Optimized bit allocation for scalable wavelet video coding

The hybrid coding scheme is employed in all established coding standards. A forward motion vector field is estimated and applied for motion compensation. The remaining prediction error and the motion vectors are transmitted to the decoder. The discrete cosine transform is used for transform coding of the prediction error. The extension of this coding scheme to scalability is not easily achieved and the performance of standard video coders when using scalability options can often be reduced to the performance of simulcast coding. In this paper a hierarchical spatial scalable wavelet video coder is presented. A backward motion compensation scheme is used and no motion vectors have to be transmitted. In this coding scheme the lowpass band of the decomposition is coded first without motion compensation using DPCM. The coarser levels of the signal decomposition which are known to both, the encoder and the decoder, are then employed for motion estimation of the next levels. Due to the hierarchical structure of the presented scheme the impact of quantization is strongly interdependent between the decomposition levels. In contrast to still image coding quantization affects the reconstruction quality as well as the motion estimation and motion compensation efficiency. In this paper the bit allocation for the decomposition levels of the hierarchical wavelet video coder is investigated.