Colour component prediction method, encoder, decoder, and storage medium

1. A method for predicting a colour component, which is applied to an encoder, the method comprising:

determining multiple groups of corresponding Cross-component Linear Model Prediction (CCLM) parameters using multiple groups of reference samples of a current block when CCLM is used for the current block to determine an intra prediction value of the current block, wherein the CCLM parameter comprises a scale factor and an offset parameter;

determining a target CCLM parameter from the multiple groups of CCLM parameters, setting a CCLM index value according to the target CCLM parameter and signalling the CCLM index value in a bitstream, wherein the CCLM index value is used for indicating to use the target CCLM parameter; and

determining the intra prediction value of the current block according to the target CCLM parameter;

wherein the multiple groups of CCLM parameters correspond to the multiple groups of reference samples respectively.

2. The method according to claim 1 , wherein the determining multiple groups of corresponding CCLM parameters using multiple groups of reference samples of the current block, comprises:

the multiple groups of reference samples comprise pixel sampling points adjacent to the current block;

calculating a group of CCLM parameters corresponding to a group of reference samples using the group of reference samples in the multiple groups of reference samples; and

traversing the multiple groups of reference samples to determine the multiple groups of CCLM parameters.

3. The method according to claim 1 , wherein the determining the target CCLM parameter from the multiple groups of CCLM parameters, comprises:

selecting a group of CCLM parameters corresponding to an optimal value of a target cost function from the multiple groups of CCLM parameters using a Rate Distortion Optimization approach, and determining the group of CCLM parameters as the target CCLM parameter.

4. The method according to claim 1 , wherein the setting the CCLM index value according to the target CCLM parameter and signalling the CCLM index value in the bitstream, comprises:

setting the CCLM index value as an index number corresponding to the target CCLM parameter in the multiple groups of CCLM parameters; and

signalling the CCLM index value in the bitstream.

5. The method according to claim 4 , further comprising:

determining position information of each group of reference samples in the multiple groups of reference samples; and

determining the index number of each group of CCLM parameters in the multiple groups of CCLM parameters according to the position information of each group of reference samples.

6. The method according to claim 5 , wherein the determining the index number of each group of CCLM parameters in the multiple groups of CCLM parameters according to the position information of each group of reference samples, comprises:

determining multiple distance parameters between the multiple groups of reference samples and the current block according to the position information of each group of reference samples; and

setting the index number of each group of CCLM parameters in the multiple groups of CCLM parameters sequentially according to an order of the distance parameters from small to large.

7. The method according to claim 4 , wherein the signalling the CCLM index value in the bitstream, comprises:

signalling the CCLM index value in a data unit containing encoded data of the current block in the bitstream.

8. The method according to claim 1 , wherein the determining the intra prediction value of the current block according to the target CCLM parameter, comprises:

calculating a prediction value of a second colour component of the current block using a linear model according to the target CCLM parameter and a reconstruction value of a first colour component of the current block.

9. The method according to claim 8 , wherein the first colour component is a luma component; and the second colour component is a chroma component.

10. The method according to claim 1 , wherein before determining multiple groups of corresponding CCLM parameters using multiple groups of reference samples of the current block, the method further comprises:

determining a CCLM mode index parameter, wherein the CCLM mode index parameter is used for indicating a CCLM mode used for the current block, and the CCLM mode is used for indicating a calculation and derivation approach of determining the intra prediction value using CCLM; and

signalling the CCLM mode index parameter in a bitstream.

11. The method according to claim 1 , further comprising:

setting a prediction mode parameter of the current block and signalling the prediction mode parameter in the bitstream when CCLM is used for the current block to determine the intra prediction value of the current block.

12. A method for predicting a colour component, which is applied to a decoder, the method comprising:

parsing a bitstream and determining a prediction mode parameter of a current block;

parsing the bitstream and determining a Cross-component Linear Model Prediction (CCLM) index value of the current block when the prediction mode parameter indicates to determine an intra prediction value of the current block using CCLM;

determining a target CCLM parameter of the current block according to the CCLM index value, wherein the target CCLM parameter comprises a scale factor and an offset parameter; and

determining the intra prediction value of the current block according to the target CCLM parameter;

wherein the multiple groups of CCLM parameters correspond to the multiple groups of reference samples respectively.

13. The method according to claim 12 , wherein the determining the target CCLM parameter of the current block according to the CCLM index value, comprises:

determining a target reference sample of the current block according to the CCLM index value, wherein the target reference sample is one or more pixel sampling points adjacent to the current block; and

determining the target CCLM parameter of the current block according to the target reference sample.

14. The method according to claim 13 , wherein the determining the target reference sample of the current block according to the CCLM index value, comprises:

determining the target reference sample from multiple groups of reference samples of the current block according to an index number indicated by the CCLM index value, wherein each group of reference samples in the multiple groups of reference samples comprises pixel sampling point(s) at one or more preset positions adjacent to the current block.

15. The method according to claim 12 , wherein the determining the target CCLM parameter of the current block according to the CCLM index value, comprises:

determining multiple groups of corresponding CCLM parameters using multiple groups of reference samples of the current block, wherein each group of reference samples in the multiple groups of reference samples comprises pixel sampling point(s) at one or more preset positions adjacent to the current block; and

using a group of CCLM parameters indicated by the CCLM index value in the multiple groups of CCLM parameters as the target CCLM parameter.

16. The method according to claim 12 , wherein the determining the intra prediction value of the current block according to the target CCLM parameter, comprises:

calculating a prediction value of a second colour component of the current block using a linear model according to the target CCLM parameter and a reconstruction value of a first colour component of the current block.

17. The method according to claim 16 , wherein the first colour component is a luma component; and the second colour component is a chroma component.

18. The method according to claim 12 , wherein after parsing the bitstream and determining the prediction mode parameter of the current block, the method further comprises:

parsing the bitstream and determining a CCLM mode index parameter of the current block when the prediction mode parameter indicates to determine the intra prediction value of the current block using CCLM, wherein the CCLM mode index parameter is used for indicating a CCLM mode used for the current block, and the CCLM mode is used for indicating a calculation and derivation approach of determining the intra prediction value using CCLM.

19. An encoder comprising a first processor and a first memory storing instructions executable for the first processor, wherein when the instructions are executed, the first processor implements the method according to claim 1 .

20. A decoder comprising a second processor and a second memory storing instructions executable for the second processor, wherein when the instructions are executed, the second processor implements the method according to claim 12 .