Picture coding device, picture coding method, and picture coding program, and picture decoding device, picture decoding method, and picture decoding program

A picture decoding method decoding a bitstream in which differential information between a picture that is a decoding target and a picture that is a prediction target is partitioned into a plurality of sub blocks, and the partitioned sub blocks are coded in a predetermined sequence, the picture decoding method comprising:

• decoding significant sub block information that represents whether or not all the values of differential coefficients belonging to the sub block are zero;
• decoding the value of the differential coefficient;
• and
• decoding significant differential coefficient information that represents whether or not the value of the differential coefficient is zero, and deriving an index based on the significant sub block information of a decoded sub block that is neighboring to the sub block that is a decoding target in the horizontal direction and the significant sub block information of a decoded sub block that is neighboring in the vertical direction, wherein the index is capable of distinguishing between four combinations of the significant sub block information of the decoded sub block that is neighboring in the horizontal direction and the significant sub block information of the decoded sub block that is neighboring in the vertical direction, and deriving a context used for decoding the significant differential coefficient information of the differential coefficient that is a decoding target based on the index and the position of the differential coefficient that is the decoding target in the sub block that is the decoding target,
• wherein deriving the context derives the context based on the vertical position of the differential coefficient that is the decoding target in the sub block that is the decoding target in a case where the significant sub block information of the decoded sub block that is neighboring in the horizontal direction is “1” and the significant sub block information of the decoded sub block that is neighboring in the vertical direction is “0”.

A non-transitory computer-readable recording medium having embodied thereon a picture decoding program decoding a bitstream in which differential information between a picture that is a decoding target and a picture that is a prediction target is partitioned into a plurality of sub blocks, and the partitioned sub blocks are coded in a predetermined sequence, the picture decoding program causing a computer to perform:

• decoding significant sub block information that represents whether or not all the values of differential coefficients belonging to the sub block are zero;
• decoding the value of the differential coefficient;
• and
• decoding significant differential coefficient information that represents whether or not the value of the differential coefficient is zero, and deriving an index based on the significant sub block information of a decoded sub block that is neighboring to the sub block that is a decoding target in the horizontal direction and the significant sub block information of a decoded sub block that is neighboring in the vertical direction, wherein the index is capable of distinguishing between four combinations of the significant sub block information of the decoded sub block that is neighboring in the horizontal direction and the significant sub block information of the decoded sub block that is neighboring in the vertical direction, and deriving a context used for decoding the significant differential coefficient information of the differential coefficient that is a decoding target based on the index and the position of the differential coefficient that is the decoding target in the sub block that is the decoding target,
• wherein deriving the context derives the context based on the vertical position of the differential coefficient that is the decoding target in the sub block that is the decoding target in a case where the significant sub block information of the decoded sub block that is neighboring in the horizontal direction is “1” and the significant sub block information of the decoded sub block that is neighboring in the vertical direction is “0”.