An image processing apparatus configured to perform an appropriate blurring processing in which a height difference in the surface shape with fine unevenness is taken into consideration, and to reproduce the surface shape faithfully corresponding to an original image. The image processing apparatus for generating computer graphics expressing an object includes a first acquisition unit configured to acquire height information representing a relative height difference in a surface of the object, a second acquisition unit configured to acquire at least one scattering function representing an internal scattering characteristic of light in the object, and a calculation unit configured to calculate a luminance value of the object based on the height information and the scattering function.