Adaptive bit allocation and resolution selection techniques for motion estimation in wavelet-based video coder

Wavelet transform is an important tool for image and video coding applicati ons. Several motion estimation techniques have been proposed in the wavelet domain. Coarse-to-fine motion estimation techniques generally have a lower complexity, but they may lead to inaccurate motion estimation if the coars e motion estimation is erroneous; On the other hand, pixel-domain motion es timation techniques provide a superior estimation, but at a higher complexi ty. In this paper, an efficient video coder in the wavelet domain is propos ed. First, an adjustable resolution selection for motion estimation is prop osed where a low-pass subband at an appropriate resolution is employed for coarse motion estimation. The motion vectors corresponding to subbands of o ther resolutions are then predicted from these coarse motion vectors. When motion vectors are predicted from a lower- to a higher-resolution subband, the predicted motion vectors are further refined using a small search windo w. Second an adaptive bit allocation technique is proposed where the bits a re allocated optimally between the motion vectors and the displaced frame d ifference. This allocation is performed by minimizing a cost function based on the Lagrange multiplier method. Simulation results show that the propos ed video coder provides a good coding performance compared to other multire solution techniques proposed in recent literature.