A fast rendering method for a scene with participating media of anisotropic scattering property

This paper presents an efficient technique for global illumination rendering of a scene with participating media. The rendering handling participating media is performed by ray marching method, which requires sampling along each view direction. The step size of the ray marching must be taken short to generate a high quality image and thus leads to very long computational time. One possible method to improve the computational cost is to exploit importance sampling. In this paper, we propose a method to determine the step size based on the importance sampling technique. For efficient sampling, the probability density function which is "close" to the radiance distribution is required. In our method, 3D space is divided into a set of uniform grids. The radiance distribution is approximated using the grid structure. To deal with the participating media which has anisotropic scattering property, we use spherical harmonics to represent directional dependence of radiance distribution. Using this grid-based representation, fast calculation of good approximation of desirable probability density is made possible. Using this probability, high quality image can be rendered with fewer number of sampling compared to the conventional methods.