Image coding method for decoding a difference motion vector from a bitstream

An apparatus which decodes, from a bitstream, a difference motion vector which indicates a difference between a motion vector used to predict a picture and a predicted motion vector that is a prediction of the motion vector, the apparatus comprising:

• processing circuitry;
• and
• storage accessible from the processing circuitry,
• wherein, using the storage, the processing circuitry is adapted to:
• decode a first flag and a second flag by performing context adaptive binary arithmetic decoding with variable probability;
• decode, subsequent to decoding the first flag and the second flag, first grouped data that includes (i) a first prefix data of a horizontal component of the difference motion vector, (ii) a second prefix data of a vertical component of the difference motion vector;
• determine whether each of the horizontal component and the vertical component is greater than or equal to a predetermined value based on the decoded first grouped data;
• and
• decode, subsequent to decoding the first grouped data, second grouped data that includes (i) the first suffix data of the horizontal component of the difference motion vector, and (ii) the second suffix data of the vertical component of the difference motion vector if each of the horizontal component and the vertical component is determined to be greater than or equal to a predetermined value and skipping decoding the first suffix data when the horizontal component is less than the predetermined value and skipping decoding the second suffix data when the vertical component is less than the predetermined value;
• derive the horizontal component of the difference motion vector from the first prefix data in combination with any decoded first suffix data;
• and
• derive the vertical component of the difference motion vector from the second prefix data in combination with any decoded second suffix data;
• and
• wherein decoding the first prefix data, the second prefix data, and the second grouped data is performed in response to the first flag indicating that the horizontal component of the difference motion vector is not zero and the second flag indicating that the vertical component of the difference motion vector is not zero.

An apparatus which decodes, from a bitstream, a difference motion vector which indicates a difference between a motion vector used to predict a picture and a predicted motion vector that is a prediction of the motion vector, the apparatus comprising:

• processing circuitry;
• and
• storage accessible from the processing circuitry,
• wherein using the storage, the processing circuitry is adapted to:
• decode the first flag and the second flag by performing context adaptive binary arithmetic decoding with variable probability;
• decode, subsequent to decoding the first flag and the second flag, first grouped data that includes (i) a first prefix data of a horizontal component of the difference motion vector, (ii) a second prefix data of a vertical component of the difference motion vector;
• decode, subsequent to decoding the first grouped data, second grouped data that includes (i) the first suffix data of the horizontal component of the difference motion vector, and (ii) the second suffix data of the vertical component of the difference motion vector;
• derive the horizontal component of the difference motion vector from a combination of the first prefix data and the first suffix data;
• and
• derive the vertical component of the difference motion vector from a combination of the second prefix data and the second suffix data:,
• wherein decoding the first prefix data, the second prefix data, and the second grouped data is performed in response to the first flag indicating that the horizontal component of the difference motion vector is not zero and the second flag indicating that the vertical component of the difference motion vector is not zero.