Method and apparatus for cross-component filtering

A method for video decoding in a decoder, comprising:

• decoding coded information of a chroma coding block (CB) from a coded video bitstream, the coded information indicating that a cross-component filter is applied to the chroma CB based on a corresponding luma CB;
• generating a down-sampled luma CB by applying a down-sampling filter to the corresponding luma CB, a chroma horizontal subsampling factor, and a chroma vertical subsampling factor between the chroma CB and the down-sampled luma CB being one;
• generating a first intermediate CB by applying a loop filter to the chroma CB;
• generating a second intermediate CB by applying, to the down-sampled luma CB, the cross-component filter applied to the chroma CB, a filter shape of the cross-component filter being independent of a chroma subsampling format and a chroma sample type of the chroma CB, the chroma sample type indicating a relative position of a chroma sample with respect to at least one luma sample in the corresponding luma CB;
• and
• determining a filtered chroma CB based on the first intermediate CB and the second intermediate CB by combining the loop filtered chroma CB with the cross-component filtered down-sampled luma CB, wherein
• a number of filter coefficients of the cross-component filter is signaled in the coded video bitstream;
• and
• the filter shape of the cross-component filter is determined based on the number of filter coefficients.

An apparatus for video decoding, comprising:

• processing circuitry configured to:
• decode coded information of a chroma coding block (CB) from a coded video bitstream, the coded information indicating that a cross-component filter is applied to the chroma CB, the coded information further indicating a chroma subsampling format and a chroma sample type that indicates a relative position of a chroma sample with respect to at least one luma sample in a corresponding luma CB;
• determine a filter shape of the cross-component filter applied to the chroma CB based on at least one of the chroma subsampling format or the chroma sample type;
• generate a first intermediate CB by applying a loop filter to the chroma CB;
• generate a second intermediate CB by applying, to the corresponding luma CB, the cross-component filter applied to the chroma CB and having the determined filter shape;
• and
• determine a filtered chroma CB based on the first intermediate CB and the second intermediate CB by combining the loop filtered chroma CB with the cross-component filtered luma CB, wherein
• a number of filter coefficients of the cross-component filter is signaled in the coded video bitstream;
• and
• the filter shape of the cross-component filter is determined based on the number of filter coefficients and the at least one of the chroma subsampling format or the chroma sample type.