One of the drawbacks of using global motion estimation in motion-compensated video coding is the overhead associated with the number and accuracy of motion parameters. Although prediction gain increases with increased motion accuracy, higher accuracy is not affordable since this increases motion bit rate as well. Therefore, an efficient global motion vector coding algorithm is necessary for improving the prediction gain. In this paper, we present a new solution for global motion vector coding which finds the best motion accuracy for each frame. Given a fixed motion bit-rate for global motion vectors, the proposed algorithm allocates the bits among differential motion vectors optimally by a best-accuracy search method. Secondly, we propose a novel mean square error modeling approach which reduces the complexity of the optimal search algorithm. The experimental results show that the proposed algorithm give higher peak signal-to-noise ratio (PSNR) compared to the global motion vector coding algorithm proposed in MPEG-4 standard.
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