Improvement of Performance in DCT and SSKF Image Coding Systems for Negatively-Correlated Signal Input by Signal Modulation


IEICE TRANSACTIONS on Communications   Vol.E78-B   No.11   pp.1529-1542
Publication Date: 1995/11/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Source Encoding
image coding,  DCT,  SSKF,  negative correlation,  signal modulation,  

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This paper deals with the improvement of performance in the transform and subband image coding systems with negatively-correlated input signal. Using a more general source model than the AR(1) model as an input, the coding performance for the transform and subband coding schemes is evaluated in terms of the coding gain over PCM. The source model used here has such resonant band characteristics that its power spectrum has a peak at some frequency between 0 and π/2 for positive autocorrelation and between π/2 and π for negative autocorrelation. It is shown that coding schemes are classified into two classes; one has the pairwise mirror-image property in their filter banks and performs symmetrically regardless of the sign of the autocorrelation, and the other has no that property and performs asymmetrically with inferior performance for negative autocorrelation. Among the well-known transform and subband coding schemes, the DHT and QMF coding systems belong to the former class and the DCT and SSKF coding systems to the latter. In order to remedy the inferior performance, we propose the method in which one modulates the negatively-correlated signal sequences by the alternating sign signal with unity magnitude (-1)n to convert them into positively-correlated sequences. The algorithms are presented for the DCT and SSKF image coding systems with the adaptive signal modulation. In the DCT coding systems, we are particularly concerned with the DCT-based hierarchical progressive coding mode of operation, since the signal modulation works well for that coding mode. The SSKF image coding system has the regular quad-tree structure with three stages. The simulation results for test images show that our method can successfully be applied to the images with a considerable amount of energy in the frequency range higher than π/2 in horizontal or vertical direction, such as fingerprints and textile patterns sampled at a rate close to the Nyquist rate. The paper closes with a brief introduction to the modification of our DCT-based method.