We present a new importance sampling technique for stochastic ray-based global illumination methods. It allows to enhance the efficiency of global illumination calculations in general scenes with complex illumination settings by selecting preferably those sampling or shooting directions which yield a high contribution. The probability density functions for this are generated with a photon map or importance map that represents the expected contribution. An outgoing direction for a given point in the scene is selected by making directional footprints of the nearest neighbor particles onto the hemisphere above the point. By selecting the radii of the footprints adaptively according to the directional density of the particles, rays can be shot precisely into highly contributing regions where several particles come from a small solid angle. We compare our new technique with existing importance sampling techniques in photon map global illumination simulation, and show that our new technique achieves a considerably lower level of noise in the same computation time.
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