VIDEO DECODING METHOD USING RESIDUAL INFORMATION IN VIDEO CODING SYSTEM, AND APPARATUS THEREOF

1 . An image decoding method performed by a decoding apparatus, comprising:

receiving residual information for a current block;

deriving a context index increment for a sign flag of a current residual coefficient in a current sub-block of the current block;

decoding the sign flag based on the context index increment;

deriving the current residual coefficient based on the sign flag;

deriving a residual sample based on the current residual coefficient; and

generating a reconstructed picture based on the residual sample,

wherein it is determined whether the current block is a transform skip block, and

based on the current block being the transform skip block, sign flags of residual coefficients of the current block including the current residual coefficient are context-based decoded,

wherein the context index increment for the sign flag is derived based on a sign level of a residual coefficient prior to the current residual coefficient in the current sub-block,

wherein a value of the context index increment is derived as 0, based on the current residual coefficient being a first residual coefficient in scan order in the current sub-block.

2 . The image decoding method of claim 1 ,

wherein, when a value of the sign level of the residual coefficient prior to the current residual coefficient is 0, a value of the context index increment for the sign flag of the current residual coefficient is derived as 0,

wherein, when the value of the sign level of the residual coefficient prior to the current residual coefficient is 1, a value of the context index increment for the sign flag of the current residual coefficient is derived as 1.

3 . The image decoding method of claim 1 , wherein the context index increment for the sign flag is derived as one of a plurality of context index increments based on sign levels of a plurality of residual coefficients prior to the current residual coefficient in the current sub-block.

4 . An image encoding method performed by an encoding apparatus, comprising:

deriving a current residual coefficient in a current sub-block of a current block;

deriving a context index increment for a sign flag of the current residual coefficient;

encoding the sign flag based on the context index increment; and

generating a bitstream including the sign flag,

wherein it is determined whether the current block is a transform skip block, and

based on the current block being the transform skip block, sign flags of residual coefficients of the current block including the current residual coefficient are context-based encoded,

wherein the context index increment for the sign flag is derived based on a sign level of a residual coefficient prior to the current residual coefficient in the current sub-block,

wherein a value of the context index increment is determined as 0, based on the current residual coefficient being a first residual coefficient in scan order in the current sub-block.

5 . The image encoding method of claim 4 ,

wherein, when a value of the sign level of the residual coefficient prior to the current residual coefficient is 0, a value of the context index increment for the sign flag of the current residual coefficient is derived as 0,

wherein, when the value of the sign level of the residual coefficient prior to the current residual coefficient is 1, a value of the context index increment for the sign flag of the current residual coefficient is derived as 1.

6 . A computer-readable storage medium storing a bitstream generated by a method, the method comprising:

deriving a current residual coefficient in a current sub-block of a current block;

deriving a context index increment for a sign flag of the current residual coefficient;

encoding the sign flag based on the context index increment; and

generating the bitstream including the sign flag,

wherein it is determined whether the current block is a transform skip block, and based on the current block being the transform skip block, sign flags of residual coefficients of the current block including the current residual coefficient are context-based encoded,

wherein the context index increment for the sign flag is derived based on a sign level of a residual coefficient prior to the current residual coefficient in the current sub-block,

wherein a value of the context index increment is determined as 0, based on the current residual coefficient being a first residual coefficient in scan order in the current sub-block.

7 . A transmission method of data for image the method comprising:

obtaining a bitstream of image information including sign flag of a current residual coefficient in a current sub-block of a current block; and

transmitting the data including the bitstream of the image information including the sign flag,

wherein it is determined whether the current block is a transform skip block, and

based on the current block being the transform skip block, sign flags of residual coefficients of the current block including the current residual coefficient are context-based encoded,

wherein the sign flag is generated by deriving the current residual coefficient in the current sub-block of the current block, deriving a context index increment for the sign flag of the current residual coefficient, encoding the sign flag based on the context index increment, wherein the context index increment for the sign flag is derived based on a sign level of a residual coefficient prior to the current residual coefficient in the current sub-block,

wherein a value of the context index increment is determined as 0, based on the current residual coefficient being a first residual coefficient in scan order in the current sub-block.