Image decoding device, image decoding method, and program

An image decoding method comprising:

• determining whether or not an application condition of BDOF processing is satisfied for each block;
• and
• generating a prediction signal by executing the BDOF processing in a case where it is determined that the application condition is satisfied;
• wherein
• a condition on time distances between two reference frames and a target frame based on a weight coefficient in a case where calculation is performed using pixel values of the two reference frames or values calculated from the pixel values in the BDOF processing is set as the application condition, and
• a ratio between each of the two reference frames and the target frame in the time distances is determined so as to be proportional to a reciprocal of the weight coefficient.

A non-transitory computer readable medium with instructions thereon that when executed by a processor of an image decoding device, cause the processor to:

• determine whether or not an application condition of bi-directional optical flow (BDOF) processing is satisfied for each block, and
• generate a prediction signal by executing the BDOF processing in a case where it is determined that the application condition is satisfied, wherein
• a condition on time distances between two reference frames and a target frame based on a weight coefficient in a case where calculation is performed using pixel values of the two reference frames or values calculated from the pixel values in the BDOF processing is set as the application condition, and
• a ratio between each of the two reference frames and the target frame in the time distances is determined so as to be proportional to a reciprocal of the weight coefficient.