REVERSIBLE SUBBAND CODING OF IMAGES

In conventional 1D filter banks used for reversible subband coding of gray-level still images, the high-band signals are extrapolative or in terpolative prediction error signals, the former using one side of the pixels alone and the latter using two sides of the pixels but with le vels four times that of the input signals. This paper proposes a rever sible 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 l evels twice that of the input signal as the high-band signals. This pa per also describes the design of nonseparable filter banks which predi ct a pixel in question by using four pixels around the point. The comp ression efficiency of the proposed method has been compared with the c onventional method by using real images. The results show the followin g: 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 reversi ble predictive coding; the separable filter banks have a higher compre ssion 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.