An enhanced block-based hierarchical image coding scheme

A block-based, two-layer hierarchical image coding scheme codes a down-sampled version of the original image first, and then the residue between the original one and a reconstructed version that is interpolated from the upper layer. When the residual layer is coded at a lower quality as compared to its upper layer, it often happens that all pixels in the upper layer will be deteriorated if the corresponding coded residuals are added into them. In this paper, we demonstrate that there exists a critical region for each image such that the deterioration indeed happens and this region includes nearly all typical bit-rates used in practice. To avoid this problem, we first propose a 'naive' solution and then apply an advanced quantization technique to handle the residual layer. To verify the effectiveness, we conduct extensive tests to show that the gap between the hierarchical coding scheme and its single-level counterpart (which is typically around 2∼3 dB in the two-layer scenario) has been filled up by a rather big percentage (about 30∼50%).