Video coding apparatus and video coding method

A video coding apparatus that codes a current picture to generate a code string, the video coding apparatus comprising:

• a block practitioner which, in operation, divides the current picture into a plurality of blocks, the plurality of blocks including a first block and a second block;
• a residual coder which, in operation, generates a residual coefficient by calculating a difference between a prediction image which is generated for each of the plurality of blocks and the current picture;
• and
• a code string generator which, in operation, generates the code string based on the residual coefficient, wherein:
• the code string generator provides a common header information to both the first block and the second block, when a prediction information of the first block is the same as a prediction information of the second block, and
• the code string generator provides a prediction information of the first block as a header information of the first block to the first block and provides a prediction information of the second block as a header information of the second block to the second block, when the prediction information of the first block is different from the prediction information of the second block.

A decoding method for decoding an image, on a block-by-block basis, from a coded stream, the decoding method comprising:

• determining, for a first block, whether a common prediction information or a block prediction information is used for generating a prediction image for the first block;
• generating, when the first block is included in a group unit that is bigger than the first block, a prediction image corresponding to the first block using the common prediction information, the group unit including at least the first block and a second block, the common prediction information being used for all blocks included in the group unit;
• generating, when the first block is not included in the group unit, a prediction image corresponding to the first block using the block prediction information included in the first block;
• and
• generating a decoded image corresponding to the first block using the prediction image and a residual coefficient, the residual coefficient being included in the first block regardless of whether or not the first block is included in the group unit.

A decoding apparatus for decoding an image, on a block-by-block basis, from a coded stream, the decoding apparatus comprising:

• a processor;
• and
• a non-transitory memory having stored thereon executable instructions, which when executed, cause the processor to perform:
• reading a first information corresponding to a quantization parameter, the first information being used for a plurality of blocks included in a picture;
• determining, using a second information of a current picture including a current block and a third information of the current block included in the current picture, whether or not a fourth information corresponding to a quantization parameter of a current unit is used for the current block, the second information being an information on a picture-by-picture basis and the third information not being an information on a picture-by-picture basis;
• and
• decoding, when the fourth information is determined to be used for the current block, the current block by using the first information and the fourth information,
• wherein the fourth information is used for all of a plurality of blocks included in the current unit.