In this paper, the theory of inter-reflections between "diffuse + specular" surfaces is represented by equations. The lighting calculation equations were led from a study of O'Brien, and the rendering equations were led from a study of Matsuura. In the field of computer graphics a study of Wallace, which is similar to this paper, is already published. But equations shown by him are vague and don't correctly represent physical phenomena. All equations in this paper are derived from physically correct theories.
