Browsing by Author "Peters, Christoph"

Now showing 1 - 8 of 8
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    BRDF Importance Sampling for Linear Lights
    (The Eurographics Association and John Wiley & Sons Ltd., 2021) Peters, Christoph; Binder, Nikolaus and Ritschel, Tobias
    We introduce an efficient method to sample linear lights, i.e. infinitesimally thin cylinders, proportional to projected solid angle. Our method uses inverse function sampling with a specialized iterative procedure that converges to high accuracy in only two iterations. It also allows us to sample proportional to a linearly transformed cosine. By combining both sampling techniques through suitable multiple importance sampling heuristics and by using good stratification, we achieve unbiased diffuse and specular real-time shading with low variance outside penumbrae at two samples per pixel. Additionally, we provide a fast method for solid angle sampling.
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    Moment-Based Methods for Real-Time Shadows and Fast Transient Imaging
    (Universitäts- und Landesbibliothek Bonn, 2017-12-06) Peters, Christoph
    We apply the theory of moments to develop computationally efficient methods for real-time rendering of shadows and reconstruction of transient images from few measurements. Given moments of an unknown probability distribution, i.e. the expectations of known, real random variables, the theory of moments strives to characterize all distributions that could have led to these moments. Earlier works in computer graphics only use the most basic results of this powerful theory. When filtering shadows based on shadow maps, the distribution of depth values within the filter region has to be estimated. Variance shadow mapping does this using two power moments. While this linear representation admits direct filtering, it leads to a very coarse reconstruction. We generalize this approach to use an arbitrary set of general moments and benchmark thousands of possible choices. Based on the results, we propose the use of moment shadow mapping which produces high-quality antialiased shadows efficiently by storing four power moments in 64 bits per shadow map texel. Techniques for shadow map filtering have been applied to a variety of problems. We combine these existing approaches with moment shadow mapping to render shadows of translucent occluders using alpha blending, soft shadows using summed-area tables and prefiltered single scattering using six power moments. All these techniques have a high overhead per texel of the moment shadow map but a low overhead per shaded pixel. Thus, they scale well to the increasingly high resolutions of modern displays. Transient images help to analyze light transport in scenes. Besides two spatial dimensions, they are resolved in time of flight. Earlier cost-efficient approaches reconstruct them from measurements of amplitude modulated continuous wave lidar systems but they typically take more than a minute of capture time. We pose this reconstruction problem as trigonometric moment problem. The maximum entropy spectral estimate and the Pisarenko estimate are known closed-form solutions to such problems which yield continuous and sparse reconstructions, respectively. By applying them, we reconstruct complex impulse responses with m distinct returns from measurements at as few as m non-zero frequencies. For m=3 our experiments with measured data confirm this. Thus, our techniques are computationally efficient and simultaneously reduce capture times drastically. We successfully capture 18.6 transient images per second which leads to transient video. As an important byproduct, this fast and accurate reconstruction of impulse responses enables removal of multipath interference in range images.
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    Moment-Based Opacity Optimization
    (The Eurographics Association, 2020) Zeidan, Mahmoud; Rapp, Tobias; Peters, Christoph; Dachsbacher, Carsten; Frey, Steffen and Huang, Jian and Sadlo, Filip
    Geometric structures such as points, lines, and surfaces play a vital role in scientific visualization. However, these visualizations frequently suffer from visual clutter that hinders the inspection of important features behind dense but less important features. In the past few years, geometric cluttering and occlusion avoidance has been addressed in scientific visualization with various approaches such as opacity optimization techniques. In this paper, we present a novel approach for opacity optimization based on recent state-of-the-art moment-based techniques for signal reconstruction. In contrast to truncated Fourier series, momentbased reconstructions of feature importance and optical depth along view rays are highly accurate for sparse regions but also plausible for densely covered regions. At the same time, moment-based methods do not suffer from ringing artifacts. Moreover, this representation enables fast evaluation and compact storage, which is crucial for per-pixel optimization especially for large geometric structures. We also present a fast screen space filtering approach for optimized opacities that works directly on moment buffers. This filtering approach is suitable for real-time visualization applications, while providing comparable quality to object space smoothing. Its implementation is independent of the type of geometry such that it is general and easy to integrate. We compare our technique to recent state of the art techniques for opacity optimization and apply it to real and synthetic data sets in various applications.
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    Ray Tracing Spherical Harmonics Glyphs
    (The Eurographics Association, 2023) Peters, Christoph; Patel, Tark; Usher, Will; Johnson, Chris R.; Guthe, Michael; Grosch, Thorsten
    Spherical harmonics glyphs are an established way to visualize high angular resolution diffusion imaging data. Starting from a unit sphere, each point on the surface is scaled according to the value of a linear combination of spherical harmonics basis functions. The resulting glyph visualizes an orientation distribution function. We present an efficient method to render these glyphs using ray tracing. Our method constructs a polynomial whose roots correspond to ray-glyph intersections. This polynomial has degree 2k+2 for spherical harmonics bands 0;2; : : : ; k. We then find all intersections in an efficient and numerically stable fashion through polynomial root finding. Our formulation also gives rise to a simple formula for normal vectors of the glyph. Additionally, we compute a nearly exact axis-aligned bounding box to make ray tracing of these glyphs even more efficient. Since our method finds all intersections for arbitrary rays, it lets us perform sophisticated shading and uncertainty visualization. Compared to prior work, it is faster, more flexible and more accurate.
