Method and apparatus for image encoding, and method and apparatus for image decoding

An image decoding apparatus comprising at least one processor configured to:

• obtain a first motion vector for a first N×N luma sub-block in a coding unit;
• obtain a second motion vector for a second N×N luma sub-block in the coding unit, wherein the second N×N luma sub-block is on the right side of the first N×N luma sub-block;
• determine a chroma motion vector using an averaged motion vector determined by averaging the first motion vector and the second motion vector;
• obtain predicted samples for a N×N chroma sub-block, using the chroma motion vector and a reference picture, wherein the N×N chroma sub-block includes a first N/2×N chroma sub-block corresponding to the first N×N luma sub-block and a second N/2×N chroma sub-block corresponding to the second N×N luma sub-block,
• wherein a chroma sub-sampling format of the image is 4:2:2.

An image encoding method comprising:

• obtaining a first motion vector for a first N×N luma sub-block in a coding unit;
• obtaining a second motion vector for a second N×N luma sub-block in the coding unit, wherein the second N×N luma sub-block is on the right side of the first N×N luma sub-block;
• determining a chroma motion vector using an averaged motion vector determined by averaging the first motion vector and the second motion vector;
• obtaining predicted samples for a N×N chroma sub-block, using the chroma motion vector and a reference picture, wherein the N×N chroma sub-block includes a first N/2×N chroma sub-block corresponding to the first N×N luma sub-block and a second N/2×N chroma sub-block corresponding to the second N×N luma sub-block, wherein a chroma sub-sampling format of the image is 4:2:2.