Cross-component adaptive loop filtering-based image coding apparatus and method
According to one embodiment of the present document, an in-loop filtering procedure in an image/video coding procedure may include a cross-component adaptive loop filtering procedure. CCALF according to the present embodiment can increase the accuracy of in-loop filtering.
1. A method for image decoding performed by a decoding apparatus, the method comprising:
receiving image information through a bitstream;
generating reconstructed luma samples and reconstructed chroma samples based on the image information;
performing an adaptive loop filtering (ALF) process on the reconstructed chroma samples to generate filtered reconstructed chroma samples; and
performing a cross-component filtering process on the filtered reconstructed chroma samples to generate modified filtered reconstructed chroma samples,
wherein the image information includes information on cross-component filtering, and
the performing of the cross-component filtering process includes:
deriving a number of cross-component filters for the cross-component filtering based on the information on the cross-component filtering;
deriving cross-component filter coefficients for the cross-component filtering process based on the number of cross-component filters; and
generating the modified filtered reconstructed chroma samples based on the filtered reconstructed chroma samples and the cross-component filter coefficients,
wherein the image information includes a sequence parameter set (SPS) and slice header information,
wherein the SPS includes an ALF enabled flag related to whether the ALF process is enabled,
wherein based on a determination that a value of the ALF enabled flag is 1, the SPS includes a cross-component adaptive loop filter (CCALF) enabled flag related to whether the cross-component filtering is enabled,
wherein based on a determination that a value of the ALF enabled flag included in the SPS is 1, the slice header information includes an ALF enabled flag related to whether the ALF is enabled,
wherein based on a determination that a value of the ALF enabled flag included in the slice header information is 1 and a value of the CCALF enabled flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chroma samples, and
wherein based on a value of the information on whether the CCALF is enabled for the filtered reconstructed chroma samples being 1, the slice header information includes identification (ID) information of adaptation parameter sets (APSs) including ALF data used to derive the cross-component filter coefficients,
wherein the image information includes information on a coding tree unit, and
wherein the information on the coding tree unit includes:
information on whether a cross-component filter is applied to a Cb color component of the current block, and information on whether a cross-component filter is applied to a Cr color component of the current block, and
information on a filter set index of a cross-component filter applied to the Cb color component of the current block, and information on a filter set index of a cross-component filter applied to the Cr color component of the current block.
2. The method of claim 1 ,
wherein the ALF data includes information on a number of cross-component filters for the Cb color component and information on a number of cross-component filters for the Cr color component.
3. The method of claim 2 , wherein
the ALF data includes information on absolute values of cross-component filter coefficients for the Cb color component and information on signs of cross-component filter coefficients for the Cb color component, based on the information on the number of cross-component filters for the Cb color component, and
the cross-component filter coefficients for the Cb color component are derived based on the information on the absolute values of the cross-component filter coefficients for the Cb color component and the information on the signs of the cross-component filter coefficients for the Cb color component.
4. The method of claim 2 , wherein
the ALF data includes information on absolute values of cross-component filter coefficients for the Cr color component and information on signs of cross-component filter coefficients for the Cr color component, based on the information on the number of cross-component filters for the Cr color component, and
the cross-component filter coefficients for the Cr color component are derived based on the information on the absolute values of the cross-component filter coefficients for the Cr color component and the information on the signs of the cross-component filter coefficients for the Cr color component.
