BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to an image coding technology, and more specifically, a method and an apparatus for predicting a temporal motion vector in units of a sub-block in an image coding system.

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

An object of the present disclosure is to provide a method and an apparatus for enhancing image coding efficiency.

Another object of the present disclosure is to provide an efficient inter-prediction method and apparatus.

Still another object of the present disclosure is to provide a method and an apparatus for deriving a sub-block-based temporal motion vector, thereby improving the prediction performance.

Yet another object of the present disclosure is to provide a method and an apparatus for adjusting the size of a sub-block when deriving a sub-block-based temporal motion vector, thereby reducing the loss of the compression performance compared to the improvement in the complexity of a hardware.

An exemplary embodiment of the present disclosure provides an image decoding method performed by a decoding apparatus. The method includes: determining whether to use an advanced temporal motion vector predictor (ATMVP) candidate in units of sub-block for a current block, specifying a corresponding block corresponding to the current block in a reference picture based on a motion vector for a spatial neighboring block of the current block, if the ATMVP candidate in units of sub-block is used, deriving the ATMVP candidate in units of sub-block for the current block based on the motion vectors in units of sub-block of the corresponding block, configuring a merge candidate list including the ATMVP candidate in units of sub-block for the current block, generating prediction samples of the current block by deriving the motion vectors in units of sub-block for the current block based on the merge candidate list, and reconstructing a current picture based on the prediction samples of the current block.

Another exemplary embodiment of the present disclosure provides an image encoding method performed by an encoding apparatus. The method includes: determining whether to use an advanced temporal motion vector predictor (ATMVP) candidate in units of sub-block for a current block, specifying a corresponding block corresponding to the current block in a reference picture based on a motion vector for a spatial neighboring block of the current block, if the ATMVP candidate in units of sub-block is used, deriving the ATMVP candidate in units of sub-block for the current block based on the motion vectors in units of sub-block of the corresponding block, configuring a merge candidate list including the ATMVP candidate in units of sub-block for the current block, generating a candidate index indicating a candidate applied to the current block among the candidates within the merge candidate list, and encoding image information including the candidate index to output the encoded image information as a bitstream.

The present disclosure may enhance the overall image/video compression efficiency.

The present disclosure may enhance the efficiency of the image coding based on the inter-prediction, and reduce an amount of data necessary for transmitting the residual signal through the efficient inter-prediction.

The present disclosure may efficiently induce the temporal motion vector information in units of sub-block according to the size of the current block, thereby improving the performance and efficiency of the inter-prediction.