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    Real-Time Ray Tracing of Micro-Poly Geometry with Hierarchical Level of Detail
    (The Eurographics Association and John Wiley & Sons Ltd., 2023) Benthin, Carsten; Peters, Christoph; Bikker, Jacco; Gribble, Christiaan
    In recent work, Nanite has demonstrated how to rasterize virtualized micro-poly geometry in real time, thus enabling immense geometric complexity. We present a system that employs similar methods for real-time ray tracing of micro-poly geometry. The geometry is preprocessed in almost the same fashion: Nearby triangles are clustered together and clusters get merged and simplified to obtain hierarchical level of detail (LOD). Then these clusters are compressed and stored in a GPU-friendly data structure. At run time, Nanite selects relevant clusters, decompresses them and immediately rasterizes them. Instead of rasterization, we decompress each selected cluster into a small bounding volume hierarchy (BVH) in the format expected by the ray tracing hardware. Then we build a complete BVH on top of the bounding volumes of these clusters and use it for ray tracing. Our BVH build reaches more than 74% of the attainable peak memory bandwidth and thus it can be done per frame. Since LOD selection happens per frame at the granularity of clusters, all triangles cover a small area in screen space.
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    Spectral Rendering with the Bounded MESE and sRGB Data
    (The Eurographics Association, 2019) Peters, Christoph; Merzbach, Sebastian; Hanika, Johannes; Dachsbacher, Carsten; Klein, Reinhard and Rushmeier, Holly
    In a recent journal paper, we introduced a technique to represent reflectance spectra by an arbitrary number of Fourier coefficients. As a special case, we converted tristimulus data to three Fourier coefficients. After summarizing this work, we introduce the Fourier sRGB color space. It is defined in terms of Fourier coefficients but designed to behave similar to sRGB. Textures stored in Fourier sRGB support efficient spectral rendering but can be compressed with techniques designed for sRGB textures. Compression errors are similar to sRGB.
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    Temporally Stable Real-Time Joint Neural Denoising and Supersampling
    (ACM Association for Computing Machinery, 2022) Thomas, Manu Mathew; Liktor, Gabor; Peters, Christoph; Kim, Sungye; Vaidyanathan, Karthik; Forbes, Angus G.; Josef Spjut; Marc Stamminger; Victor Zordan
    Recent advances in ray tracing hardware bring real-time path tracing into reach, and ray traced soft shadows, glossy reflections, and diffuse global illumination are now common features in games. Nonetheless, ray budgets are still limited. This results in undersampling, which manifests as aliasing and noise. Prior work addresses these issues separately. While temporal supersampling methods based on neural networks have gained a wide use in modern games due to their better robustness, neural denoising remains challenging because of its higher computational cost. We introduce a novel neural network architecture for real-time rendering that combines supersampling and denoising, thus lowering the cost compared to two separate networks. This is achieved by sharing a single low-precision feature extractor with multiple higher-precision filter stages. To reduce cost further, our network takes low-resolution inputs and reconstructs a high-resolution denoised supersampled output. Our technique produces temporally stable high-fidelity results that significantly outperform state-of-the-art real-time statistical or analytical denoisers combined with TAA or neural upsampling to the target resolution. We introduce a novel neural network architecture for real-time rendering that combines supersampling and denoising, thus lowering the cost compared to two separate networks. This is achieved by sharing a single low-precision feature extractor with multiple higher-precision filter stages. To reduce cost further, our network takes low-resolution inputs and reconstructs a high-resolution denoised supersampled output. Our technique produces temporally stable high-fidelity results that significantly outperform state-of-the-art real-time statistical or analytical denoisers combined with TAA or neural upsampling to the target resolution.
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    Versatile Geometric Flow Visualization by Controllable Shape and Volumetric Appearance
    (The Eurographics Association, 2022) Zeidan, Mahmoud; Peters, Christoph; Rapp, Tobias; Dachsbacher, Carsten; Cabiddu, Daniela; Schneider, Teseo; Allegra, Dario; Catalano, Chiara Eva; Cherchi, Gianmarco; Scateni, Riccardo
    We present a novel visualization technique for geometry-based visualization of vector fields. Our approach generalizes and combines several existing approaches in a flexible framework using a scalable GPU-accelerated implementation. We map characteristic lines to a variety of glyphs. The user can define multiple cross-sectional shapes that will be used for extrusion. Our system interpolates between these shapes as requested, either based on attributes of the vector field and the characteristic lines or using global user-controlled parameters. Thus, a single characteristic line can use different cross-sectional shapes in different parts to aid the visualization of different phenomena. Transitions can be smooth or discrete and we support highlighting of silhouettes. Additionally, we track and visualize the rotation in the vector field and offer full control of the color mapping, the opacity and the radii along the characteristic lines. Texture-based approaches such as 3D line integral convolution (3D LIC) offer another avenue to vector field visualization. In 3D, they typically rely on sparsely placed seed points. We emulate their appearance with our geometry-based approach through an approximation of the volume integral within our glyphs. Combined with fast order-independent transparency, our GPU implementation achieves fast rendering, even at high resolutions, while keeping the memory footprint moderate.