Estimation of noise in calculation of scattering medium luminance by MCRT

We investigate new method for calculation of radiance of scattering medium by bi-directional Monte-Carlo ray tracing with photon maps. Usually photons are collected by an integration spheres at the ends of camera ray segments, or a cylinder along that segments. Meanwhile in our method several integration spheres are distributed at random along the first camera ray segment. The rest segments do not collecting photons. The method optimal for a particular scene is the one which produces the least noise, so one need to be able to estimate it. In this paper an analytic calculation of noise in the general bi-directional Monte-Carlo ray tracing is derived and then applied to the proposed method. Then the analytic estimates of noise can be used to find optimal parameters and/or to choose between single integration sphere, multiple integration spheres and integration cylinders.