Image encoder and related non-transitory computer readable medium for image decoding

A decoder comprising:

• circuitry;
• and
• a memory coupled to the circuitry;
• wherein the circuitry, in operation, performs a partition process including:
• selecting, from a set of motion vector candidates, a first motion vector for a first partition in a current block;
• calculating first values of a set of pixels between the first partition and a second partition in the current block, using the first motion vector for the first partition;
• calculating second values of the set of pixels, using a second motion vector for the second partition;
• and
• calculating third values of the set of pixels by weighting the first values and the second values, and
• when a ratio of a width to a height of the current block is larger than 4 or a ratio of the height to the width of the current block is larger than 4, the circuitry disables the partition process.

A non-transitory computer readable medium storing a bitstream, the bitstream including information according to which a decoder performs a partition process, the information indicating a size of a current block,

• in the partition process:
• a first motion vector for a first partition in the current block being selected from a set of motion vector candidates;
• first values of a set of pixels between the first partition and a second partition in the current block being calculated using the first motion vector for the first partition;
• second values of the set of pixels being calculated using a second motion vector for the second partition;
• and
• third values of the set of pixels being calculated by weighting the first values and the second values, wherein
• when a ratio of a width to a height of the current block is larger than 4 or a ratio of the height to the width of the current block is larger than 4, the decoder disables the partition process.