5. A method for image encoding performed by an encoding apparatus, the method comprising:
generating reconstructed luma samples and reconstructed chroma samples of a current block in a current picture;
deriving adaptive loop filtering (ALF) filter coefficients for an ALF process;
generating ALF-related information based on the ALF filter coefficients;
deriving cross-component filters and cross-component filter coefficients for a cross-component filtering process;
generating cross-component filtering-related information based on the cross-component filters and the cross-component filter coefficients; and
encoding image information including information for generating the reconstructed samples, the ALF-related information, and the cross-component filtering-related information,
wherein the cross-component filtering-related information includes information on a number of the cross-component filters and information on the cross-component filter coefficients,
wherein the image information includes a sequence parameter set (SPS) and slice header information,
wherein the SPS includes an ALF enabled flag related to whether the ALF process is enabled,
wherein based on a determination that a value of the ALF enabled flag is 1, the SPS includes a cross-component adaptive loop filter (CCALF) enabled flag related to whether the cross-component filtering is enabled,
wherein based on a determination that a value of the ALF enabled flag included in the SPS is 1, the slice header information includes an ALF enabled flag related to whether the ALF is enabled,
wherein based on a determination that a value of the ALF enabled flag included in the slice header information is 1 and a value of the CCALF enabled flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chroma samples, and
wherein based on a value of the information on whether the CCALF is enabled for the filtered reconstructed chroma samples being 1, the slice header information includes identification (ID) information of adaptation parameter sets (APSs) including ALF data used to derive the cross-component filter coefficients,
wherein the image information includes information on a coding tree unit, and
wherein the information on the coding tree unit includes:
information on whether a cross-component filter is applied to a Cb color component of the current block, and information on whether a cross-component filter is applied to a Cr color component of the current block, and
information on a filter set index of a cross-component filter applied to the Cb color component of the current block, and information on a filter set index of a cross-component filter applied to the Cr color component of the current block.
6. The method of claim 5 ,
wherein the ALF data includes information on a number of cross-component filters for the Cb color component and the second ALF data includes information on a number of cross-component filters for the Cr color component.
7. The method of claim 6 , wherein
the ALF data includes information on absolute values of cross-component filter coefficients for the Cb color component and information on signs of cross-component filter coefficients for the Cb color component, based on the information on the number of cross-component filters for the Cb color component, and
the cross-component filter coefficients for the Cb color component are derived based on the information on the absolute values of the cross-component filter coefficients for the Cb color component and the information on the signs of the cross-component filter coefficients for the Cb color component.
8. The method of claim 6 , wherein
the ALF data includes information on absolute values of cross-component filter coefficients for the Cr color component and information on signs of cross-component filter coefficients for the Cr color component, based on the information on the number of cross-component filters for the Cr color component, and
the cross-component filter coefficients for the Cr color component are derived based on the information on the absolute values of the cross-component filter coefficients for the Cr color component and the information on the signs of the cross-component filter coefficients for the Cr color component.
9. A non-transitory computer-readable storage medium storing a bitstream generated by an image encoding method, the image encoding method comprising:
generating reconstructed luma samples and reconstructed chroma samples of a current block in a current picture;
deriving adaptive loop filtering (ALF) filter coefficients for an ALF process;
generating ALF-related information based on the ALF filter coefficients;
deriving cross-component filters and cross-component filter coefficients for a cross-component filtering process;
generating cross-component filtering-related information based on the cross-component filters and the cross-component filter coefficients; and
encoding image information to generate the bitstream, wherein the image information includes information for generating the reconstructed samples, the ALF-related information, and the cross-component filtering-related information,
wherein the cross-component filtering-related information includes information on a number of the cross-component filters and information on the cross-component filter coefficients,
wherein the image information includes a sequence parameter set (SPS) and slice header information,
wherein the SPS includes an ALF enabled flag related to whether the ALF process is enabled,
wherein based on a determination that a value of the ALF enabled flag is 1, the SPS includes a cross-component adaptive loop filter (CCALF) enabled flag related to whether the cross-component filtering is enabled,
wherein based on a determination that a value of the ALF enabled flag included in the SPS is 1, the slice header information includes an ALF enabled flag related to whether the ALF is enabled,
wherein based on a determination that a value of the ALF enabled flag included in the slice header information is 1 and a value of the CCALF enabled flag included in the SPS is 1, the slice header information includes information on whether the CCALF is enabled for the filtered reconstructed chroma samples, and
wherein based on a value of the information on whether the CCALF is enabled for the filtered reconstructed chroma samples being 1, the slice header information includes identification (ID) information of adaptation parameter sets (APSs) including ALF data used to derive the cross-component filter coefficients,
wherein the image information includes information on a coding tree unit, and
wherein the information on the coding tree unit includes:
information on whether a cross-component filter is applied to a Cb color component of the current block, and information on whether a cross-component filter is applied to a Cr color component of the current block, and
information on a filter set index of a cross-component filter applied to the Cb color component of the current block, and information on a filter set index of a cross-component filter applied to the Cr color component of the current block.