So I was thinking about the problem of shadows in images. From an image processing point of view, would you classify cast shadows in a scene as an additive phenomenon or as a multiplicative phenomenon on top of the shading?
From what I can understand, for the case of non-lambertian image formation equation, the specularity is formulated as additive because it is dependent on the view direction. But for the case of shadows, is there any similarity to that? Or should shadows be formulated as just as a scaling term over the shading?
Any views or pointing towards proper papers or materials would be highly appreciated. Thanks!