SUMMARYIn this paper, a directional filter is newly designed that extracts the edges in a particular direction using the discrete cosine transform (DCT). The filter is then applied to the two-channel image coding. Especially, the cut-off frequency response of the directional filter, which greatly affects the quality of the reconstructed image near the edge, is investigated and improved so that the ideal edge waveform can be extracted. In the proposed coding scheme, the original image is separated into the low-frequency components and the high-frequency components, according to the principle of the two-channel image coding.The low-frequency component is the smooth component with smaller block distortions. The coding performance for the coding scheme of the low-frequency component is discussed from the viewpoint of the coding rate and the image quality. The highfrequency component is separated into the directional images containing edges in particular directions, and the results are encoded. By applymg this scheme, little block distortion is produced even for the low bit rate, and the visually satisfactory image with clear edges can be reconstructed. The usefulness of the proposed scheme also is verified by a computer simulation compared to the conventional coding schemes.
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