Image encoding/decoding method and device for determining division mode on basis of prediction mode type determined according to color format, and method for transmitting bitstream

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

obtaining a current block by splitting an image;

determining prediction mode characteristic information based on encoding information of the current block;

determining a prediction mode type of a lower-layer block split from the current block based on the prediction mode characteristic information;

obtaining the lower-layer block by splitting the current block; and

decoding the lower-layer block based on the determined prediction mode type of the lower-layer block,

wherein the prediction mode characteristic information is determined based on a color format of the current block.

2. The image decoding method of claim 1 ,

wherein the obtaining the lower-layer block by splitting the current block is performed by determining a splitting structure of the lower-layer block based on the prediction mode type of the lower-layer block; and

wherein the splitting structure of the lower-layer block is determined to be a dual tree splitting structure, based on the prediction mode type of the lower-layer block being an intra prediction mode type.

3. The image decoding method of claim 2 ,

wherein splitting availability of a luma block and a chroma block for the current block is independently determined, based on the splitting structure of the lower-layer block being determined to be the dual tree splitting structure, and

wherein the splitting availability of the chroma block is determined based on the color format.

4. The image decoding method of claim 1 , wherein the prediction mode characteristic information is determined to be a first value, based on the color format of the current block being a monochrome format or a 4:4:4 format.

5. The image decoding method of claim 4 , wherein the prediction mode type of the lower-layer block is determined to be a prediction mode type of the current block, based on the prediction mode characteristic information being a first value.

6. The image decoding method of claim 1 , wherein the prediction mode characteristic information is determined to be a first value, based on the number of luma samples of the current block being 64, the splitting mode of the current block being a binary splitting mode and the color format of the current block being a predetermined format.

7. The image decoding method of claim 1 , wherein the prediction mode characteristic information is determined to be a first value, based on the number of luma samples of the current block being 128, the splitting mode of the current block being a ternary splitting mode and the color format of the current block being a predetermined format.

8. The image decoding method of claim 7 , wherein the predetermined format is a monochrome format or a 4:4:4 format.

9. The image decoding method of claim 1 , wherein the prediction mode characteristic information is determined depending on whether a slice to which the current block belongs is an I slice, based on the color format of the current block being a 4:2:0 format, the number of luma samples of the current block being 64 and the splitting mode of the current block being a binary splitting mode.

10. The image decoding method of claim 1 , wherein the prediction mode characteristic information is determined depending on whether a slice to which the current block belongs is an I slice, based on the color format of the current block being a 4:2:0 format, the number of luma samples of the current block being 128 and the splitting mode of the current block being a ternary splitting mode.

11. The image decoding method of claim 10 ,

wherein the prediction mode characteristic information is determined to be a second value, based on the slice to which the current block belongs being an I slice, and

wherein the prediction mode type of the lower-layer block is determined to be an intra prediction mode type, based on the prediction mode characteristic information being the second value.

12. The image decoding method of claim 8 ,

wherein the prediction mode characteristic information is determined to be a third value, based on the slice to which the current block belongs being not an I slice,

wherein the prediction mode type of the lower-layer block is determined based on mode constraint information obtained from a bitstream, based on the prediction mode characteristic information being the third value,

wherein the mode constraint information specifies whether an inter prediction mode is allowed, and

wherein the prediction mode type of the lower-layer block is determined to be an inter prediction mode type, based on the mode constraint information specifying that the inter prediction mode is allowed.

13. An image decoding apparatus comprising:

a memory; and

at least one processor,

wherein the at least one processor is configured to:

obtain a current block by splitting an image;

determine prediction mode characteristic information based on encoding information of the current block;

determine a prediction mode type of a lower-layer block split from the current block based on the prediction mode characteristic information;

obtain the lower-layer block by splitting the current block; and

decode the lower-layer block based on the determined prediction mode type of the lower-layer block,

wherein the prediction mode characteristic information is determined based on a color format of the current block.

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

obtaining a current block by splitting an image;

determining prediction mode characteristic information based on encoding information of the current block;

determining a prediction mode type of a lower-layer block split from the current block based on the prediction mode characteristic information;

obtaining the lower-layer block by splitting the current block; and

encoding the lower-layer block based on the determined prediction mode type of the lower-layer block,

wherein the prediction mode characteristic information is determined based on a color format of the current block.

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