Image decoding method

An encoding apparatus which encodes an image on a block-by-block basis, the apparatus comprising:

• a division unit configured to divide a current block that is a unit of encoding into a plurality of sub-blocks each of which is a unit of prediction;
• a deriving unit configured to derive, for each of the plurality of sub-blocks, one or more prediction information candidates each of which is a candidate for prediction information indicating a reference picture list, a motion vector, and a reference picture index;
• a selecting unit configured to select a prediction information candidate to be used for encoding the current block from among the one or more prediction information candidates;
• an adding unit configured to add, to a bitstream, an index for identifying the selected prediction information candidate;
• and
• an encoding unit configured to encode the current block using the selected prediction information candidate,
• wherein the deriving unit is configured to:
• determine whether or not a neighboring block neighboring each of the plurality of sub-blocks is included in the current block, and when the neighboring block is not included in the current block, determine the neighboring block to be a reference block available to the sub-block, and when the neighboring block is included in the current block, determine the neighboring block not to be the reference block;
• and
• derive a prediction information candidate of the sub-block from prediction information of the reference block.

An encoding apparatus which encodes an image on a block-by-block basis, the apparatus comprising:

• storage;
• and
• processing circuitry that is coupled to the storage and executes the encoding, wherein the encoding includes:
• dividing a current block that is a unit of encoding into a plurality of sub-blocks each of which is a unit of prediction;
• deriving, for each of the plurality of sub-blocks, one or more prediction information candidates each of which is a candidate for prediction information indicating a reference picture list, a motion vector, and a reference picture index;
• selecting a prediction information candidate to be used for encoding the current block from among the one or more prediction information candidates;
• adding, to a bitstream, an index for identifying the selected prediction information candidate;
• and
• encoding the current block using the selected prediction information candidate,
• wherein the deriving includes:
• reading, from the storage, a neighboring block neighboring each of the plurality of sub-blocks;
• determining whether or not the neighboring block is included in the current block,
• when the neighboring block is not included in the current block, determining the neighboring block to be a reference block available to the sub-block, and when the neighboring block is included in the current block, determining the neighboring block not to be the reference block;
• and
• deriving a prediction information candidate of the sub-block from prediction information of the reference block.

A non-transitory computer readable medium storing a bitstream, the bitstream comprising information that causes a decoder to execute a decoding process for decoding, on a block-by-block basis, an image included in the bitstream, the decoding process comprising:

• dividing a current block that is a unit of decoding into a plurality of sub-blocks each of which is a unit of prediction;
• deriving, for each of the plurality of sub-blocks, one or more prediction information candidates each of which is a candidate for prediction information indicating a reference picture list, a motion vector, and a reference picture index;
• obtaining, from the bitstream, an index for selecting a prediction information candidate to be used for decoding the current block from among the one or more prediction information candidates;
• and
• decoding the current block using the prediction information candidate selected by the index,
• wherein the deriving includes:
• determining whether or not a neighboring block neighboring each of the plurality of sub-blocks is included in the current block, and when the neighboring block is not included in the current block, determining the neighboring block to be a reference block available to the sub-block, and when the neighboring block is included in the current block, determining the neighboring block not to be the reference block;
• and
• deriving a prediction information candidate of the sub-block from prediction information of the reference block.