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Item 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 NowrouzezahraiIn 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.Item Memory-Efficient On-The-Fly Voxelization of Particle Data(The Eurographics Association, 2015) Zirr, Tobias; Dachsbacher, Carsten; C. Dachsbacher and P. NavrátilIn this paper we present a novel GPU-friendly real-time voxelization technique for rendering homogeneous media that is defined by particles, e.g. fluids obtained from particle-based simulations such as Smoothed Particle Hydrodynamics (SPH). Our method computes view-adaptive binary voxelizations with on-the-fly compression of a tiled perspective voxel grid, achieving higher resolutions than previous approaches. It allows for interactive generation of realistic images, enabling advanced rendering techniques such as ray casting-based refraction and reflection, light scattering and absorption, and ambient occlusion. In contrast to previous methods, it does not rely on preprocessing such as expensive, and often coarse, scalar field conversion or mesh generation steps. Our method directly takes unsorted particle data as input. It can be further accelerated by identifying fully populated simulation cells during simulation. The extracted surface can be filtered to achieve smooth surface appearance.Item Frontmatter: EG PGV 2015 - Eurographics Symposium on Parallel Graphics and Visualization(Eurographics Association, 2015) Dachsbacher, Carsten; Navrátil, Paul; -Item Low‐Cost Subpixel Rendering for Diverse Displays(The Eurographics Association and John Wiley and Sons Ltd., 2014) Engelhardt, Thomas; Schmidt, Thorsten‐Walther; Kautz, Jan; Dachsbacher, Carsten; Holly Rushmeier and Oliver DeussenSubpixel rendering increases the apparent display resolution by taking into account the subpixel structure of a given display. In essence, each subpixel is addressed individually, allowing the underlying signal to be sampled more densely. Unfortunately, naïve subpixel sampling introduces colour aliasing, as each subpixel only displays a specific colour (usually R, G and B subpixels are used). As previous work has shown, chromatic aliasing can be reduced significantly by taking the sensitivity of the human visual system into account. In this work, we find optimal filters for subpixel rendering for a diverse set of 1D and 2D subpixel layout patterns. We demonstrate that these optimal filters can be approximated well with analytical functions. We incorporate our filters into GPU‐based multi‐sample anti‐aliasing to yield subpixel rendering at a very low cost (1–2 ms filtering time at HD resolution). We also show that texture filtering can be adapted to perform efficient subpixel rendering. Finally, we analyse the findings of a user study we performed, which underpins the increased visual fidelity that can be achieved for diverse display layouts, by using our optimal filters.Subpixel rendering increases the apparent display resolution by taking into account the subpixel structure of a given display. In essence, each subpixel is addressed individually, allowing the underlying signal to be sampled more densely. Unfortunately, naïve subpixel sampling introduces colour aliasing, as each subpixel only displays a specific colour (usually R, G, and B subpixels are used). As previous work has shown, chromatic aliasing can be reduced significantly by taking the sensitivity of the human visual system into account. In this work, wefind optimal filters for subpixel rendering for a diverse set of 1D and 2D subpixel layout patterns.Item Level of Detail for Real-Time Volumetric Terrain Rendering(The Eurographics Association, 2013) Scholz, Manuel; Bender, Jan; Dachsbacher, Carsten; Michael Bronstein and Jean Favre and Kai HormannTerrain rendering is an important component of many GIS applications and simulators. Most methods rely on heightmap-based terrain which is simple to acquire and handle, but has limited capabilities for modeling features like caves, steep cliffs, or overhangs. In contrast, volumetric terrain models, e.g. based on isosurfaces can represent arbitrary topology. In this paper, we present a fast, practical and GPU-friendly level of detail algorithm for large scale volumetric terrain that is specifically designed for real-time rendering applications. Our algorithm is based on a longest edge bisection (LEB) scheme. The resulting tetrahedral cells are subdivided into four hexahedra, which form the domain for a subsequent isosurface extraction step. The algorithm can be used with arbitrary volumetric models such as signed distance fields, which can be generated from triangle meshes or discrete volume data sets. In contrast to previous methods our algorithm does not require any stitching between detail levels. It generates crack free surfaces with a good triangle quality. Furthermore, we efficiently extract the geometry at runtime and require no preprocessing, which allows us to render infinite procedural content with low memory consumption.Item Selective Inspection and Interactive Visualization of Light