Chroma intra prediction method and device

1. A chroma intra prediction method, applied to a decoder, the method comprising:

parsing bitstream data corresponding to a current chroma block, and determining that a prediction mode corresponding to the current chroma block is a direct mode (DM);

before determining a set of chroma prediction modes based on at least one modified candidate mode, acquiring a linear mode corresponding to the current chroma block from the bitstream data;

determining an intra prediction mode of the current chroma block from a set of chroma prediction modes, wherein the set of chroma prediction modes comprises at least one of the DM or the linear mode; and

determining a reconstructed value of the current chroma block according to the intra prediction mode.

2. The method of claim 1 , wherein when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes comprises a diagonal angular mode with prediction direction index number 66.

3. The method of claim 1 , further comprising determining the at least one modified candidate mode, wherein:

when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes is determined based on the at least one modified candidate mode; and

determining the at least one modified candidate mode comprises adjusting a mode with a prediction direction index number 66 by a first angle in a first angular direction and adjusting a mode with a prediction direction index number 2 by the first angle in a direction opposite to the first angular direction to obtain derived angles of the at least one modified candidate mode;

the prediction direction index number 66 points in a top-right direction; and

the prediction direction index number 2 points in a bottom-left direction.

4. The method of claim 2 , wherein

when a luma prediction mode corresponding to the DM is the DC mode, the set of chroma prediction modes is determined at least according to the Planar mode and the at least one modified candidate mode, and

when a luma prediction mode corresponding to the DM is the Planar mode, the set of chroma prediction modes is determined at least according to the DC mode and the at least one modified candidate mode.

5. The method of claim 1 , wherein when a luma prediction mode corresponding to the DM is one of a DC mode, Planar mode, VER mode or HOR mode, the set of chroma prediction modes comprises an angular mode with an index number 66.

6. A chroma intra prediction method, applied to an encoder, the method comprising:

determining that a prediction mode corresponding to a current chroma block is a direct mode (DM);

before determining a set of chroma prediction modes based on at least one modified candidate mode, acquiring a linear mode corresponding to the current chroma block from bitstream data;

determining an intra prediction mode of the current chroma block from a set of chroma prediction modes, wherein the set of chroma prediction modes comprises at least one of the DM or the linear mode; and

determining a reconstructed value of the current chroma block according to the intra prediction mode.

7. The method of claim 6 , wherein when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes comprises a diagonal angular mode with prediction direction index number 66 pointing towards the top-right direction.

8. The method of claim 6 , further comprising determining the at least one modified candidate mode wherein:

when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes is determined based on the at least one modified candidate mode; and

determining the at least one modified candidate mode comprises adjusting a mode with a prediction direction index number 66 by a first angle in a first angular direction and adjusting a mode with a prediction direction index number 2 by the first angle in a direction opposite to the first angular direction to obtain derived angles of the at least one modified candidate mode;

the prediction direction index number 66 points in a top-right direction; and

the prediction direction index number 2 points in a bottom-left direction.

9. The method of claim 7 , wherein

when a luma prediction mode corresponding to the DM is the DC mode, the set of chroma prediction modes is determined at least according to the Planar mode and the at least one modified candidate mode,

when a luma prediction mode corresponding to the DM is the Planar mode, the set of chroma prediction modes is determined at least according to the DC mode and the at least one modified candidate mode.

10. The method of claim 6 , wherein when a luma prediction mode corresponding to the DM is one of a DC mode, Planar mode, VER mode or HOR mode, the set of chroma prediction modes comprises an angular mode with an index number 66.

11. A chroma intra prediction device, applied to a decoder, the device comprising:

a processor, a memory storing instructions executable by the processor, a communication interface, and a bus for connecting the processor, the memory and the communication interface, wherein the processor is configured to execute the instructions to perform operations of:

parsing bitstream data corresponding to a current chroma block, and determining that a prediction mode corresponding to the current chroma block is a direct mode (DM);

before determining a set of chroma prediction modes based on at least one modified candidate mode, acquiring a linear mode corresponding to the current chroma block from the bitstream data;

determining an intra prediction mode of the current chroma block from a set of chroma prediction modes, wherein the set of chroma prediction modes comprises at least one of the DM or the linear mode; and

determining a reconstructed value of the current chroma block according to the intra prediction mode.

12. The device of claim 11 , wherein when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes comprises a diagonal angular mode with prediction direction index number 66.

13. The device of claim 11 , further comprising determining the at least one modified candidate mode, wherein:

when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes is determined based on the at least one modified candidate mode; and

determining the at least one modified candidate mode comprises adjusting a mode with a prediction direction index number 66 by a first angle in a first angular direction and adjusting a mode with a prediction direction index number 2 by the first angle in a direction opposite to the first angular direction to obtain derived angles of the at least one modified candidate mode;

the prediction direction index number 66 points in a top-right direction; and

the prediction direction index number 2 points in a bottom-left direction.

14. The device of claim 12 , wherein:

when a luma prediction mode corresponding to the DM is the DC mode, the set of chroma prediction modes is determined at least according to the Planar mode and the at least one modified candidate mode; and

when a luma prediction mode corresponding to the DM is the Planar mode, the set of chroma prediction modes is determined at least according to the DC mode and the at least one modified candidate mode.

15. The device of claim 11 , when a luma prediction mode corresponding to the DM is one of a DC mode, Planar mode, VER mode or HOR mode, the set of chroma prediction modes comprises an angular mode with an index number 66.

16. A chroma intra prediction device, applied to an encoder, the device comprising:

a processor, a memory storing instructions executable by the processor, a communication interface, and a bus for connecting the processor, the memory and the communication interface, wherein the processor is configured to execute the instructions to perform operations of:

determining that a prediction mode corresponding to a current chroma block is a direct mode (DM);

before determining a set of chroma prediction modes based on at least one modified candidate mode, acquiring a linear mode corresponding to the current chroma block from bitstream data;

determining an intra prediction mode of the current chroma block from a set of chroma prediction modes, wherein the set of chroma prediction modes comprises at least one of the DM or the linear mode; and

determining a reconstructed value of the current chroma block according to the intra prediction mode.

17. The device of claim 16 , wherein when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes comprises a diagonal angular mode with prediction direction index number 66.

18. The device of claim 16 , further comprising determining the at least one modified candidate mode, wherein:

when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes is determined based on the at least one modified candidate mode; and

determining the modified candidate modes comprises adjusting a mode with a prediction direction index number 66 by a first angle in a first angular direction and adjusting a mode with a prediction direction index number 2 by the first angle in a direction opposite to the first angular direction to obtain derived angles of the modified candidate modes;

the prediction direction index number 66 points in a top-right direction; and

the prediction direction index number 2 points in a bottom-left direction.

19. The device of claim 17 , wherein

when a luma prediction mode corresponding to the DM is the DC mode, the set of chroma prediction modes is determined at least according to the Planar mode and the at least one modified candidate mode,

when a luma prediction mode corresponding to the DM is the Planar mode, the set of chroma prediction modes is determined at least according to the DC mode and the at least one modified candidate mode.

20. The device of claim 16 , wherein when a luma prediction mode corresponding to the DM is one of a DC mode, Planar mode, VER mode or HOR mode, the set of chroma prediction modes comprises an angular mode with an index number 66.

21. The method of claim 1 , wherein when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the intra prediction mode comprises at least one of a diagonal angular mode with prediction direction index number 34 pointing in the top-left direction or a diagonal angular mode with prediction direction index number 2 pointing in the bottom-left direction.

22. The method of claim 1 , wherein the linear mode is LM, LM_T or LM_L.