An image encoding/decoding method and apparatus are disclosed. The method of decoding an image according to the present invention, comprises, generating a first prediction block of a current block, generating a second prediction block of the current block and generating a final prediction sample of the current block using a sample unit weighted sum of the first prediction block and the second prediction block, wherein a weight used for the sample unit weighted sum is determined based on a location of a current luma sample and a geometric prediction mode (GPM) boundary line for partitioning the current block.