RATE-DISTORTION OPTIMIZATION OF HIERARCHICAL DISPLACEMENT-FIELDS

The displacement vector field for motion-compensated coding of image s equences is represented and coded using a hierarchy of displacement ve ctor fields over successively finer sampling grids. An efficient metho d based on the generalized Breiman-Friedman-Olshen-Stone (BFOS) tree-p runing algorithm is used to find a variable-depth hierarchy that satis fies a given bit rate or distortion constraint. The variable-depth hie rarchy corresponds to using a nonuniformly sampled displacement held f or motion compensation. The proposed scheme is compared with conventio nal fixed-block-size block-matching motion compensation. The motion in formation bit rate or the motion-compensation residual energy of the c onventional scheme serves as the constraint, Simulation results show t hat the proposed scheme reduces the residual energy by between 0.6-1.5 dB, or the bit rate by 19-54%, while using only 40-100% of the comput ational complexity of the conventional scheme. The prediction image se quence produced by the hierarchical scheme offers much better viewing quality.