First photographed images taken at a plurality of angles and brightness information of each of the first photographed images are obtained. According to the brightness information of each of the colors, a relational model is established. Second photographed images taken at a plurality of angles and brightness distribution information of each of the second photographed images are obtained. The brightness distribution information is corrected based on the relational model. Measured brightness values are obtained, and gray level correction values for a preset gray level is calculated. Color deviation is corrected based on the gray level correction values.