Intra prediction method and device based on intra sub-partitions in image coding system

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

receiving prediction mode information for a current block;

receiving intra sub-partition (ISP) related information for the current block based on a size of the current block and a maximum transform block size;

deriving an intra prediction mode of the current block based on the prediction mode information; and

generating a prediction sample of the current block based on the intra prediction mode and the ISP related information,

wherein the ISP related information includes information on whether ISP is applied to the current block,

wherein, the ISP related information is received based on the following condition related to the size of the current block being satisfied,

cbWidth<=MaxTbSizeY && cbHeight<=MaxTbSizeY

wherein, the cbWidth represents a width of the current block, the cbHeight represents a height of the current block, and the MaxTbSizeY represents the maximum transform block size,

wherein, based on the width of the current block being greater than the maximum transform block size and the height of the current block being less than or equal to the maximum transform block size, the ISP related information is not received, and

wherein, based on the height of the current block being greater than the maximum transform block size and the width of the current block being less than or equal to the maximum transform block size, the ISP related information is not received.

2. The image decoding method of claim 1 , wherein, based on the information on whether the ISP is applied, indicating that the ISP is applied to the current block, the ISP related information further includes information on a split direction.

3. The image decoding method of claim 2 , wherein the information on whether the ISP is applied includes an intra_subpartitions_mode_flag field, and a value of the intra_subpartitions_mode_flag field is 0 or 1, and

wherein the information on the split direction includes an intra_subpartitions_split_flag field, and a value of the intra_subpartitions_split_flag field is 0 or 1.

4. The image decoding method of claim 2 , wherein the prediction sample is generated based on the intra prediction mode and sub-partitions of the current block, and

wherein the sub-partitions of the current block are derived based on the information on the split direction.

5. The image decoding method of claim 4 , wherein the sub-partitions of the current block include a first sub-partition and a second sub-partition,

wherein the prediction sample includes a prediction sample of the first sub-partition and a prediction sample of the second sub-partition,

wherein the prediction sample of the first sub-partition is generated based on the intra prediction mode and neighboring samples of the first sub-partition, and

wherein the prediction sample of the second sub-partition is generated based on the intra prediction mode and the prediction sample of the first sub-partition.

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

deriving an intra prediction mode of a current block;

deriving intra sub-partitions (ISP) related information for the current block based on a size of the current block and a maximum transform block size;

generating a prediction sample of the current block based on the intra prediction mode and the ISP related information;

generating a residual sample based on the prediction sample; and

encoding image information including prediction mode information on the intra prediction mode, the ISP related information and information on the residual sample,

wherein the ISP related information includes information on whether ISP is applied to the current block,

wherein, the ISP related information is derived based on the following condition related to the size of the current block being satisfied,

cbWidth<=MaxTbSizeY && cbHeight<=MaxTbSizeY

wherein, the cbWidth represents a width of the current block, the cbHeight represents a height of the current block, and the MaxTbSizeY represents the maximum transform block size,

wherein, based on the width of the current block being greater than the maximum transform block size and the height of the current block being less than or equal to the maximum transform block size, the ISP related information is not derived, and

wherein, based on the height of the current block being greater than the maximum transform block size and the width of the current block being less than or equal to the maximum transform block size, the ISP related information is not derived.

7. The image encoding method of claim 6 , wherein, based on the information on whether the ISP is applied, indicating that the ISP is applied to the current block, the ISP related information further includes information on a split direction.

8. The image encoding method of claim 7 , wherein the information on whether the ISP is applied includes an intra_subpartitions_mode_flag field, and a value of the intra_subpartitions_mode_flag field is 0 or 1, and

wherein the information on the split direction includes an intra_subpartitions_split_flag field, and a value of the intra_subpartitions_split_flag field is 0 or 1.

9. The image encoding method of claim 7 , wherein the prediction sample is generated based on the intra prediction mode and sub-partitions of the current block, and

wherein the sub-partitions of the current block are derived based on the information on the split direction.

10. The image encoding method of claim 9 , wherein the sub-partitions of the current block include a first sub-partition and a second sub-partition,

wherein the prediction sample includes a prediction sample of the first sub-partition and a prediction sample of the second sub-partition,

wherein the prediction sample of the first sub-partition is generated based on the intra prediction mode and neighboring samples of the first sub-partition, and

wherein the prediction sample of the second sub-partition is generated based on the intra prediction mode and the prediction sample of the first sub-partition.

11. A non-transitory computer-readable digital storage medium storing a bitstream generated by a method, the method comprising: performing deriving an intra prediction mode of a current block, deriving intra sub-partitions (ISP) related information for the current block based on a size of the current block and a maximum transform block size, generating a prediction sample of the current block based on the intra prediction mode and the ISP related information, generating a residual sample based on the prediction sample, and generating the bitstream by encoding image information including prediction mode information on the intra prediction mode, the ISP related information and information on the residual sample,

wherein the ISP related information includes information on whether ISP is applied to the current block,

wherein, the ISP related information is derived based on the following condition related to the size of the current block being satisfied,

cbWidth<=MaxTbSizeY && cbHeight<=MaxTbSizeY

wherein, the cbWidth represents a width of the current block, the cbHeight represents a height of the current block, and the MaxTbSizeY represents the maximum transform block size,

wherein, based on the width of the current block being greater than the maximum transform block size and the height of the current block being less than or equal to the maximum transform block size, the ISP related information is not derived, and

wherein, based on the height of the current block being greater than the maximum transform block size and the width of the current block being less than or equal to the maximum transform block size, the ISP related information is not derived.