Patent ID: 9681130
Date: 2017-06-13
CPC Classifications: H04N

Claim:
1. A method for decoding 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 method comprising: obtaining a code string, the code string being arranged to include, in this order, (i) first prefix data of a horizontal component of the difference motion vector, (ii) second prefix data of a vertical component of the difference motion vector, (iii) first suffix data of the horizontal component of the difference motion vector, and (iv) second suffix data of the vertical component of the difference motion vector; performing context adapted binary arithmetic decoding on first grouped data that includes (i) the first prefix data of the horizontal component of the difference motion vector and (ii) the second prefix data of the vertical component of the difference motion vector, the context adapted binary arithmetic decoding being performed by using a variable probability; performing bypass decoding on 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, the bypass decoding being performed using a fixed probability, and the bypass decoding being performed on the second grouped data subsequent to the context adapted binary arithmetic decoding performed on the first grouped data; and deriving the horizontal component of the difference motion vector from a combination of the first prefix data and the first suffix data, and deriving the vertical component of the difference motion vector from a combination of the second prefix data and the second suffix data wherein the first prefix data includes a first portion indicating whether or not the horizontal component of the difference motion vector is 0, and a second portion different from the first portion, the second prefix data includes a third portion indicating whether or not the vertical component of the difference motion vector is 0, and a fourth portion different from the third portion, when the first portion indicates that the horizontal component of the difference motion vector is 0, (i) the context adapted binary arithmetic decoding is not performed on the second portion and (ii) the bypass decoding is not performed on the first suffix data, when the first portion indicates that the horizontal component of the difference motion vector is not 0, the context adapted binary arithmetic decoding is performed on the second portion, when the third portion indicates that the vertical component of the difference motion vector is 0, (i) the context adapted binary arithmetic decoding is not performed on the fourth portion and (ii) the bypass decoding is not performed on the second suffix data, and when the third portion indicates that the vertical component of the difference motion vector is not 0, the context adapted binary arithmetic decoding is performed on the fourth portion.