This paper proposes a new ADPCM method for image coding called directional ADPCM which can remove more redundancy from the image signals than the conventional ADPCM. The conventional ADPCM calculates the two-dimensional prediction coefficients by using the correlation functions followed by solving the Yule-Walker equation. Actually, the quantities of correlation functions to be the approximation of the correlation function. However, the block size is limited by the error accumulation effect during packet transmission. Using small block may induce the unregulated prediction coefficients. Therefore, we need to develop the directional ADPCM system to overcome such a problem and to have better prediction result. Our directional ADPCM utilized the fan- shape filters to obtain the energy distribution in four directions and then determines the four directional prediction coefficient. All the fan-shape filters are designed by using the singular value decomposition (SVD) method, the two-dimensional Hilbert transform technique, and the frequency weighting concept. In the experiments, we illustrate that the M.S.E. for the directional ADPCM is less than that of the conventional ADPCM.
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