Method and apparatus for encoding or decoding image using syntax signaling for adaptive weight prediction

An image encoding method comprising:

• determining a first motion vector and a second motion vector indicating a first correspondence region and a second correspondence region which are most similar to a current block in a first reference picture and a second reference picture;
• confirming whether to perform weighted bi-prediction based on the first correspondence region and the second correspondence region;
• when it is confirmed that the bi-prediction is to be performed, performing the weighted bi-prediction of a block unit or a pixel unit on the current block by using the first motion vector, the second motion vector, and a weight value;
• and
• adding additional syntax elements to an encoded bitstream, the additional syntax elements including a prefix indicating a number of additional syntax elements and information indicating whether to perform the weighted bi-prediction on the current block.