BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present document relates to an image coding technology, and more specifically, to a method and an apparatus for performing inter prediction based on a decoder-side motion vector refinement (DMVR).

Related Art

The demands for high-resolution and high-quality images and video, such as an ultra high definition (UHD) image and video of 4K or 8K or more, are recently increasing in various fields. As image and video data become high resolution and high quality, the amount of information or the number of bits that is relatively transmitted is increased compared to the existing image and video data. Accordingly, if image data is transmitted using a medium, such as the existing wired or wireless wideband line, or image and video data are stored using the existing storage medium, transmission costs and storage costs are increased.

Furthermore, interests and demands for immersive media, such as virtual reality (VR), artificial reality (AR) content or a hologram, are recently increasing. The broadcasting of an image and video having image characteristics different from those of real images, such as game images, is increasing.

Accordingly, there is a need for a high-efficiency image and video compression technology in order to effectively compress and transmit or store and playback information of high-resolution and high-quality images and video having such various characteristics.

SUMMARY

This disclosure provides a method and an apparatus for increasing image coding efficiency.

This disclosure also provides a method and an apparatus of an efficient inter prediction.

This disclosure also provides a method and an apparatus for performing an inter prediction based on a Decoder-side Motion Vector Refinement (DMVR).

This disclosure also provides a method and an apparatus for performing an inter prediction based on a Bi-directional optical flow (BDOF).

This disclosure also provides a method and an apparatus for enhancing prediction performance by providing a condition for determining whether to apply a DMVR for enhancing image coding efficiency and/or a condition for determining whether to apply a BDOF.

The exemplary embodiment of the present document provides an image decoding method performed by a decoding apparatus. The method includes deriving a motion vector of a current block, determining whether to apply refinement to the motion vector of the current block, deriving a refined motion vector by applying a decoder-side motion vector refinement (DMVR) to the motion vector, when determining to apply the refinement to the motion vector of the current block, deriving prediction samples for the current block based on the refined motion vector, and generating reconstructed samples for the current block based on the prediction samples, in which the determining of whether to apply the refinement determines whether to apply the refinement based on at least one of a size of the current block or bi-prediction weight index information of the current block.

Another exemplary embodiment of the present document provides an image encoding method performed by an image encoding apparatus. The method includes deriving a motion vector of a current block, determining whether to apply refinement to the motion vector of the current block, deriving a refined motion vector by applying a decoder-side motion vector refinement (DMVR) to the motion vector, when determining to apply the refinement to the motion vector of the current block, deriving prediction samples for the current block based on the refined motion vector, deriving residual samples based on the prediction samples, generating residual information based on the residual samples, and encoding image information including the residual information, in which the determining of whether to apply the refinement determines whether to apply the refinement based on at least one of a size of the current block or bi-prediction weight index information of the current block.

According to this disclosure, overall image/video compression efficiency can be increased.

According to this disclosure, calculation complexity can be reduced and overall coding efficiency can be enhanced through an efficient inter prediction.

According to this disclosure, various application conditions are proposed in applying a DMVR and/or BDOF of refining motion information during a motion compensation process to enhance efficiency in terms of complexity and performance.

