Effective sampling points for two-channel spline image coding

Numerous image coding techniques have been proposed over the last decade, among which a discrete cosine transform (DCT) is a key technique adapted in JPEG as a standard. Although DCT shows a good coding performance, the problem of block distortion or blur of details is often observed in the case of a low bit rate. It is therefore difficult to obtain a high-quality image with only a few bits. By using multi-channel coding, however, an image can be divided into spatial components and each of the components is encoded according to its property, which enables the resolution of eyesore noise such as block distortion. However, its performance is not as good as that of JPEG's. Y. Yanagihara (1997) proposed a two-channel coding technique using spline interpolation. In this technique, a low-frequency component is represented by a smooth spline surface and a high-frequency component is represented as the difference between the original image and the low-frequency image. Yanagihara showed that this method is superior to JPEG for compressing images while maintaining a high quality. We discuss ways of sampling points for the spline surface in order to improve the performance in Yanagihara's technique.