EGSR14: 25th Eurographics Symposium on Rendering
https://diglib.eg.org:443/handle/10.2312/14331
2024-03-28T08:52:49Z
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Probabilistic Visibility Evaluation using Geometry Proxies
https://diglib.eg.org:443/handle/10.1111/v33i4pp143-152
Probabilistic Visibility Evaluation using Geometry Proxies
Billen, Niels; Lagae, Ares; Dutré, Philip
Wojciech Jarosz and Pieter Peers
Evaluating the visibility between two points is a fundamental problem for ray-tracing and path-tracing algorithms. Ideally, visibility computations are organized such that a minimum number of geometric primitives need to be checked for each ray. Replacing complex geometric shapes by a simpler set of primitives is one strategy to control the amount of intersection calculations. However, approximating the original geometry introduces inaccuracies in e.g. shadow regions when shadow rays are intersected with the approximate geometry. This paper presents a theoretical framework for probabilistic visibility evaluation. When intersecting a shadow ray with the scene, we randomly select the original geometry, the approximated geometry, or one of several correction terms, to be tested. Not all shadow rays will therefore intersect the original geometry, but our method is able to produce unbiased images that converge to the correct solution. Although probabilistic visibility evaluation is an experimental idea, we show several example scenes that highlight the potential for future improvements.
2014-01-01T00:00:00Z
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A Physically-Based BSDF for Modeling the Appearance of Paper
https://diglib.eg.org:443/handle/10.1111/v33i4pp133-142
A Physically-Based BSDF for Modeling the Appearance of Paper
Papas, Marios; Mesa, Krystle de; Jensen, Henrik Wann
Wojciech Jarosz and Pieter Peers
We present a novel appearance model for paper. Based on our appearance measurements for matte and glossy paper, we find that paper exhibits a combination of subsurface scattering, specular reflection, retroreflection, and surface sheen. Classic microfacet and simple diffuse reflection models cannot simulate the double-sided appearance of a thin layer. Our novel BSDF model matches our measurements for paper and accounts for both reflection and transmission properties. At the core of the BSDF model is a method for converting a multi-layer subsurface scattering model (BSSRDF) into a BSDF, which allows us to retain physically-based absorption and scattering parameters obtained from the measurements. We also introduce a method for computing the amount of light available for subsurface scattering due to transmission through a rough dielectric surface. Our final model accounts for multiple scattering, single scattering, and surface reflection and is capable of rendering paper with varying levels of roughness and glossiness on both sides.
2014-01-01T00:00:00Z
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Hero Wavelength Spectral Sampling
https://diglib.eg.org:443/handle/10.1111/v33i4pp123-131
Hero Wavelength Spectral Sampling
Wilkie, Alexander; Nawaz, Sehera; Droske, Marc; Weidlich, Andrea; Hanika, Johannes
Wojciech Jarosz and Pieter Peers
We 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.
2014-01-01T00:00:00Z
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Spectral Ray Differentials
https://diglib.eg.org:443/handle/10.1111/v33i4pp113-122
Spectral Ray Differentials
Elek, Oskar; Bauszat, Pablo; Ritschel, Tobias; Magnor, Marcus; Seidel, Hans-Peter
Wojciech Jarosz and Pieter Peers
Light refracted by a dispersive interface leads to beautifully colored patterns that can be rendered faithfully with spectral Monte-Carlo methods. Regrettably, results often suffer from chromatic noise or banding, requiring high sampling rates and large amounts of memory compared to renderers operating in some trichromatic color space. Addressing this issue, we introduce spectral ray differentials, which describe the change of light direction with respect to changes in the spectrum. In analogy with the classic ray and photon differentials, this information can be used for filtering in the spectral domain. Effectiveness of our approach is demonstrated by filtering for offline spectral light and path tracing as well as for an interactive GPU photon mapper based on splatting. Our results show considerably less chromatic noise and spatial aliasing while retaining good visual similarity to reference solutions with negligible overhead in the order of milliseconds.
2014-01-01T00:00:00Z