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Figure 1: Wavelength-dependent subsurface scattering with single wavelength sampling (left) and our proposed method (right). The lower image halves are rendered with 4 paths per pixel, and the upper halves are rendered with 1024. For both sample counts, the hero wavelength images took only 3.5% longer than the single wavelength ones. AbstractWe present a spectral rendering technique that offers a compelling set of advantages over existing approaches.The key idea is to propagate energy along paths for a small, constant number of changing wavelengths. The first of these, the hero wavelength, is randomly sampled for each path, and all directional sampling is solely based on it. The additional wavelengths are placed at equal distances from the hero wavelength, so that all path wavelengths together always evenly cover the visible range. A related technique, spectral multiple importance sampling, was already introduced a few years ago. We propose a simplified and optimised version of this approach which is easier to implement, has good performance characteristics, and is actually more powerful than the original method. Our proposed method is also superior to techniques which use a static spectral representation, as it does not suffer from any inherent representation bias. We demonstrate the performance of our method in several application areas that are of critical importance for production work, such as fidelity of colour reproduction, sub-surface scattering, dispersion and volumetric effects. We also discuss how to couple our proposed approach with several technologies that are important in current production systems, such as photon maps, bidirectional path tracing, environment maps, and participating media.

In this paper we derive the complete set of formulas which is needed to generate physically plausible images of uniaxial crystals. So far no computer graphics publication contains all the formulas one needs to compute the interaction of light with such crystals in a form that is useable by a graphics application, especially if a polarisation-aware rendering system is being used. This paper contains the complete derivation of the Fresnel coefficients for birefringent transparent materials, as well as for the direction cosines of the extraordinary ray and the Mueller matrices necessary to describe polarisation effects. The formulas we derive can be directly used in a ray based renderer, and we demonstrate these capabilities in test scenes.

Figure 1: A synthetic image where our proposed BRDF model is used on a fluorescent orange surface that is being illuminated by several collimated monochrome light sources. The scene geometry is similar to that shown in figure 2. Note the colours of the directly viewed bright dots on the material itself, and the in some cases considerably different colours seen in the reflection patterns. It is noteworthy that the blue and green monochrome lights (second and third light from the left), which fall into the main area of the absorption curve shown in figure 4, exhibit the largest colour discrepancies between specular and diffuse reflection. AbstractFluorescence is an interesting and visually prominent effect, which has not been fully covered by Computer Graphics research so far.While the physical phenomenon of fluorescence has been addressed in isolation, the actual reflection behaviour of real fluorescent surfaces has never been documented, and no analytical BRDF models for such surfaces have been published yet.This paper aims to illustrate the reflection properties typical for diffuse fluorescent surfaces, and provides a BRDF model based on a layered microfacet approach that mimics them.