MOTION-COMPENSATED PREDICTION USING NODAL-BASED DEFORMABLE BLOCK MATCHING

One well-known deficiency of the block matching algorithm (BMA) is that it cannot handle nontranslational motion within a block. This paper proposes a nodal-displacement-based deformation model. It assumes that a selected number of control nodes in a block can move freely, and that the displacement of any interior point can be interpolated from nodal displacements. This model includes the translational model as a special case with a single node and can characterize increasingly more complex deformation by the use of more nodes. Of particular importance is the four-node-based rectangle to quadrangle mapping, which covers essentially all possible 2D deformations caused by 3D motions over a reasonably small block. A deformable block matching algorithm (DBMA) is developed for the estimation of nodal displacements. It is a gradient-based search algorithm and each iteration requires the solution of a simple linear equation. A hybrid three-mode method is further proposed, which chooses among the BMA and DBMA, both without error correction, and the BMA with error correction using a DCT coding method (BMA-DCT). The DBMA and the three-mode method have been simulated for the case of the four-node-based mapping. In comparison with the BMA-DCT, the reduction of prediction errors by the DBMA outweighs the increase in required bits for specifying motion. At similar bit rates, the DBMA has yielded better image quality than the BMA-DCT. On the other hand, the three-mode method can significantly reduce the bit rate while maintaining a similar quality, at the expense of a slight increase in the computational cost. (C) 1995 Academic Press, Inc.