BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to an image coding technique, and more particularly, to an image decoding method in which a context model of a sign flag indicating a sign of a residual coefficient is derived in an image coding system and the sign flag is coded based on the derived context model, and an apparatus thereof.

Related Art

Recently, demand for high-resolution, high-quality images, such as High Definition (HD) images and Ultra High Definition (UHD) images, has been increasing in various fields. As the image data has high resolution and high quality, the amount of information or bits to be transmitted increases relative to the legacy image data. Therefore, when image data is transmitted using a medium such as a conventional wired/wireless broadband line or image data is stored using an existing storage medium, the transmission cost and the storage cost thereof are increased.

Accordingly, there is a need for a highly efficient image compression technique for effectively transmitting, storing, and reproducing information of high-resolution and high-quality images.

SUMMARY

The present disclosure provides a method and apparatus for improving image coding efficiency.

The present disclosure also provides a method and apparatus for improving residual coding efficiency.

The present disclosure also provides a method and apparatus for performing coding by deriving a context model of a sign flag indicating a sign of a residual coefficient, based on a sign flag of a previous residual coefficient coded prior to the residual coefficient, when residual information is coded.

According to an embodiment of the present disclosure, there is provided an image decoding method performed by a decoding apparatus. The method includes receiving residual information for a current block, deriving a context model 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 model, 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 the context model for the sign flag is derived based on a sign flag of a residual coefficient decoded prior to the current residual coefficient in the current sub-block.

According to another embodiment of the present disclosure, there is provided a decoding apparatus for performing image decoding. The decoding apparatus includes an entropy decoder for receiving residual information for a current block, deriving a context model 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 model, and deriving the current residual coefficient based on the sign flag, a transformer for deriving a residual sample based on the current residual coefficient, and an adder for generating a reconstructed picture based on the residual sample, wherein the context model for the sign flag is derived based on a sign flag of a residual coefficient decoded prior to the current residual coefficient in the current sub-block.

According to another embodiment of the present disclosure, there is provided an image encoding method performed by an encoding apparatus. The method includes deriving a current residual coefficient in a current sub-block of a current block, deriving a context model for a sign flag of the current residual coefficient, encoding the sign flag based on the context model, and generating a bitstream including the sign flag, wherein the context model for the sign flag is derived based on a sign flag of a residual coefficient encoded prior to the current residual coefficient in the current sub-block.

According to another embodiment of the present disclosure, there is provided a video encoding apparatus. The encoding apparatus includes a transformer for deriving a current residual coefficient in a current sub-block of a current block, and an encoder for deriving a context model for a sign flag of the current residual coefficient, encoding the sign flag based on the context model, and generating a bitstream including the sign flag, wherein the context model for the sign flag is derived based on a sign flag of a residual coefficient encoded prior to the current residual coefficient in the current sub-block.

According to the present disclosure, overall image/video compression efficiency can be improved.

According to the present disclosure, residual coding efficiency can be improved.

According to the present disclosure, a sign flag indicating a sign of a residual coefficient can be coded based on a context model, thereby saving an amount of bits assigned to the sign flag for the residual coefficient and improving overall residual coding efficiency.

According to the present disclosure, a context model for a sign flag indicating a sign of a residual coefficient is derived based on a sign flag of a residual coefficient coded prior to the residual coefficient, and thus the sign flag is coded by considering correlation between adjacent residual coefficients, thereby saving an amount of bits assigned to the sign flag and improving overall residual coding efficiency.

