Using multiple global motion models for improved block-based video coding
A novel motion representation and estimation scheme is presented that leads to improved coding efficiency of block-based video coders like, e.g., H.263. The proposed scheme is based on motion-compensated prediction from more than one reference frame. The reference pictures are warped or globally motion-compensated versions of the previous frame. Affine motion models are used as warping parameters approximating the motion vector field. Motion compensation is performed using standard block matching in the multiple reference frames buffer. The frame reference and the affine motion parameters are transmitted as side information. The approach is incorporated into an H.263-based video codec at minor syntax changes and embedded into a rate-constrained motion estimation and macroblock mode decision frame work. In contrast to conventional global motion compensation, where one motion model is transmitted, we show that multiple global motion models are of benefit in terms of coding efficiency. Significant coding gains in comparison to TMN-10, the test model of H.263+, are achieved that provide bit-rate savings between 20% and 35% for the various sequences tested.