Image encoding/decoding method and device, 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;

determining whether intra sub-partitions (ISP) is available for the current block based on the prediction mode of the current block being an intra prediction mode;

decoding ISP mode information for the current block, based on the ISP being available for the current block; and

generating a prediction sample for the current block based on the ISP mode information,

wherein the ISP mode information includes whether the current block is partitioned into sub-partitions.

2. The image decoding method of claim 1 , wherein the determining whether the ISP is available for the current block is performed based on comparison between a size of a luma component block of the current block and a predetermined threshold.

3. The image decoding method of claim 2 , wherein the predetermined threshold is a maximum transform size.

4. The image decoding method of claim 2 , wherein, when both a width and height of the luma component block of the current block are equal to or less than a predetermined threshold, it is determined that the ISP is available for the current block.

5. The image decoding method of claim 1 , wherein the generating the prediction sample for the current block based on the ISP mode information comprises:

generating a prediction sample for a luma component block by applying the ISP to the luma component block of the current block;

determining whether to apply the ISP to a chroma component block of the current block; and

generating a prediction sample for the chroma component block by applying the ISP to the chroma component block, upon determining that the ISP applies to the chroma component block of the current block.

6. The image decoding method of claim 5 , wherein the determining whether to apply the ISP to the chroma component block of the current block is performed based on at least one of a size of the chroma component block or a chroma format of the current block.

7. The image decoding method of claim 6 , wherein, when the chroma format of the current block is 4:2:2 or 4:4:4 and at least one of a width or height of the chroma component block is greater than a maximum transform size, it is determined that the ISP applies to the chroma component block of the current block.

8. The image decoding method of claim 5 , wherein, when the ISP applies to the chroma component block, a split direction and a number of sub-partitions for the chroma component block are determined based on a split direction and a number of sub-partitions for the luma component block.

9. The image decoding method of claim 8 , wherein the split direction and the number of sub-partitions for the chroma component block are equal to the split direction and the number of sub-partitions for the luma component block, respectively.

10. The image decoding method of claim 1 , wherein the generating the prediction sample for the current block based on the ISP mode information comprises:

generating a prediction sample for a luma component block by applying the ISP to the luma component block of the current block; and

generating a prediction sample for a chroma component block by applying the ISP to the chroma component block of the current block.

11. The image decoding method of claim 10 , wherein a split direction and a number of sub-partitions for the chroma component block are determined based on a split direction and a number of sub-partitions for the luma component block.

12. The image decoding method of claim 11 , wherein the split direction and the number of sub-partitions for the chroma component block are equal to the split direction and (the number of sub-partitions/2) of the luma component block, respectively.

13. 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;

determine whether intra sub-partitions (ISP) is available for the current block based on the prediction mode of the current block being an intra prediction mode;

decode ISP mode information for the current block, based on the ISP being available for the current block; and

generate a prediction sample for the current block based on the ISP mode information,

wherein the ISP mode information includes whether the current block is partitioned into sub-partitions.

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

determining a prediction mode of a current block;

determining whether intra sub-partitions (ISP) is available for the current block based on the prediction mode of the current block being an intra prediction mode;

determining whether to apply the ISP to the current block, based on the ISP being available for the current block;

generating a prediction sample for the current block by applying the ISP to the current block, based on the ISP being determined to be applied to the current block; and

encoding prediction mode information of the current block and ISP mode information,

wherein the ISP mode information includes whether the current block is partitioned into sub-partitions.

15. A method of transmitting a bitstream generated by the image encoding method of claim 14 , comprising:

transmitting the bitstream including the encoded prediction mode information and the encoded ISP mode information.