If the optical constants of embedded pigments and host material differ from each other, light waves travelling through the medium are scattered and absorbed. In order to perform ray-tracing computations one must know the probability/distance for scattering and absorption events. In addition, the angle distribution of the scattered light must be taken into account when the new direction of a scattered ray is computed.

In the case of spheres embedded in a homogeneous host material the problem is solved by the so-called Mie theory. The SPRAY software contains a module that performs Mie computations for user-defined size distributions of spheres. The spheres may have multiple coatings.

In the following the scattering and absorption properties of the demo pigments are given: