Image information encoding method and encoder, and image information decoding method and decoder

A motion compensation apparatus comprising:

• receiving means for receiving mode information that identify a field motion estimate/compensate mode;
• motion compensation means for performing, on the basis of the mode information, a motion compensation of a decoded image signal including a luma signal and a chroma signal in a format in which the number of chroma pixels is vertically different from the number of luma pixels;
• detecting means for detecting a condition that a reference field has a different parity from a current field for a motion compensation;
• and
• controlling means for controlling, in the detected condition, the motion compensation so as to vertically shift a phase of the chroma signal in the reference field so that the reference field will coincide in phase of the chroma signal with a current field.

A motion compensation apparatus comprising:

• a receiving unit configured to receive mode information that identify a field motion estimate/compensate mode;
• a motion estimation unit configured to perform, on the basis of the mode information, a motion compensation of a decoded image signal including a luma signal and a chroma signal in a format in which the number of chroma pixels is vertically different from the number of luma pixels;
• a detecting unit configured to detect means for detecting a condition that a reference field has a different parity from a current field for a motion compensation;
• and
• a controlling unit configured to control, in the detected condition, the motion compensation so as to vertically shift a phase of the chroma signal in the reference field so that the reference field will coincide in phase of the chroma signal with a current field.