Image decoding method of decoding a current picture with prediction using one or both of a first reference picture list and a second reference picture list

A computer-implemented image decoding method of decoding a current picture per block with prediction using one or both of (i) a first reference picture list including a first current reference picture for a current block, the first current reference picture being referred to by a first current motion vector and (ii) a second reference picture list, the image decoding method comprising:

• judging whether or not a second current reference picture for the current block is identical to a second adjacent reference picture for an adjacent block adjacent to the current block, the second current reference picture being (i) included in the second reference picture list and (ii) referred to by a second current motion vector, and the second adjacent reference picture being (i) included in a second adjacent reference picture list and (ii) referred to by a second adjacent motion vector;
• when the second current reference picture is judged to be identical to the second adjacent reference picture, adding the second adjacent motion vector to a candidate list for the second current motion vector;
• only when the second current reference picture is judged to not be identical to the second adjacent reference picture, (A) judging whether or not the second current reference picture is identical to a first adjacent reference picture for the adjacent block, the first adjacent reference picture being (i) included in a first adjacent reference picture list and (ii) referred to by the first adjacent motion vector, and (B) when the second current reference picture is judged to be identical to the first adjacent reference picture, adding the first adjacent motion vector to the candidate list for the second current motion vector;
• selecting a predicted motion vector to be used for decoding the second current motion vector from the candidate list for second current motion vector;
• and
• decoding the second current motion vector using the selected predicted motion vector,
• wherein when the second current reference picture is judged to not be identical to the first adjacent reference picture, the first adjacent motion vector is not added to the candidate list for the second current motion vector.

An image decoding apparatus of decoding a current picture per block with prediction using one or both of a first reference picture list and a second reference picture list, the image decoding apparatus comprising:

• a processor;
• and
• a non-transitory memory storing thereon a program, which when executed by the processor, causes the processor to:
• judge whether or not a second current reference picture for the current block is identical to a second adjacent reference picture for an adjacent block adjacent to the current block, the second current reference picture being (i) included in the second reference picture list and (ii) referred to by a second current motion vector, and the second adjacent reference picture being (i) included in a second adjacent reference picture list and (ii) referred to by a second adjacent motion vector;
• when the second current reference picture is judged to be identical to the second adjacent reference picture, add the second adjacent motion vector to a candidate list for the second current motion vector;
• only when the second current reference picture is judged to not be identical to the second adjacent reference picture, (A) judge whether or not the second current reference picture is identical to a first adjacent reference picture for the adjacent block, the first adjacent reference picture being (i) included in a first adjacent reference picture list and (ii) referred to by the first adjacent motion vector, and (B) when the second current reference picture is judged to be identical to the first adjacent reference picture, add the first adjacent motion vector to the candidate list for the second current motion vector;
• select a predicted motion vector to be used for decoding the second current motion vector from the candidate list for second current motion vector;
• and
• decode the second current motion vector using the selected predicted motion vector,
• wherein when the second current reference picture is judged to not be identical to the first adjacent reference picture, the first adjacent motion vector is not added to the candidate list for the second current motion vector.