporal correlation between video frames. However, until now, its application to motion-compensated video coding has been limited due to the inhibitive rate needed to encode the motion field. We present an efficient scheme for encoding a dense motion field which makes it possible to apply it in a forward motion-compensated video coding framework. A multi-scale motion field is first estimated to represent the motion at different scales. This full multi-scale motion field is then reduced adaptively by a tree pruning algorithm, resulting in a motion field that is represented at different scales from region to region. The pruned motion vector components are coded by a backward context-based arithmetic coding scheme. The motion vector encoding scheme is then incorporated into a complete video codec in which a much greater percentage of the overall bit-rate is allocated to the motion information (+30%). Simulations show that such a system provides substantial improvements over standard block-based coders