We propose a simple technique for the efficient estimation of the similarity of light transport paths. Considering descriptors of the incident radiance, we improve both filtering [Keller et al. 2014] and caching based [Ward et al. 1988] variance reduction techniques for image synthesis that so far could not measure variations of material and lighting as they only included geometric measures of similarity, such as the divergence of normals, irradiance gradients, and the distance between vertices storing information.
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