Chroma intra prediction method and device therefor

1. A video decoding method comprising:

obtaining, with respect to a luma sample and a chroma sample at a same location in a most probable chroma (MPC) mode reference region of a current chroma block, a luma-chroma pair including a luma value of the luma sample and a chroma value of the chroma sample;

reflecting the luma-chroma pair to a luma-chroma 2-dimensional (2D) histogram;

obtaining correlation information of the luma value and the chroma value from the MPC mode reference region of the current chroma block by determining the chroma value corresponding to each luma value, according to the luma-chroma 2D histogram;

determining a prediction value of the chroma sample of the current chroma block from luma samples of a current luma block corresponding to the current chroma block, according to the correlation information; and

decoding the current chroma block based on the prediction value of the chroma sample.

2. The video decoding method of claim 1 , wherein the MPC mode reference region is located at the left, top, and upper left of the current chroma block and is located within a certain sample distance from a boundary of the current chroma block.

3. The video decoding method of claim 2 , wherein the certain sample distance is determined according to MPC mode reference region information obtained from a bitstream.

4. The video decoding method of claim 2 , wherein the certain sample distance is determined according to at least one of a size of the current chroma block, resolution of a current picture, and a slice type.

5. The video decoding method of claim 1 , wherein the MPC mode reference region is a region including all blocks decoded before the decoding of the current chroma block.

6. The video decoding method of claim 1 , wherein the obtaining of the correlation information comprises:

determining luma ranges including a plurality of consecutive luma values; and

determining each corresponding chroma value with respect to the luma ranges, according to the luma-chroma 2D histogram.

7. The video decoding method of claim 1 , wherein the determining of the prediction value of the chroma sample comprises determining prediction values of chroma samples of the current chroma block from a reconstruction result of the current luma block corresponding to the current chroma block after the current luma block is reconstructed.

8. The video decoding method of claim 1 , wherein the determining of the prediction value of the chroma sample comprises determining prediction values of chroma samples of the current chroma block, based on a prediction result of the current luma block corresponding to the current chroma block when the current luma block is predicted according to an inter prediction mode.

9. The video decoding method of claim 1 , wherein the determining of the prediction value of the chroma sample comprises smoothing the prediction value of the chroma sample according to an adjacent sample of the chroma sample.

10. The video decoding method of claim 1 , further comprising obtaining intra mode information of the current chroma block from a bitstream,

wherein the intra mode information indicates one of intra modes available in the current chroma block.

11. The video decoding method of claim 10 , wherein the intra modes comprise at least one of a planar mode, a vertical mode, a horizontal mode, a DC mode, a DM mode, and an MPC mode, and

the obtaining of the correlation information and the determining of the prediction value of the chroma sample are performed when the intra mode information indicates the MPC mode.

12. A video decoding apparatus comprising:

a correlation information obtainer configured to:

obtain, with respect to a luma sample and a chroma sample at a same location in a most probable chroma (MPC) mode reference region of a current chroma block, a luma-chroma pair including a luma value of the luma sample and a chroma value of the chroma sample;

reflect the luma-chroma pair to a luma-chroma 2-dimensional (2D) histogram; and

obtain correlation information of the luma value and the chroma value from the MPC mode reference region of the current chroma block by determining the chroma value corresponding to each luma value, according to the luma-chroma 2D histogram;

a chroma sample predictor configured to determine a prediction value of the chroma sample of the current chroma block from luma samples of a current luma block corresponding to the current chroma block, according to the correlation information; and

a decoder configured to decode the current chroma block based on the prediction value of the chroma sample.

13. A video encoding method comprising:

obtaining, with respect to a luma sample and a chroma sample at a same location in a most probable chroma (MPC) mode reference region of a current chroma block, a luma-chroma pair including a luma value of the luma sample and a chroma value of the chroma sample;

reflecting the luma-chroma pair to a luma-chroma 2-dimensional (2D) histogram;

obtaining correlation information of the luma value and the chroma value from the MPC mode reference region of the current chroma block by determining the chroma value corresponding to each luma value, according to the luma-chroma 2D histogram;

determining a prediction value of the chroma sample of the current chroma block from luma samples of a current luma block corresponding to the current chroma block, according to the correlation information; and

determining an intra mode of the current chroma block among intra modes including an MPC mode, according to a prediction result of the chroma sample.