One processing section 131 executes a process of generating image data K representing a black image on the basis of the image data Y, M, and C, and sequentially executes a process of removing elements of the black image contained in the image data Y, from the image data Y, a process of removing the elements of the black image contained in the image data M, from the image data M, and a process of removing the elements of the black image contained in the image data C, from the image data C.