Method and device for predicting block on basis of illumination compensation in image coding system

A block prediction method, which is performed by a decoding apparatus, the method comprising:

• deriving a reference block from a reference picture to predict a current block in a current picture;
• determining reference illumination compensation (IC) parameters;
• generating an illumination-compensated reference block by applying reference IC to the reference block based on the reference IC parameters;
• and
• generating prediction samples of the current block based on the illumination-compensated reference block,
• wherein the reference IC parameters comprise parameters a and b, and at least one of the parameters a and b is calculated based on first neighboring samples of the reference block and second neighboring samples of the current block,
• wherein the first neighboring samples comprise first left neighboring samples and first upper neighboring samples of the reference block, and the second neighboring samples comprise second left neighboring samples and second upper neighboring samples of the current block, and
• wherein odd- or even-numbered samples among the first left neighboring samples, first upper neighboring samples, second left neighboring samples, and second upper neighboring samples are used to calculate at least one of the parameters a and b.