Method for decoding video for residual coding and device therefor

An image encoding method performed by an encoding apparatus, the method comprising:

• deriving a prediction sample of a current block based on inter prediction or intra prediction;
• deriving a residual sample of the current block based on the prediction sample;
• deriving a current residual coefficient based on the residual sample;
• and
• encoding image information including prediction mode information representing a prediction mode of the current block and residual syntax elements for the current residual coefficient,
• wherein a number of context coded residual syntax elements for residual coefficients prior to the current residual coefficient among residual coefficients of the current block is equal to a maximum number of context coded bins of the current block,
• wherein the residual syntax elements for the current residual coefficient include coefficient level information for the current residual coefficient and a sign flag of the current residual coefficient,
• wherein the coefficient level information represents an absolute value of a coefficient level of the current residual coefficient, and the sign flag of the current residual coefficient represents a sign of the current residual coefficient,
• wherein the current residual coefficient is encoded without performing level mapping,
• wherein the residual coefficients prior to the current residual coefficient are encoded by performing the level mapping, and
• wherein the level mapping for a target residual coefficient comprises:
• deriving a maximum value among an absolute level of a left residual coefficient of the target residual coefficient and an absolute level of a top residual coefficient of the target residual coefficient,
• comparing an absolute level of the target residual coefficient with the maximum value, and
• deriving a modified absolute level of the target residual coefficient based on the comparison.

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

• deriving a prediction sample of a current block based on inter prediction or intra prediction;
• deriving a residual sample of the current block based on the prediction sample;
• deriving a current residual coefficient based on the residual sample;
• encoding image information including prediction mode information representing a prediction mode of the current block and residual syntax elements for the current residual coefficient;
• and
• generating the bitstream including the image information,
• wherein a number of context coded residual syntax elements for residual coefficients prior to the current residual coefficient among residual coefficients of the current block is equal to a maximum number of context coded bins of the current block,
• wherein the residual syntax elements for the current residual coefficient include coefficient level information for the current residual coefficient and a sign flag of the current residual coefficient,
• wherein the coefficient level information represents an absolute value of a coefficient level of the current residual coefficient, and the sign flag of the current residual coefficient represents a sign of the current residual coefficient,
• wherein the current residual coefficient is encoded without performing level mapping,
• wherein the residual coefficients prior to the current residual coefficient are encoded by performing the level mapping, and
• wherein the level mapping for a target residual coefficient comprises:
• deriving a maximum value among an absolute level of a left residual coefficient of the target residual coefficient and an absolute level of a top residual coefficient of the target residual coefficient,
• comparing an absolute level of the target residual coefficient with the maximum value, and
• deriving a modified absolute level of the target residual coefficient based on the comparison.

A transmission method of data for image, the method comprising:

• obtaining a bitstream of image information including prediction mode information representing a prediction mode of a current block and residual syntax elements for a current residual coefficient in the current block;
• and
• transmitting the data including the bitstream of the image information including the prediction mode information and the residual syntax elements,
• wherein a prediction sample of the current block is derived based on inter prediction or intra prediction, and the prediction mode information is information whether the inter prediction or the intra prediction is applied to the current block as the prediction mode of the current block,
• wherein the current residual coefficient is derived based on a residual sample of the current block and the residual sample is derived based on the prediction sample of the current block,
• wherein a number of context coded residual syntax elements for residual coefficients prior to the current residual coefficient among residual coefficients of the current block is equal to a maximum number of context coded bins of the current block,
• wherein the residual syntax elements for the current residual coefficient include coefficient level information for the current residual coefficient and a sign flag of the current residual coefficient,
• wherein the coefficient level information represents an absolute value of a coefficient level of the current residual coefficient, and the sign flag of the current residual coefficient represents a sign of the current residual coefficient,
• wherein the current residual coefficient is encoded without performing level mapping,
• wherein the residual coefficients prior to the current residual coefficient are encoded by performing the level mapping, and
• wherein the level mapping for a target residual coefficient comprises:
• deriving a maximum value among an absolute level of a left residual coefficient of the target residual coefficient and an absolute level of a top residual coefficient of the target residual coefficient,
• comparing an absolute level of the target residual coefficient with the maximum value, and
• deriving a modified absolute level of the target residual coefficient based on the comparison.