Image encoding method and apparatus, image decoding method and apparatus, and programs therefor

When the entire image is divided into regions, each of which is subjected to predictive encoding while predicting an image signal by using an independent method assigned to the region, the object number and a representative pixel value for each object are predicted utilizing spatial continuity for the presence of the object, and also using decoded pixel values of a previously-processed neighbor region adjacent to a processing region. Accordingly, it is possible to reduce the amount of code required for encoding the object number in the processing region or the pixel value as a representative of each object in the processing region, where these encoded items are required in highly accurate image signal prediction which can handle any object shape by utilizing the pixel value as a representative of each object in the processing target region and information for identifying the object assigned to each pixel in the processing region. Therefore, efficient image encoding can be implemented. Since the employed decoded pixel values of pixels in a previously-decoded neighbor region are common information between the encoding and decoding sides, appropriate prediction can be performed even in the case where one of multiple image signal prediction modes is selected for each region, like in H.264.