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28 May 2018 Realistic image synthesis in presence of birefrigent media by backward ray tracing technique
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We describe an algorithm of tracing a backward (from camera) ray in a scene which contains birefrigent (uniaxial) media. The physics of scattering of an electromagnetic wave by a boundary between two media is well known and is a base for ray tracing algorithms; but processing of a backward ray differs from scattering of a “natural” forward ray. Say, when a backward ray refracts by a boundary, besides the energy transfer coefficient like for a forward ray one must account for the luminance change due to beam divergence. We calculate this factor and prove it must be evaluated only for the first and the last media along the ray path while the contributions from the intermediate media mutually cancel. In this paper we present a closed numerical method that allows to perform transformation of a backward ray on a boundary between two media either of which can be birefrigent. We hope it is more convenient and ready for usage in ray tracing engines that known publications. Calculation utilizes Helmholtz reciprocity to calculate directions of scattered rays and their polarization (i.e. Mueller matrices) which is advantageous over a straightforward “reverse” of forward ray transformation. The algorithm was integrated in the lighting simulation system Lumicept and allowed for an efficient calculation of images of scenes with crystal elements.
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Dmitry Zhdanov, Sergey Ershov, Leo Shapiro, Vadim Sokolov, Alexey Voloboy, Vladimir Galaktionov, and Igor Potemin "Realistic image synthesis in presence of birefrigent media by backward ray tracing technique", Proc. SPIE 10694, Computational Optics II, 106940D (28 May 2018);

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