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Now showing 1 - 6 of 6
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    Improved Half Vector Space Light Transport
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Hanika, Johannes; Kaplanyan, Anton; Dachsbacher, Carsten; Jaakko Lehtinen and Derek Nowrouzezahrai
    In this paper, we present improvements to half vector space light transport (HSLT) [KHD14], which make this approach more practical, robust for difficult input geometry, and faster. Our first contribution is the computation of half vector space ray differentials in a different domain than the original work. This enables a more uniform stratification over the image plane during Markov chain exploration. Furthermore, we introduce a new multi chain perturbation in half vector space, which, if combined appropriately with half vector perturbation, makes the mutation strategy both more robust to geometric configurations with fine displacements and faster due to reduced number of ray casts. We provide and analyze the results of improved HSLT and discuss possible applications of our new half vector ray differentials.
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    Physically Meaningful Rendering using Tristimulus Colours
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Meng, Johannes; Simon, Florian; Hanika, Johannes; Dachsbacher, Carsten; Jaakko Lehtinen and Derek Nowrouzezahrai
    In photorealistic image synthesis the radiative transfer equation is often not solved by simulating every wavelength of light, but instead by computing tristimulus transport, for instance using sRGB primaries as a basis. This choice is convenient, because input texture data is usually stored in RGB colour spaces. However, there are problems with this approach which are often overlooked or ignored. By comparing to spectral reference renderings, we show how rendering in tristimulus colour spaces introduces colour shifts in indirect light, violation of energy conservation, and unexpected behaviour in participating media. Furthermore, we introduce a fast method to compute spectra from almost any given XYZ input colour. It creates spectra that match the input colour precisely. Additionally, like in natural reflectance spectra, their energy is smoothly distributed over wide wavelength bands. This method is both useful to upsample RGB input data when spectral transport is used and as an intermediate step for corrected tristimulus-based transport. Finally, we show how energy conservation can be enforced in RGB by mapping colours to valid reflectances.
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    Real‐Time Isosurface Extraction With View‐Dependent Level of Detail and Applications
    (Copyright © 2015 The Eurographics Association and John Wiley & Sons Ltd., 2015) Scholz, Manuel; Bender, Jan; Dachsbacher, Carsten; Deussen, Oliver and Zhang, Hao (Richard)
    Volumetric scalar data sets are common in many scientific, engineering and medical applications where they originate from measurements or simulations. Furthermore, they can represent geometric scene content, e.g. as distance or density fields. Often isosurfaces are extracted, either for indirect volume visualization in the former category, or to simply obtain a polygonal representation in case of the latter. However, even moderately sized volume data sets can result in complex isosurfaces which are challenging to recompute in real time, e.g. when the user modifies the isovalue or when the data itself are dynamic. In this paper, we present a GPU‐friendly algorithm for the extraction of isosurfaces, which provides adaptive level of detail rendering with view‐dependent tessellation. It is based on a longest edge bisection scheme where the resulting tetrahedral cells are subdivided into four hexahedra, which then form the domain for the subsequent isosurface extraction step. Our algorithm generates meshes with good triangle quality even for highly non‐linear scalar data. In contrast to previous methods, it does not require any stitching between regions of different levels of detail. As all computation is performed at run time and no pre‐processing is required, the algorithm naturally supports dynamic data and allows us to change isovalues at any time.Volumetric scalar data sets are common in many scientific, engineering and medical applications where they originate from measurements or simulations. Furthermore, they can represent geometric scene content, e.g. as distance or density fields. Often isosurfaces are extracted, either for indirect volume visualization in the former category, or to simply obtain a polygonal representation in case of the latter. However, even moderately sized volume data sets can result in complex isosurfaces which are challenging to recompute in real time, e.g. when the user modifies the isovalue or when the data itself are dynamic.
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    Visualization of Coherent Structures of Light Transport
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Zirr, Tobias; Ament, Marco; Dachsbacher, Carsten; H. Carr, K.-L. Ma, and G. Santucci
    Inspired by vector field topology, an established tool for the extraction and identification of important features of flows and vector fields, we develop means for the analysis of the structure of light transport. For that, we derive an analogy to vector field topology that defines coherent structures in light transport. We also introduce Finite-Time Path Deflection (FTPD), a scalar quantity that represents the deflection characteristic of all light transport paths passing through a given point in space. For virtual scenes, the FTPD can be computed directly using path-space Monte Carlo integration. We visualize the FTPD field for several example scenes and discuss the revealed structures. Lastly, we show that the coherent regions visualized by the FTPD are closely related to the coherent regions in our new topologically-motivated analysis of light transport. FTPD visualizations are thus also visualizations of the structure of light transport.
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    Rich-VPLs for Improving the Versatility of Many-Light Methods
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Simon, Florian; Hanika, Johannes; Dachsbacher, Carsten; Olga Sorkine-Hornung and Michael Wimmer
    Many-light methods approximate the light transport in a scene by computing the direct illumination from many virtual point light sources (VPLs), and render low-noise images covering a wide range of performance and quality goals. However, they are very inefficient at representing glossy light transport. This is because a VPL on a glossy surface illuminates a small fraction of the scene only, and a tremendous number of VPLs might be necessary to render acceptable images. In this paper, we introduce Rich-VPLs which, in contrast to standard VPLs, represent a multitude of light paths and thus have a more widespread emission profile on glossy surfaces and in scenes with multiple primary light sources. By this, a single Rich-VPL contributes to larger portions of a scene with negligible additional shading cost. Our second contribution is a placement strategy for (Rich-)VPLs proportional to sensor importance times radiance. Although both Rich-VPLs and improved placement can be used individually, they complement each other ideally and share interim computation. Furthermore, both complement existing manylight methods, e.g. Lightcuts or the Virtual Spherical Lights method, and can improve their efficiency as well as their application for scenes with glossy materials and many primary light sources.
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    Stochastic Soft Shadow Mapping
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Liktor, Gabor; Spassov, Stanislav; Mückl, Gregor; Dachsbacher, Carsten; Jaakko Lehtinen and Derek Nowrouzezahrai
    In this paper, we extend the concept of pre-filtered shadow mapping to stochastic rasterization, enabling real-time rendering of soft shadows from planar area lights. Most existing soft shadow mapping methods lose important visibility information by relying on pinhole renderings from an area light source, providing plausible results only for small light sources. Since we sample the entire 4D shadow light field stochastically, we are able to closely approximate shadows of large area lights as well. In order to efficiently reconstruct smooth shadows from this sparse data, we exploit the analogy of soft shadow computation to rendering defocus blur, and introduce a multiplane pre-filtering algorithm. We demonstrate how existing pre-filterable approximations of the visibility function, such as variance shadow mapping, can be extended to four dimensions within our framework.