Method and device for video decoding, and method and device for video encoding

A video decoding method comprising:

• determining whether a current luma block is in contact with an upper boundary of a largest coding unit including the current luma block;
• when it is determined that the current luma block is in contact with the upper boundary of the largest coding unit, determining an upper reference line of the current luma block as one reference line;
• when it is determined that the current luma block is not in contact with the upper boundary of the largest coding unit, determining the upper reference line of the current luma block as two reference lines;
• and
• performing prediction on a current chroma block corresponding to the current luma block, based on the determined upper reference line.

A video encoding method comprising:

• determining whether a current block is in contact with an upper boundary of a largest coding unit including the current block;
• when it is determined that the current block is in contact with the upper boundary of the largest coding unit, determining an upper reference line of the current block as one reference line;
• when it is determined that the current block is not in contact with the upper boundary of the largest coding unit, determining the upper reference line of the current block based on N reference lines;
• and
• performing prediction on the current block, based on the determined upper reference line,
• wherein N is a natural number.