Reversible subband coding of images

Abstract

AbstractIn conventional 1D filter banks used for reversible subband coding of gray‐level still images, the high‐band signals are extrapolative or interpolative prediction error signals, the former using one side of the pixels alone and the latter using two sides of the pixels but with levels four times that of the input signals.This paper proposes a reversible subband coding method which has a high compression efficiency by reducing the entropy of the high‐band signal. This method employs 1D filter banks which use interpolative prediction error signals having levels twice that of the input signal as the high‐band signals.This paper also describes the design of non‐separable filter banks which predict a pixel in question by using four pixels around the point. The compression efficiency of the proposed method has been compared with the conventional method by using real images. The results show the following: the entropy of the proposed method is smaller than the conventional method by 0.1 to 0.5 bits/pel; some samples processed by the proposed method show a higher compression efficiency than those in the reversible predictive coding; the separable filter banks have a higher compression efficiency than the nonseparable filter banks (both based on the proposed method); and the reduced images using the proposed separable method with a lowpass filter have many taps to suppress aliasing.