Monte Carlo Rendering with Natural Illumination

We present a new sampling technique for using environment maps for illumination in a Monte Carlo ray tracer, based on directly importance sampling the continuous two-dimensional distribution of illumination as a function of direction. Unlike previous techniques for high-quality rendering with environment maps, our method requires very little precomputation, is easy to implement, and is compatible with existing approaches for Monte Carlo variance reduction. We achieve equivalent or lower error in rendered images than previous methods and robustly handle a wider variety of reflection models for the same amount of rendering time, though our technique uses three orders of magnitude less precomputation. For interactive rendering, our sampling methods can be used to generate a set of directional light sources that accurately approximate the environment map’s illumination in a few hundredths of a second.