Method and apparatus for video encoding/decoding using IBC mode, and method for transmitting bitstream

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

determining a prediction mode of a current block based on prediction mode information of the current block obtained from a bitstream;

obtaining a transform coefficient block of the current block from the bitstream;

dequantizing the transform coefficient block to generate a dequantized transform coefficient block;

determining a transform kernel for the dequantized transform coefficient block; and

generating a residual block of the current block by performing inverse transform on the dequantized transform coefficient block using the transform kernel,

wherein the transform kernel is determined based on transform, kernel index information obtained from the bitstream,

wherein, based on that the prediction mode of the current block is an inter prediction mode or an intra prediction mode, the transform kernel index information is obtained from the bitstream based on predetermined flag information specifying whether explicit signaling is performed, and

wherein, based on that the prediction mode of the current block is an intra block copy (IBC) mode which refers to a block located in a same picture as the current block and decoded before the current block, the transform kernel index information is not obtained from the bitstream regardless of the predetermined flag information.

2. The image decoding method of claim 1 ,

wherein, based on that the prediction mode of the current block is neither the inter prediction mode nor the intra prediction mode, the transform kernel index information is not obtained from the bitstream and is derived as a predetermined value.

3. The image decoding method of claim 1 ,

wherein, based on that the prediction mode of the current block is the IBC mode, the transform kernel index information is determined as a value specifying a predetermined first transform kernel.

4. The image decoding method of claim 3 ,

wherein the first transform kernel is either DCT2 or DCT7.

5. The image decoding method of claim 1 ,

wherein the determining the transform kernel for the dequantized transform coefficient block comprises deriving the transform kernel of the current block, based on first flag information specifying whether the transform kernel index information for a block encoded in the intra prediction mode is able to be included in the bitstream and second flag information specifying whether the transform kernel index information for a block encoded in the inter prediction mode is able to be included in the bitstream, and

wherein the first flag information and the second flag information are obtained from the bitstream.

6. The image decoding method of claim 5 ,

wherein, based on that both the first flag information and the second flag information have a first value specifying that the transform kernel index information is not included in the bitstream and the prediction mode of the current block is the IBC mode, the transform kernel of the current block is derived based on a width and a height of the current block.

7. The image decoding method of claim 6 ,

wherein the transform kernel of the current block includes a horizontal transform kernel and a vertical transform kernel,

wherein the horizontal transform kernel of the current block is determined based on whether the width of the current block is within a predetermined range and comparison between the width and the height of the current block, and

wherein the vertical transform kernel of the current block is determined based on whether the height of the current block is within a predetermined range and comparison between the width and the height of the current block.

8. The image decoding method of claim 5 ,

wherein, based on that at least one of the first flag information and the second flag information has a second value specifying that the transform kernel index information is able to be included in the bitstream and the prediction mode of the current block is the IBC mode,

the transform kernel of the current block is derived based on the transform kernel index information, and

the transform kernel index information is not obtained from the bitstream and is derived as a predetermined value.

9. The image decoding method of claim 1 ,

wherein, based on that the transform kernel index information is not obtained from the bitstream, the transform kernel index information is derived as a predetermined value,

wherein, based on that the prediction mode of the current block is the IBC mode, the transform kernel index information is derived as a first value, and

wherein, based on that the prediction mode of the current block is a prediction mode other than the IBC mode, the transform kernel index information is derived as a second value different from the first value.

10. An image decoding apparatus, comprising:

a memory; and

at least one processor,

wherein the at least one processor is configured to:

determine a prediction mode of a current block based on prediction mode information of the current block obtained from a bitstream,

obtain a transform coefficient block of the current block from the bitstream,

dequantize the transform coefficient block to generate a dequantized transform coefficient block,

determine a transform kernel for the dequantized transform coefficient block, and

generate a residual block of the current block by performing inverse transform on the dequantized transform coefficient block using the transform kernel,

wherein the transform kernel is determined based on transform kernel index information obtained from the bitstream,

wherein, based on that the prediction mode of the current block is an inter prediction mode or an intra prediction mode, the transform kernel index information is obtained from the bitstream based on predetermined flag information specifying whether explicit signaling is performed, and

wherein, based on that the prediction mode of the current block is an intra block copy (IBC) mode which refers to a block located in a same picture as the current block and decoded before the current block, the transform kernel index information is not obtained from the bitstream regardless of the predetermined flag information.

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

selecting a prediction mode of a current block;

generating a prediction block for the current block based on the selected prediction mode;

generating a residual block for the current block based on the prediction block;

selecting a transform kernel for transforming the residual block based on the prediction mode;

transforming the residual block based on the transform kernel to generate a transform coefficient block;

quantizing the transform coefficient block to generate a quantized transform coefficient block; and

encoding the quantized transform coefficient block to generate a bitstream,

wherein, based on that the prediction mode of the current block is an inter prediction mode or an intra prediction mode, transform kernel index information of the transform kernel is encoded into the bitstream based on predetermined flag information specifying whether explicit signaling is performed, and

wherein, based on that the prediction mode of the current block is an intra block copy (IBC) mode which refers to a block located in a same picture as the current block and encoded before the current block, the transform kernel index information is not encoded into the bitstream regardless of the predetermined flag information.

12. The image encoding method of claim 11 ,

wherein, based on that the prediction mode of the current block is the IBC mode,

the transforming the residual block is performed based on a predetermined transform kernel, and

transform kernel index information of the predetermined transform kernel used for the transforming the residual block is not included in the bitstream.

13. The image encoding method of claim 11 ,

wherein first flag information specifying whether the transform kernel index information for a block encoded in the intra prediction mode is able to be included in the bitstream and second flag information specifying whether the transform kernel index information for a block encoded in the inter prediction mode is able to be included in the bitstream are included in the bitstream,

wherein, based on that at least one of the first flag information and the second flag information has a second value specifying that the transform kernel index information is able to be included in the bitstream and the prediction mode of the current block is an intra block copy (IBC) mode,

the transforming the residual block is performed based on a predetermined transform kernel, and

transform kernel index information of the predetermined transform kernel used for the transforming the residual block is not included in the bitstream.

14. The image encoding method of claim 13 ,

wherein, based on that both the first flag information and the second flag information have a first value specifying that the transform kernel index information is not included in the bitstream and the prediction mode of the current block is the IBC mode,

the transforming the residual block is performed based on a predetermined transform kernel,

the predetermined transform kernel is derived based on a width and a height of the current block, and

transform kernel index information of the predetermined transform kernel used for the transforming the residual block is not included in the bitstream.

15. A method of transmitting a bitstream comprising:

selecting a prediction mode of a current block;

generating a prediction block for the current block based on the selected prediction mode;

generating a residual block for the current block based on the prediction block;

selecting a transform kernel for transforming the residual block based on the prediction mode;

transforming the residual block based on the transform kernel to generate a transform coefficient block;

quantizing the transform coefficient block to generate a quantized transform coefficient block; and

encoding the quantized transform coefficient block to generate the bitstream; transmitting the bitstream,

wherein, based on that the prediction mode of the current block is an inter prediction mode or an intra prediction mode, transform kernel index information of the transform kernel is encoded into the bitstream based on predetermined flag information specifying whether explicit signaling is performed, and

wherein, based on that the prediction mode of the current block is an intra block copy (IBC) mode which refers to a block located in the same picture as the current block and encoded before the current block, the transform kernel index information is not encoded into the bitstream regardless of the predetermined flag information.