Improved lifting scheme for block subband coding

Time-varying orthogonal filter bank approaches for block wavelet transform (WT) and wavelet packet (WP) based subband coding methods have two common problems: (1) severe block effects in subbands caused by sudden level changes at the boundaries; (2) more complicated reconstruction filterbanks than the decomposition filterbank due to a larger number of switching operations. The recently introduced lifting scheme is based on the idea of generating biorthogonal systems using simple and invertible stages. As such the lifting scheme is suitable for block subband coding. However, the lifting scheme continues to exhibit block effects for even-length blocks. This is due to the big prediction errors at right boundaries caused by extrapolation. In this paper we present an improved lifting scheme (ILS) for independent block subband coding. The ILS is free of block effects and the boundary treatments are more efficient. The reconstruction has the same simplicity as the decomposition.