Estimation of Optimal Number of Rays in the Bidirectional Photon Mapping Method
The classic Monte-Carlo ray tracing is a powerful technique for simulating almost all effects in ray optics, but it may be prohibitively slow for, for example, calculation of images seen by a lens camera. Therefore, in practice there are often used its various modifications, in particular, bi-directional stochastic ray tracing with photon maps. The well-known flaw of all stochastic methods is their noise. The noise level, that is, the root mean square of pixel brightness calculated during given time, depends, besides all, on the number of rays traced from the light source and from the camera. The choice of the optimal parameters must provide the lowest noise level in a fixed time. This article is devoted to the choice of the optimal number of rays that minimizes the noise. It is proved that this minimal noise is in the same time homogeneous over the image. We produce the formulae to calculate the optimal number of rays from several coefficients which can be obtained from a bi-directional ray tracing of several auxiliary variants. It happens that this optimum is rather wide i.e. the noise level changes with the number of rays slowly, which allows to choose it including other factors e.g. limit this number to save memory.
realistic rendering, bi-directional Monte-Carlo ray tracing, photon maps, denoising
Язык публикации: английский, страниц:12 (с. 24-35)