35-Issue 4

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https://diglib.eg.org/handle/10.2312/15440

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Browsing 35-Issue 4 by Subject "Picture/Image Generation"

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    Efficient Ray Tracing Through Aspheric Lenses and Imperfect Bokeh Synthesis
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Joo, Hyuntae; Kwon, Soonhyeon; Lee, Sangmin; Eisemann, Elmar; Lee, Sungkil; Elmar Eisemann and Eugene Fiume
    We present an efficient ray-tracing technique to render bokeh effects produced by parametric aspheric lenses. Contrary to conventional spherical lenses, aspheric lenses do generally not permit a simple closed-form solution of ray-surface intersections. We propose a numerical root-finding approach, which uses tight proxy surfaces to ensure a good initialization and convergence behavior. Additionally, we simulate mechanical imperfections resulting from the lens fabrication via a texture-based approach. Fractional Fourier transform and spectral dispersion add additional realism to the synthesized bokeh effect. Our approach is well-suited for execution on graphics processing units (GPUs) and we demonstrate complex defocus-blur and lens-flare effects.
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    Forward Light Cuts: A Scalable Approach to Real-Time Global Illumination
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Laurent, Gilles; Delalandre, Cyril; Rivière, Grégoire de La; Boubekeur, Tamy; Elmar Eisemann and Eugene Fiume
    We present Forward Light Cuts, a novel approach to real-time global illumination using forward rendering techniques. We focus on unshadowed diffuse interactions for the first indirect light bounce in the context of large models such as the complex scenes usually encountered in CAD application scenarios. Our approach efficiently generates and uses a multiscale radiance cache by exploiting the geometry-specific stages of the graphics pipeline, namely the tessellator unit and the geometry shader. To do so, we assimilate virtual point lights to the scene's triangles and design a stochastic decimation process chained with a partitioning strategy that accounts for both close-by strong light reflections, and distant regions from which numerous virtual point lights collectively contribute strongly to the end pixel. Our probabilistic solution is supported by a mathematical analysis and a number of experiments covering a wide range of application scenarios. As a result, our algorithm requires no precomputation of any kind, is compatible with dynamic view points, lighting condition, geometry and materials, and scales to tens of millions of polygons on current graphics hardware.
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    Perceptually Motivated BRDF Comparison using Single Image
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Havran, Vlastimil; Filip, Jiri; Myszkowski, Karol; Elmar Eisemann and Eugene Fiume
    Surface reflectance of real-world materials is now widely represented by the bidirectional reflectance distribution function (BRDF) and also by spatially varying representations such as SVBRDF and the bidirectional texture function (BTF). The raw surface reflectance measurements are typically compressed or fitted by analytical models, that always introduce a certain loss of accuracy. For its evaluation we need a distance function between a reference surface reflectance and its approximate version. Although some of the past techniques tried to reflect the perceptual sensitivity of human vision, they have neither optimized illumination and viewing conditions nor surface shape. In this paper, we suggest a new image-based methodology for comparing different anisotropic BRDFs. We use optimization techniques to generate a novel surface which has extensive coverage of incoming and outgoing light directions, while preserving its features and frequencies that are important for material appearance judgments. A single rendered image of such a surface along with simultaneously optimized lighting and viewing directions leads to the computation of a meaningful BRDF difference, by means of standard image difference predictors. A psychophysical experiments revealed that our surface provides richer information on material properties than the standard surfaces often used in computer graphics, e.g., sphere or blob.
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    A Phenomenological Model for Throughfall Rendering in Real-time
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Weber, Yoann; Jolivet, Vincent; Gilet, Guillaume; Nanko, Kazuki; Ghazanfarpour, Djamchid; Elmar Eisemann and Eugene Fiume
    This paper aims at rendering interactive visual effects inherent to complex interactions between trees and rain in real-time in order to increase the realism of natural rainy scenes. Such a complex phenomenon involves a great number of physical processes influenced by various interlinked factors and its rendering represents a thorough challenge in Computer Graphics.We approach this problem by introducing an original method to render drops dripping from leaves after interception of raindrops by foliage. Our method introduces a new hydrological model representing interactions between rain and foliage through a phenomenological approach. Our model reduces the complexity of the phenomenon by representing multiple dripping drops with a new fully functional form evaluated per-pixel on-the-fly and providing improved control over density and physical properties. Furthermore, an efficient real-time rendering scheme, taking full advantage of latest GPU hardware capabilities, allows the rendering of a large number of dripping drops even for complex scenes.
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    Product Importance Sampling for Light Transport Path Guiding
    (The Eurographics Association and John Wiley & Sons Ltd., 2016) Herholz, Sebastian; Elek, Oskar; Vorba, Jiří; Lensch, Hendrik; Křivánek, Jaroslav; Elmar Eisemann and Eugene Fiume
    The efficiency of Monte Carlo algorithms for light transport simulation is directly related to their ability to importance-sample the product of the illumination and reflectance in the rendering equation. Since the optimal sampling strategy would require knowledge about the transport solution itself, importance sampling most often follows only one of the known factors - BRDF or an approximation of the incident illumination. To address this issue, we propose to represent the illumination and the reflectance factors by the Gaussian mixture model (GMM), which we fit by using a combination of weighted expectation maximization and non-linear optimization methods. The GMM representation then allows us to obtain the resulting product distribution for importance sampling on-the-fly at each scene point. For its efficient evaluation and sampling we preform an up-front adaptive decimation of both factor mixtures. In comparison to state-of-the-art sampling methods, we show that our product importance sampling can lead to significantly better convergence in scenes with complex illumination and reflectance.