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

A decoding apparatus which decodes last position information indicating a horizontal position and a vertical position of a last non-zero coefficient in a predetermined order within a current block to be decoded, the current block being included in a picture and including a plurality of coefficients, the decoding apparatus comprising:

• electrical processing circuitry;
• and
• storage coupled to the electrical processing circuitry;
• wherein the electrical processing circuitry, which includes one or more processors and one or more integrated circuits, is configured to perform the following using the storage:
• obtaining a bitstream including a first partial signal, a second partial signal, a third partial signal, and a fourth partial signal, in this order;
• performing first arithmetic decoding on the first partial signal and the third second partial signal respectively to obtain a decoded first partial signal and a decoded third second partial signal;
• generating a first flag that indicates when the decoded first partial signal is greater than or equal to a predetermined value;
• generating a second flag that indicates when the decoded second partial signal is greater than or equal to the predetermined value;
• when the first flag is generated, performing second arithmetic decoding on the second third partial signal and when the second flag is generated, performing second arithmetic decoding on the fourth partial signal, respectively, to obtain a decoded second third partial signal and a decoded fourth partial signal, the second arithmetic decoding being different from the first arithmetic decoding;
• deriving a horizontal component of the last position information indicating the horizontal position of the non-zero coefficient from the decoded first partial signal and the decoded third partial signal;
• and
• deriving a vertical component of the last position information indicating the vertical position of the non-zero coefficient from the decoded second partial signal and the decoded fourth partial signal.

A decoding apparatus which decodes last position information indicating a horizontal position and a vertical position of a last non-zero coefficient in a predetermined order within a current block to be decoded, the current block being included in a picture and including a plurality of coefficients, the decoding apparatus comprising:

• an obtainer configured to obtain a bitstream including a first partial signal, a second partial signal, a third partial signal, and a fourth partial signal, in this order;
• an arithmetic decoder configured to:
• perform a first arithmetic decoding on the first partial signal and the third second partial signal respectively to obtain a decoded first partial signal and a decoded third second partial signal;
• and
• generate a first flag that indicates when the decoded first partial signal is greater than or equal to a predetermined value;
• generate a second flag that indicates when the decoded second partial signal is greater than or equal to the predetermined value;
• when the first flag is generated, perform a second arithmetic decoding on the second third partial signal and when the second flag is generated, perform second arithmetic decoding on the fourth partial signal respectively to obtain a decoded second third partial signal and a decoded fourth partial signal, the second arithmetic decoding being different from the first arithmetic decoding;
• and
• a deriver configured to:
• derive a horizontal component of the last non-zero coefficient indicting the horizontal position of the non-zero coefficient from the decoded first partial signal and the decoded third partial signal;
• and
• derive a vertical component of the last non-zero coefficient indicting the vertical position of the non-zero coefficient from the decoded second partial signal and the decoded fourth partial signal.