Transport in Virtual Scenes(The Eurographics Association and John Wiley and Sons Ltd., 2012) Reiner, Tim; Kaplanyan, Anton; Reinhard, Marcel; Dachsbacher, Carsten; P. Cignoni and T. ErtlThis paper presents novel interactive visualization techniques for inspecting the global light transport in virtual scenes. First, we propose a simple extension to photon mapping to gather required lighting information. We then introduce a set of five light inspection tools which process this data to provide further insights. Corresponding visualizations help the user to comprehend how light travels within a scene, how the lighting affects the appearance of a surface, and how objects cause lighting effects such as caustics. We implemented all tools for direct usage in real production environments. Rendering is based on progressive photon mapping, providing interactivity and immediate visual feedback. We conducted a user study to evaluate all techniques in various application scenarios and hence discuss their individual strengths and weaknesses. Moreover, we present feedback from domain experts.Item Interactive Appearance Editing in RGB-D Images(The Eurographics Association, 2014) Bergmann, Stephan; Ritschel, Tobias; Dachsbacher, Carsten; Jan Bender and Arjan Kuijper and Tatiana von Landesberger and Holger Theisel and Philipp UrbanThe availability of increasingly powerful and affordable image and depth sensors in conjunction with the necessary processing power creates novel possibilities for more sophisticated and powerful image editing tools. Along these lines we present a method to alter the appearance of objects in RGB-D images by re-shading their surfaces with arbitrary BRDF models and subsurface scattering using the dipole diffusion approximation. To evaluate the incident light for re-shading we combine ray marching using the depth buffer as approximate geometry and environment lighting. The environment map is built from information solely contained in the RGB-D input image exploiting both the reflections on glossy surfaces as well as geometric information. Our CPU/GPU implementation provides interactive feedback to facilitate intuitive editing.We compare and demonstrate our method with rendered images and digital photographs.Item Coherent Culling and Shading for Large Molecular Dynamics Visualization(The Eurographics Association and Blackwell Publishing Ltd., 2010) Grottel, Sebastian; Reina, Guido; Dachsbacher, Carsten; Ertl, Thomas; G. Melancon, T. Munzner, and D. WeiskopfMolecular dynamics simulations are a principal tool for studying molecular systems. Such simulations are used to investigate molecular structure, dynamics, and thermodynamical properties, as well as a replacement for, or complement to, costly and dangerous experiments. With the increasing availability of computational power the resulting data sets are becoming increasingly larger, and benchmarks indicate that the interactive visualization on desktop computers poses a challenge when rendering substantially more than millions of glyphs. Trading visual quality for rendering performance is a common approach when interactivity has to be guaranteed. In this paper we address both problems and present a method for high-quality visualization of massive molecular dynamics data sets. We employ several optimization strategies on different levels of granularity, such as data quantization, data caching in video memory, and a two-level occlusion culling strategy: coarse culling via hardware occlusion queries and a vertex-level culling using maximum depth mipmaps. To ensure optimal image quality we employ GPU raycasting and deferred shading with smooth normal vector generation. We demonstrate that our method allows us to interactively render data sets containing tens of millions of high-quality glyphs.Item Efficient Monte Carlo Rendering with Realistic Lenses(The Eurographics Association and John Wiley and Sons Ltd., 2014) Hanika, Johannes; Dachsbacher, Carsten; B. Levy and J. KautzIn this paper we present a novel approach to simulate image formation for a wide range of real world lenses in the Monte Carlo ray tracing framework. Our approach sidesteps the overhead of tracing rays through a system of lenses and requires no tabulation. To this end we first improve the precision of polynomial optics to closely match ground-truth ray tracing. Second, we show how the Jacobian of the optical system enables efficient importance sampling, which is crucial for difficult paths such as sampling the aperture which is hidden behind lenses on both sides. Our results show that this yields converged images significantly faster than previous methods and accurately renders complex lens systems with negligible overhead compared to simple models, e.g. the thin lens model. We demonstrate the practicality of our method by incorporating it into a bidirectional path tracing framework and show how it can provide information needed for sophisticated light transport algorithms.Item 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 NowrouzezahraiIn 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.