Weight derivation of multiple reference line for intra prediction fusion

A method of video decoding in a decoder, comprising:

• decoding prediction information of a current block in a current picture from a coded bitstream, the prediction information indicating an intra prediction mode being applied to the current block with a multiple reference line (MRL) prediction;
• receiving an MRL index i from the coded bitstream indicating that an ith entry in a MRL list corresponds to a first reference line;
• determining that an (i+1)th entry in the MRL list corresponds to a second reference line;
• and
• reconstructing a sample in the current block using intra prediction fusion that is based on multiple reference lines of the current block, the first reference line corresponding to the ith entry in the MRL list and the second reference line corresponding to the (i+1)th entry in the MRL list, the first reference line and the second reference line not being spatially adjacent.

A method of video encoding, comprising:

• encoding prediction information indicating that an intra prediction mode with multiple reference line (MRL) prediction is applied to a current block in a current picture, the current block being predicted based on a first reference line and a second reference line that is different from the first reference line, a first weight candidate being applied to the first reference line, a second weight candidate being applied to the second reference line, each weight candidate combination in a plurality of weight candidate combinations including a respective first weight candidate and a respective second weight candidate, wherein
• for each weight candidate combination in the plurality of weight candidate combinations,
• a subset of samples in the current block is predicted using intra prediction fusion that is based on the first reference line weighted by the respective first weight candidate and the second reference line weighted by the respective second weight candidate, the subset of samples including (i) top samples in a top-most row in the current block and (ii) left samples in a left-most column in the current block;
• and
• a gradient cost is determined based on the predicted subset of samples in the current block and reconstructed samples outside the current block, the reconstructed samples outside the current block including samples that neighbor the predicted subset of samples in the current block;
• and
• a weight candidate combination is selected based on the determined gradient cost corresponding to each weight candidate combination.