In this paper we present an efficient very low bit-rate coder for CIF image sequences at 10 frames/s. The proposed algorithm performs motion compensation using a second-order geometric transformation and a quadtree structure. High compression ratios have been reached adapting the features of the transformation and the block size to the motion. A linear transformation is used when there is translational motion, whereas a non-linear transformation is applied when a block has to be warped. In addition the block size is increased in homogeneous zones and reduced in detailed moving zones. Simulation results show that the proposed coding method improves the predicted image quality and reduces the blocking artifacts with respect to traditional hybrid block-based techniques.
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