A first obtaining unit obtains two images obtained by capturing images of an inspection target object under different capturing environments with different illumination conditions inputted by a user. A second obtaining unit obtains area information that specifies two types of areas set by the user regarding an area in each image. The two types of areas include a reference area serving as a reference for comparison between the areas and a comparison target area serving as a target of comparison. A converting unit generates color conversion parameters for carrying out color conversion such that a color value of the reference area in one image coincides with a color value of the reference area in the other image. A deriving unit derives a color difference between the reference area and the comparison target area regarding each of the two images.