Prediction image generation method, image coding method, image decoding method, and prediction image generation apparatus

An image decoding method for decoding a current block in a first image using a coded bitstream, the image decoding method comprising:

• obtaining first data from the coded bitstream that indicates a previously determined number of a first plurality of points in a current block of the first image to be used to select motion information for each point of the first plurality of points in the current block in affine translation;
• selecting the motion information for each point of the first plurality of points in the current block by selecting a second plurality of points where each point of the second plurality of points corresponds to one of the first plurality of points, the second plurality of points being included in a second image different from the first image, and a number of selected motion information being equal to the number of the first plurality of points indicated by the first data;
• generating a prediction image to decode the current block of the first image based on the selected motion information in affine translation;
• and
• decoding the current block of the first image.

A non-transitory recording medium storing thereon a computer program, which when executed by a processor, causes the processor to perform operations, including:

• obtaining first data from a coded bitstream that indicates a previously determined number of a first plurality of points in a current block of a first image to be used to select motion information for each point of the first plurality of points in the current block in affine translation;
• selecting the motion information for each point of the first plurality of points in the current block by selecting a second plurality of points where each point of the second plurality of points corresponds to one of the first plurality of points, the second plurality of points being included in a second image different from the first image, and a number of selected motion information being equal to the number of the first plurality of points indicated by the first data;
• generating a prediction image to decode the current block of the first image based on the selected motion information in affine translation;
• and
• decoding the current block of the first image.