Image encoding and decoding of chroma block using luma block

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.

A non-transitory computer-readable storage medium storing a bitstream, the bitstream being encoded by 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.