ENCODING METHOD AND DECODING METHOD OF MOVING IMAGE

PROBLEM TO BE SOLVED: To provide a method of preventing accumulation of rounding errors occurring by coprimary interpolation performed in motion compensation, in an image encoding method where the intensity value of brilliance or color difference is quantized to an integer.SOLUTION: With regard to a P frame performing one-way motion compensation, two types of frames, i.e., P+ frames 503, 507 where a value obtained by adding 0.5 to an integer is rounded up, and P- frames 505, 509 where a value obtained by adding 0.5 to an integer is rounded down are prepared. A step for synthesizing the prediction images of decoded images, and a step for decoding the decoded image by using the prediction image are included. When the decoded image is a P frame, the step for synthesizing the prediction images performs motion compensation using plus rounding or motion compensation using minus rounding. When the decoded image is other than a P frame, motion compensation is not performed, or only the motion compensation using plus rounding is performed.