36-Issue 4

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https://diglib.eg.org/handle/10.2312/2631440

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Browsing 36-Issue 4 by Subject "Color"

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    Multiple Axis-Aligned Filters for Rendering of Combined Distribution Effects
    (The Eurographics Association and John Wiley & Sons Ltd., 2017) Wu, Lifan; Yan, Ling-Qi; Kuznetsov, Alexandr; Ramamoorthi, Ravi; Zwicker, Matthias and Sander, Pedro
    Distribution effects such as diffuse global illumination, soft shadows and depth of field, are most accurately rendered using Monte Carlo ray or path tracing. However, physically accurate algorithms can take hours to converge to a noise-free image. A recent body of work has begun to bridge this gap, showing that both individual and multiple effects can be achieved accurately and efficiently. These methods use sparse sampling, GPU raytracers, and adaptive filtering for reconstruction. They are based on a Fourier analysis, which models distribution effects as a wedge in the frequency domain. The wedge can be approximated as a single large axis-aligned filter, which is fast but retains a large area outside the wedge, and therefore requires a higher sampling rate; or a tighter sheared filter, which is slow to compute. The state-of-the-art fast sheared filtering method combines low sampling rate and efficient filtering, but has been demonstrated for individual distribution effects only, and is limited by high-dimensional data storage and processing. We present a novel filter for efficient rendering of combined effects, involving soft shadows and depth of field, with global (diffuse indirect) illumination. We approximate the wedge spectrum with multiple axis-aligned filters, marrying the speed of axis-aligned filtering with an even more accurate (compact and tighter) representation than sheared filtering. We demonstrate rendering of single effects at comparable sampling and frame-rates to fast sheared filtering. Our main practical contribution is in rendering multiple distribution effects, which have not even been demonstrated accurately with sheared filtering. For this case, we present an average speedup of 6 compared with previous axis-aligned filtering methods.
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    Real-Time Linear BRDF MIP-Mapping
    (The Eurographics Association and John Wiley & Sons Ltd., 2017) Xu, Chao; Wang, Rui; Zhao, Shuang; Bao, Hujun; Zwicker, Matthias and Sander, Pedro
    We present a new technique to jointly MIP-map BRDF and normal maps. Starting with generating an instant BRDF map, our technique builds its MIP-mapped versions based on a highly efficient algorithm that interpolates von Mises-Fisher (vMF) distributions. In our BRDF MIP-maps, each pixel stores a vMF mixture approximating the average of all BRDF lobes from the finest level. Our method is capable of jointly MIP-mapping BRDF and normal maps, even with high-frequency variations, at real-time while preserving high-quality reflectance details. Further, it is very fast, easy to implement, and requires no precomputation.