Search Results

Now showing 1 - 10 of 15
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    Guiding Light Trees for Many-Light Direct Illumination
    (The Eurographics Association, 2023) Hamann, Eric; Jung, Alisa; Dachsbacher, Carsten; Babaei, Vahid; Skouras, Melina
    Path guiding techniques reduce the variance in path tracing by reusing knowledge from previous samples to build adaptive sampling distributions. The Practical Path Guiding (PPG) approach stores and iteratively refines an approximation of the incident radiance field in a spatio-directional data structure that allows sampling the incident radiance. However, due to the limited resolution in both spatial and directional dimensions, this discrete approximation is not able to accurately capture a large number of very small lights. We present an emitter sampling technique to guide next event estimation (NEE) with a global light tree and adaptive tree cuts that integrates into the PPG framework. In scenes with many lights our technique significantly reduces the RMSE compared to PPG with uniform NEE, while adding close to no overhead in scenes with few light sources. The results show that our technique can also aid the incident radiance learning of PPG in scenes with difficult visibility.
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    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. Ertl
    This 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.
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    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. Kautz
    In 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.
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    State of the Art in Artistic Editing of Appearance, Lighting, and Material
    (The Eurographics Association, 2014) Schmidt, Thorsten-Walther; Pellacini, Fabio; Nowrouzezahrai, Derek; Jarosz, Wojciech; Dachsbacher, Carsten; Sylvain Lefebvre and Michela Spagnuolo
    Mimicking the appearance of the real world is a longstanding goal of computer graphics, with several important applications in the feature-film, architecture and medical industries. Images with well-designed shading are an important tool for conveying information about the world, be it the shape and function of a CAD model, or the mood of a movie sequence. However, authoring this content is often a tedious task, even if undertaken by groups of highly-trained and experienced artists. Unsurprisingly, numerous methods to facilitate and accelerate this appearance editing task have been proposed, enabling the editing of scene objects' appearances, lighting, and materials, as well as entailing the introduction of new interaction paradigms and specialized preview rendering techniques. In this STAR we provide a comprehensive survey of artistic appearance, lighting, and material editing approaches. We organize this complex and active research area in a structure tailored to academic researchers, graduate students, and industry professionals alike. In addition to editing approaches, we discuss how user interaction paradigms and rendering backends combine to form usable systems for appearance editing. We conclude with a discussion of open problems and challenges to motivate and guide future research.
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    Out-of-the-loop Autotuning of Metropolis Light Transport with Reciprocal Probability Binning
    (The Eurographics Association, 2023) Herveau, Killian; Otsu, Hisanari; Dachsbacher, Carsten; Babaei, Vahid; Skouras, Melina
    The performance of Markov Chain Monte Carlo (MCMC) rendering methods depends heavily on the mutation strategies and their parameters. We treat the underlying mutation strategies as black-boxes and focus on their parameters. This avoids the need for tedious manual parameter tuning and enables automatic adaptation to the actual scene. We propose a framework for out-of-the-loop autotuning of these parameters. As a pilot example, we demonstrate our tuning strategy for small-step mutations in Primary Sample Space Metropolis Light Transport. Our σ-binning strategy introduces a set of mutation parameters chosen by a heuristic: the inverse probability of the local direction sampling, which captures some characteristics of the local sampling. We show that our approach can successfully control the parameters and achieve better performance compared to non-adaptive mutation strategies.
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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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    Dual-Color Mixing for Fused Deposition Modeling Printers
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Reiner, Tim; Carr, Nathan; Mech, Radomir; Stava, Ondrej; Dachsbacher, Carsten; Miller, Gavin; B. Levy and J. Kautz
    In this work we detail a method that leverages the two color heads of recent low-end fused deposition modeling (FDM) 3D printers to produce continuous tone imagery. The challenge behind producing such two-tone imagery is how to finely interleave the two colors while minimizing the switching between print heads, making each color printed span as long and continuous as possible to avoid artifacts associated with printing short segments. The key insight behind our work is that by applying small geometric offsets, tone can be varied without the need to switch color print heads within a single layer. We can now effectively print (two-tone) texture mapped models capturing both geometric and color information in our output 3D prints.
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    Rasterized Bounding Volume Hierarchies
    (The Eurographics Association and John Wiley and Sons Ltd., 2012) Novák, Jan; Dachsbacher, Carsten; P. Cignoni and T. Ertl
    We present the rasterized bounding volume hierarchy (RBVH), a compact data structure that accelerates approximate ray casting of complex meshes and provides adjustable level of detail. During construction, we identify subtrees of BVHs containing surfaces that can be represented by height fields. For these subtrees the conventional ray-surface intersection, which possibly involves a large number of triangles, is replaced by a simple ray marching procedure to find the intersection with the surface. We describe GPU algorithms for construction, ray casting, and data querying of the RBVH that achieve comparable or higher performance than state of the art acceleration structures for triangle meshes. Moreover, RBVHs provide an inherent surface parameterization for storing data on the surfaces and natively handle triangle and point-based surface representations. We also show that RBVHs support adaptive level-of-detail and can be combined with traditional BVHs to handle complex scenes.
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    Adaptive Quantization Visibility Caching
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Popov, Stefan; Georgiev, Iliyan; Slusallek, Philipp; Dachsbacher, Carsten; I. Navazo, P. Poulin
    Ray tracing has become a viable alternative to rasterization for interactive applications and also forms the basis of most global illumination methods. However, even today's fastest ray-tracers offer only a tight budget of rays per pixel per frame. Rendering performance can be improved by increasing this budget, or by developing methods that use it more efficiently. In this paper we propose a global visibility caching algorithm that reduces the number of shadow rays required for shading to a fraction of less than 2% in some cases. We quantize the visibility function's domain while ensuring a minimal degradation of the final image quality. To control the introduced error, we adapt the quantization locally, accounting for variations in geometry, sampling densities on both endpoints of the visibility queries, and the light signal itself. Compared to previous approaches for approximating visibility, e.g. shadow mapping, our method has several advantages: (1) it allows caching of arbitrary visibility queries between surface points and is thus applicable to all ray tracing based methods; (2) the approximation error is uniform over the entire image and can be bounded by a user-specified parameter; (3) the cache is created on-the-fly and does not waste any resources on queries that will never be used. We demonstrate the benefits of our method on Whitted-style ray tracing combined with instant radiosity, as well as an integration with bidirectional path tracing.
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    Path Space Regularization for Holistic and Robust Light Transport
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Kaplanyan, Anton S.; Dachsbacher, Carsten; I. Navazo, P. Poulin
    We propose a simple yet powerful regularization framework for robust light transport simulation. It builds on top of existing unbiased methods and resorts to a consistent estimation using regularization only for paths which cannot be sampled in an unbiased way. To introduce as little bias as possible, we selectively regularize individual interactions along paths, and also derive the regularization consistency conditions. Our approach is compatible with the majority of unbiased methods, e.g. (bidirectional) path tracing and Metropolis light transport (MLT), and only a simple modification is required to adapt existing renderers. We compare to recent unbiased and consistent methods and show examples of scenes with difficult light paths, where regularization is required to account for all illumination features. When coupled with MLT we are able to sample all phenomena, like recent consistent methods, while achieving superior convergence.