Image coding method, image decoding method, image coding apparatus, image decoding apparatus, and image coding and decoding apparatus

An image coding apparatus, comprising:

• a divider configured to divide a picture into tiles;
• a coder configured to code the tiles to generate pieces of coded data each of which corresponds to a different one of the tiles;
• and
• a bitstream generator configured to generate a bitstream including the pieces of coded data,
• wherein the coder is configured to:
• generate a first code string by coding a first tile which is one of the tiles with reference to coding information of an already-coded tile neighboring the first tile when a boundary between the first tile and the already-coded tile is a first boundary, and coding the first tile without referring to the coding information of the already-coded tile when the boundary between the first tile and the already-coded tile is a second boundary;
• and
• add a bit string after the first code string to make a bit length of first coded data which is one of the pieces of coded data, a multiple of a predetermined N bits, N being an integer greater than or equal to 2, and
• the bitstream generator is configured to generate the bitstream including tile boundary independence information indicating whether each of boundaries between the tiles is one of the first boundary and the second boundary.