Image encoding/decoding method and device using maximum transform size restriction of chroma component encoding block, 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;

generating a prediction block of the current block based on intra block copy (IBC) prediction mode information, based on the prediction mode of the current block being an IBC prediction mode;

determining a size of a transform block of the current block based on a color component of the current block;

generating a residual block of the current block based on the size of the transform block; and

reconstructing the current block based on the prediction block and the residual block of the current block,

wherein the current block is a chroma block, and

wherein, based on the transform block being split into a plurality of lower-layer transform blocks, a top-left position of the lower-layer transform blocks is determined based on a maximum width and a maximum height of the transform block.

2. The image decoding method of claim 1 ,

wherein a width of the transform block is determined based on the maximum width of the transform block, and

wherein the maximum width of the transform block is determined based on a maximum size of a luma transform block corresponding to the current block and a color format of the current block.

3. The image decoding method of claim 1 ,

wherein a height of the transform block is determined based on the maximum height of the transform block, and

wherein the maximum height of the transform block is determined based on a maximum size of a luma transform block corresponding to the current block and a color format of the current block.

4. The image decoding method of claim 1 ,

wherein, based on a color format of the current block being a format specifying that a width and height of a chroma block is half a width of a luma block corresponding thereto, the maximum width of the transform block is determined to be half a maximum width of a luma transform block corresponding to the current block, and the maximum height of the transform block is determined to be half a maximum height of the luma transform block.

5. The image decoding method of claim 1 ,

wherein the maximum width of the transform block is determined based on a maximum size of a luma transform block corresponding to the current block and a color format of the current block, and

wherein the maximum height of the transform block is determined based on the maximum size of the luma transform block and the color format of the current block.

6. The image decoding method of claim 1 ,

wherein the lower-layer transform blocks are generated by vertically splitting the current block, based on a width of the transform block being greater than the maximum width of the transform block, and

wherein the maximum width of the transform block is determined based on a maximum size of a luma transform block corresponding to the current block and a color format of the current block.

7. The image decoding method of claim 6 ,

wherein the plurality of lower-layer transform blocks include a first lower-layer block and a second lower-layer transform block, and

wherein a width of the first lower-layer transform block and a width of the second lower-layer transform block are determined to be the maximum width of the transform block.

8. The image decoding method of claim 1 ,

wherein the lower-layer transform blocks are generated by horizontally splitting the current block, based on a height of the transform block being greater than the maximum height of the transform block, and

wherein the maximum height of the transform block is determined based on a maximum height of a luma transform block corresponding to the current block and a color format of the current block.

9. The image decoding method of claim 8 ,

wherein the plurality of lower-layer transform blocks include a third lower-layer block and a fourth lower-layer transform block, and

wherein a height of the third lower-layer transform block and a height of the fourth lower-layer transform block are determined to be the maximum height of the transform block.

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

determining a current block by splitting an image;

generating a prediction block of the current block by performing intra block copy (IBC) prediction on the current block;

generating a residual block of the current block based on the prediction block; and

encoding prediction mode information of the current block,

wherein the residual block is encoded based on a size of a transform block of the current block,

wherein the current block is a chroma block, and

wherein, based on the transform block being split into a plurality of lower-layer transform blocks, a top-left position of the lower-layer transform blocks is determined based on a maximum width and a maximum height of the transform block.

11. A non-transitory computer-readable recording medium storing a bitstream generated by the image encoding method of claim 10 .

12. A method of transmitting a bitstream generated by an image encoding method, the image encoding method comprising:

determining a current block by splitting an image;

generating a prediction block of the current block by performing intra block copy (IBC) prediction on the current block;

generating a residual block of the current block based on the prediction block; and

encoding prediction mode information of the current block,

wherein the residual block is encoded based on a size of a transform block of the current block,

wherein the current block is a chroma block, and

wherein, based on the transform block being split into a plurality of lower-layer transform blocks, a top-left position of the lower-layer transform blocks is determined based on a maximum width and a maximum height of the transform block.