In-loop filtering method and device

1. An in-loop filtering method comprising:

determining a target filter for a chrominance component of a current block of an image from a plurality of cross-component adaptive loop filtering (ALF) filters;

determining target filter coefficients for the chrominance component of the current block according to the chrominance component after ALF and a luminance component of the current block without ALF;

filtering the chrominance component after ALF according to the target filter and the target filter coefficients;

determining a filtered chrominance component of the current block according to the chrominance component after being filtered with the target filter coefficients and the chrominance component after the ALF;

encoding according to the filtered chrominance component of the current block; and

encoding a total number of the plurality of cross-component ALF filters as a syntax element of a bitstream;

wherein the syntax element for indicating the total number of the plurality of cross-component ALF filters is only located in an adaptation parameter set syntax of the image, and not present in an image header and/or a slice header.

2. The in-loop filtering method according to claim 1 , wherein:

the chrominance component after ALF is the chrominance component after sample adaptive offset (SAO) filtering and ALF sequentially.

3. The in-loop filtering method according to claim 1 , wherein:

the luminance component without ALF is the luminance component after sample adaptive offset (SAO) and without ALF.

4. The in-loop filtering method according to claim 1 , wherein encoding the total number of the plurality of cross-component ALF filters as the syntax element includes:

encoding the total number of the plurality of cross-component ALF filters using a truncated binary code.

5. The in-loop filtering method according to claim 1 ,

wherein the syntax element is a first syntax element;

the method further comprising:

encoding an index of the target filter as a second syntax element.

6. The in-loop filtering method according to claim 5 , wherein encoding the index of the target filter as the second syntax element includes:

encoding the index of the target filter using a truncated binary code.

7. An in-loop filtering method comprising:

decoding a total number of cross-component adaptive loop filtering (ALF) filters and an index of a target filter from a stream, the target filter being an ALF filter adopted by a chrominance component of a current block of an image and a target cross-component ALF filter;

decoding target filter coefficients for the chrominance component from the stream, the target filter coefficients being coefficients in the target cross-component ALF filter;

performing filtering on the chrominance component after ALF according to the target cross-component ALF filter and the target filter coefficients; and

determining a filtered chrominance component of the current block according to the chrominance component filtered with the target filter coefficients and the chrominance component after ALF;

wherein a syntax element for indicating the total number of the plurality of cross-component ALF filters is only located in an adaptation parameter set syntax of the image, and not present in an image header and/or a slice header.

8. The in-loop filtering method according to claim 7 , wherein:

the chrominance component after ALF is the chrominance component after sample adaptive offset (SAO) filtering and ALF sequentially.

9. The in-loop filtering method according to claim 7 , wherein:

a luminance component of the current block without ALF is the luminance component of the current block after sample adaptive offset (SAO) filtering and without ALF.

10. The in-loop filtering method according to claim 7 , wherein decoding the total number of the cross-component ALF filters and the index of the target filter from the stream includes:

decoding the total number of the cross-component ALF filters and/or the index of the target filter using a truncated binary code.

11. A bitstream generation method comprising:

determining a target filter for a chrominance component of a current block of an image from a plurality of cross-component adaptive loop filtering (ALF) filters;

determining target filter coefficients for the chrominance component of the current block according to the chrominance component after ALF and a luminance component of the current block without ALF;

filtering the chrominance component after ALF according to the target filter and the target filter coefficients;

determining a filtered chrominance component of the current block according to the chrominance component after being filtered with the target filter coefficients and the chrominance component after the ALF;

encoding according to the filtered chrominance component of the current block to generate a bitstream; and

encoding a total number of the plurality of cross-component ALF filters as a syntax element of the bitstream;

wherein a syntax element for indicating the total number of the plurality of cross-component ALF filters is only located in an adaptation parameter set syntax of the image, and not present in an image header and/or a slice header.

12. The bitstream generation method according to claim 11 , wherein:

the chrominance component after ALF is the chrominance component after sample adaptive offset (SAO) filtering and ALF sequentially.

13. The bitstream generation method according to claim 11 , wherein:

the luminance component without ALF is the luminance component after sample adaptive offset (SAO) and without ALF.

14. The bitstream generation method according to claim 11 , wherein encoding the total number of the plurality of cross-component ALF filters as the syntax element includes:

encoding the total number of the plurality of cross-component ALF filters using a truncated binary code.