An image processing device comprises a first input unit configured to input first information indicating a fine irregularity of a surface of a body to be rendered; a generation unit configured to generate, as pieces of information each indicating a tilt of a surface of an object to be rendered, pieces of second information for respective wavelengths from the first information; a rendering unit configured to render objects for the respective wavelengths based on the pieces of second information for the respective wavelengths; and a combining unit configured to generate an image of the body to be rendered by combining the objects for the respective wavelengths.