Generation of chroma components using cross-component adaptive loop filters

A method for video decoding, comprising:

• decoding coded information of a chroma coding block (CB) from a coded video bitstream, the coded information including (i) an indication that a cross-component filter is applied to the chroma CB based on a corresponding luma CB, and (ii) a number of filter coefficients of the cross-component filter;
• 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, a 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 adding the loop filtered chroma CB to the cross-component filtered down-sampled luma CB, wherein
• the filter coefficients of the cross-component filter are decoded from the coded video bitstream using fixed-length coding, where a range of the filter coefficients of the cross-component filter is less than or equal to K bits, K being a positive integer, and
• the filter shape of the cross-component filter is determined based on the number of filter coefficients.

An apparatus for video encoding, comprising:

• processing circuitry configured to:
• decode coded information of a chroma coding block (CB) from a coded video bitstream, the coded information including (i) an indication that a cross-component filter is applied to the chroma CB, (ii) an indication of 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, and (iii) a number of filter coefficients of the cross-component filter;
• determine a filter shape of the cross-component filter applied to a chroma CB;
• generate a first intermediate CB by applying a loop filter to the chroma CB;
• generate a second intermediate CB by applying, to a 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 adding the loop filtered chroma CB to the cross-component filtered luma CB, wherein
• the filter coefficients of the cross-component filter are decoded from the coded video bitstream using fixed-length coding, where a range of the filter coefficients of the cross-component filter is less than or equal to K bits, K being a positive integer, and
• the filter shape of the cross-component filter is determined based on the number of filter coefficients and based on at least one of (i) the chroma subsampling format or (ii) the chroma sample type.