Method and apparatus for coding/decoding image signal providing accurate determination of an image contour and efficient compression coding

摘要

On the coding side of the apparatus, an image signal is divided into an upper signal for coarsely designating a level of the image signal and a lower signal for finely designating the level of the image signal. The upper signal is then coded. A reference signal for coding the lower signal is selected. The lower signal is coded by referring to the selected reference signal. The coded upper and the lower signals are synthesized, and the synthesized code is output as a code corresponding to the image signal. On the decoding side of the apparatus, the synthesized code is decoded into a code corresponding to the upper signal and a code corresponding to the lower signal. The code corresponding to the upper signal is decoded into an upper signal. A reference signal for decoding the code corresponding to the lower signal is selected. The code corresponding to the lower signal is decoded into a lower signal by referring to the selected signal. The decoded upper and lower signals are synthesized to obtain the image signal.