Image decoding method, image encoding method, image decoding apparatus, and image encoding apparatus

An image encoding method comprising:

• partitioning a picture into a plurality of tiles;
• encoding constraint tile information in a sequence header of a bitstream, the constraint tile information indicating a prohibition of reference from a current tile, which is one of the plurality of tiles, to another tile when the current tile is prohibited from referring to the another tile;
• generating a prediction motion vector list that includes a plurality of prediction motion vector candidates and a plurality of prediction motion vector indices respectively corresponding to the plurality of prediction motion vector candidates;
• selecting a prediction motion vector candidate from among the plurality of prediction motion vector candidates;
• encoding a current block included in the current tile by using the selected prediction motion vector candidate and encoding a prediction motion vector index for specifying the selected prediction motion vector candidate in the prediction motion vector list, and
• wherein when (i) the current tile is prohibited from referring to the another tile and (ii) the current block is located at an end of the current tile, in the generating the prediction motion vector list, the prediction motion vector list not including any temporal motion vectors, each of which refers to another pictures which is different from a current picture in which the current block is included, is generated, and
• in the encoding of the constraint tile information, a temporal motion vector prohibition flag that indicates prohibition to use a temporal motion vector in the current block, which is located at right end of the current tile, is encoded.