Edge-based subband VQ techniques for images and video
A key issue in subband coding is the efficient compression of the less informative but perceptually important upper frequency bands of the decomposed image. A new approach capable of effectively encoding the upper-bands is described. An intra-band vector quantization (VQ) technique is employed for compression of the base-band while the upper frequency bands are encoded by a hierarchical inter-band VQ method. The proposed inter-band vector quantization scheme exploits the redundancies that exist between pels of significant perceptual importance across the upper frequency bands of the same resolution. Such pels are observed to be at or around the edge-locations, displaying similar discontinuity behavior across the subbands. Therefore, an edge-detector is applied on the reconstructed base-band to extract the edge locations, and as a result no overhead information is transmitted to identify the position of these pels in the upper-bands. Furthermore, a residual subband, being the difference between the original base-band of each layer and its encoded version, is incorporated in the proposed inter-band VQ model. Thus, the proposed interband VQ scheme is simply the vector quantization of pixels across the upper-bands together with their corresponding residual band. Compression results are presented for both digital images and video sequences which demonstrate high subjective visual qualities. >