The present invention relates to a method for encoding and decoding images, wherein, if bi-prediction is applied, a weight for a merge candidate is derived, thereby improving the image compression efficiency, and making it possible to efficiently configure a motion vector candidate. A merge candidate list of the current block is produced on the basis of inter-prediction information, and the candidate includes a configured affine merge candidate. If the configured affine merge candidate is produced on the basis of a combination of control points including CP0, weight index information regarding the configured affine merge candidate is produced on the basis of weight index information regarding CP0. If the configured affine merge candidate is produced on the basis of a combination of control points excluding CP0, weight index information regarding the configured affine merge candidate is derived on the basis of weight index information regarding CP1.