Patent ID: 8155204

Claim:
An image decoding apparatus comprising: a frame memory capable of storing an image decoded in the past as a reference picture in order to use a part of the image decoded in the past as a reference block in a picture being presently decoded, the reference picture being stored in a field structure in which top lines in the reference picture are stored in a top area and bottom lines in the reference picture are stored in a bottom area separately; a reference picture reconstructing device configured to selectively copy and store an uppermost top line or an uppermost bottom line in the reference picture to areas on the uppermost top line and the uppermost bottom line in the reference picture in the top area and the bottom area respectively in the frame memory, and to selectively copy and store a lowermost top line or a lowermost bottom line in the reference picture to areas under the lowermost top line and the lowermost bottom line in the reference picture in the top area and the bottom area respectively in the frame memory; a reading/transferring device configured to read and transfer image data included in a rectangular area of the reference block defined in correspondence with motion vector information indicative of positional relation between a picture being presently decoded and the reference picture, in image data of the top line and the bottom line of the reference picture and the copied top and bottom lines; and a reference block forming device configured to form the reference block by using the transferred image data and, in the case where all of the rectangular area of the reference block cannot be formed only by the transferred image data, by copying or address-converting a part of the transferred image data.