A method of decoding a bitstream by an electronic device, the method comprising: determining a block unit having an intra prediction mode from an image frame according to the bitstream; determining, based on a specific reference line candidate determined based on a reference line index and a most probable mode, mpm, flag of the block unit, the intra prediction mode of the block unit, wherein: a plurality of most probable modes is selected from a plurality of intra mode candidates, a plurality of remaining mode candidates is generated by removing the plurality of most probable modes from a plurality of intra mode candidates, the intra prediction mode is determined, without parsing the mpm flag, from the plurality of most probable modes when the specific reference line candidate is different from a first one of a plurality of reference line candidates; the intra prediction mode is determined from the plurality of most probable modes when the specific reference line candidate is identical to the first one of the plurality of reference line candidates and the mpm flag is equal to a predefined value, the intra prediction mode is determined from the plurality of remaining mode candidates when the specific reference line candidate is identical to the first one of the plurality of reference line candidates and the mpm flag is different from the predefined value, and the first one of the plurality of reference line candidates is immediately adjacent to the block unit; determining the intra prediction mode of the block unit based on a first one of a plurality of mode indices, when the intra prediction mode is selected from the plurality of most probable modes, wherein the first one of the plurality of mode indices is an mpm index; determining the intra prediction mode of the block unit based on a second one of the plurality of mode indices, when the intra prediction mode is selected from the plurality of remaining mode candidates; and reconstructing the block unit of the image frame based on the intra prediction mode. determining a block unit having an intra prediction mode from an image frame according to the bitstream; determining, based on a specific reference line candidate determined based on a reference line index and a most probable mode, mpm, flag of the block unit, the intra prediction mode of the block unit, wherein: a plurality of most probable modes is selected from a plurality of intra mode candidates, a plurality of remaining mode candidates is generated by removing the plurality of most probable modes from a plurality of intra mode candidates, the intra prediction mode is determined, without parsing the mpm flag, from the plurality of most probable modes when the specific reference line candidate is different from a first one of a plurality of reference line candidates; the intra prediction mode is determined from the plurality of most probable modes when the specific reference line candidate is identical to the first one of the plurality of reference line candidates and the mpm flag is equal to a predefined value, the intra prediction mode is determined from the plurality of remaining mode candidates when the specific reference line candidate is identical to the first one of the plurality of reference line candidates and the mpm flag is different from the predefined value, and the first one of the plurality of reference line candidates is immediately adjacent to the block unit; determining the intra prediction mode of the block unit based on a first one of a plurality of mode indices, when the intra prediction mode is selected from the plurality of most probable modes, wherein the first one of the plurality of mode indices is an mpm index; determining the intra prediction mode of the block unit based on a second one of the plurality of mode indices, when the intra prediction mode is selected from the plurality of remaining mode candidates; and reconstructing the block unit of the image frame based on the intra prediction mode. a plurality of most probable modes is selected from a plurality of intra mode candidates, a plurality of remaining mode candidates is generated by removing the plurality of most probable modes from a plurality of intra mode candidates, the intra prediction mode is determined, without parsing the mpm flag, from the plurality of most probable modes when the specific reference line candidate is different from a first one of a plurality of reference line candidates; the intra prediction mode is determined from the plurality of most probable modes when the specific reference line candidate is identical to the first one of the plurality of reference line candidates and the mpm flag is equal to a predefined value, the intra prediction mode is determined from the plurality of remaining mode candidates when the specific reference line candidate is identical to the first one of the plurality of reference line candidates and the mpm flag is different from the predefined value, and the first one of the plurality of reference line candidates is immediately adjacent to the block unit; determining the intra prediction mode of the block unit based on a first one of a plurality of mode indices, when the intra prediction mode is selected from the plurality of most probable modes, wherein the first one of the plurality of mode indices is an mpm index; determining the intra prediction mode of the block unit based on a second one of the plurality of mode indices, when the intra prediction mode is selected from the plurality of remaining mode candidates; and reconstructing the block unit of the image frame based on the intra prediction mode.