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Item Global Illumination Shadow Layers(The Eurographics Association and John Wiley & Sons Ltd., 2019) DESRICHARD, François; Vanderhaeghe, David; PAULIN, Mathias; Boubekeur, Tamy and Sen, PradeepComputer graphics artists often resort to compositing to rework light effects in a synthetic image without requiring a new render. Shadows are primary subjects of artistic manipulation as they carry important stylistic information while our perception is tolerant with their editing. In this paper we formalize the notion of global shadow, generalizing direct shadow found in previous work to a global illumination context. We define an object's shadow layer as the difference between two altered renders of the scene. A shadow layer contains the radiance lost on the camera film because of a given object. We translate this definition in the theoretical framework of Monte-Carlo integration, obtaining a concise expression of the shadow layer. Building on it, we propose a path tracing algorithm that renders both the original image and any number of shadow layers in a single pass: the user may choose to separate shadows on a per-object and per-light basis, enabling intuitive and decoupled edits.Item Real-time Image-based Lighting of Microfacet BRDFs with Varying Iridescence(The Eurographics Association and John Wiley & Sons Ltd., 2019) Kneiphof, Tom; Golla, Tim; Klein, Reinhard; Boubekeur, Tamy and Sen, PradeepIridescence is a natural phenomenon that is perceived as gradual color changes, depending on the view and illumination direction. Prominent examples are the colors seen in oil films and soap bubbles. Unfortunately, iridescent effects are particularly difficult to recreate in real-time computer graphics. We present a high-quality real-time method for rendering iridescent effects under image-based lighting. Previous methods model dielectric thin-films of varying thickness on top of an arbitrary micro-facet model with a conducting or dielectric base material, and evaluate the resulting reflectance term, responsible for the iridescent effects, only for a single direction when using real-time image-based lighting. This leads to bright halos at grazing angles and over-saturated colors on rough surfaces, which causes an unnatural appearance that is not observed in ground truth data. We address this problem by taking the distribution of light directions, given by the environment map and surface roughness, into account when evaluating the reflectance term. In particular, our approach prefilters the first and second moments of the light direction, which are used to evaluate a filtered version of the reflectance term. We show that the visual quality of our approach is superior to the ones previously achieved, while having only a small negative impact on performance.Item Tessellated Shading Streaming(The Eurographics Association and John Wiley & Sons Ltd., 2019) Hladky, Jozef; Seidel, Hans-Peter; Steinberger, Markus; Boubekeur, Tamy and Sen, PradeepPresenting high-fidelity 3D content on compact portable devices with low computational power is challenging. Smartphones, tablets and head-mounted displays (HMDs) suffer from thermal and battery-life constraints and thus cannot match the render quality of desktop PCs and laptops. Streaming rendering enables to show high-quality content but can suffer from potentially high latency. We propose an approach to efficiently capture shading samples in object space and packing them into a texture. Streaming this texture to the client, we support temporal frame up-sampling with high fidelity, low latency and high mobility. We introduce two novel sample distribution strategies and a novel triangle representation in the shading atlas space. Since such a system requires dynamic parallelism, we propose an implementation exploiting the power of hardware-accelerated tessellation stages. Our approach allows fast de-coding and rendering of extrapolated views on a client device by using hardwareaccelerated interpolation between shading samples and a set of potentially visible geometry. A comparison to existing shading methods shows that our sample distributions allow better client shading quality than previous atlas streaming approaches and outperforms image-based methods in all relevant aspects.Item Distributing Monte Carlo Errors as a Blue Noise in Screen Space by Permuting Pixel Seeds Between Frames(The Eurographics Association and John Wiley & Sons Ltd., 2019) Heitz, Eric; Belcour, Laurent; Boubekeur, Tamy and Sen, PradeepRecent work has shown that distributing Monte Carlo errors as a blue noise in screen space improves the perceptual quality of rendered images. However, obtaining such distributions remains an open problem with high sample counts and highdimensional rendering integrals. In this paper, we introduce a temporal algorithm that aims at overcoming these limitations. Our algorithm is applicable whenever multiple frames are rendered, typically for animated sequences or interactive applications. Our algorithm locally permutes the pixel sequences (represented by their seeds) to improve the error distribution across frames. Our approach works regardless of the sample count or the dimensionality and significantly improves the images in low-varying screen-space regions under coherent motion. Furthermore, it adds negligible overhead compared to the rendering times.Item Glint Rendering based on a Multiple-Scattering Patch BRDF(The Eurographics Association and John Wiley & Sons Ltd., 2019) Chermain, Xavier; Claux, Frédéric; Mérillou, Stéphane; Boubekeur, Tamy and Sen, PradeepRendering materials such as metallic paints, scratched metals and rough plastics requires glint integrators that can capture all micro-specular highlights falling into a pixel footprint, faithfully replicating surface appearance. Specular normal maps can be used to represent a wide range of arbitrary micro-structures. The use of normal maps comes with important drawbacks though: the appearance is dark overall due to back-facing normals and importance sampling is suboptimal, especially when the micro-surface is very rough. We propose a new glint integrator relying on a multiple-scattering patch-based BRDF addressing these issues. To do so, our method uses a modified version of microfacet-based normal mapping [SHHD17] designed for glint rendering, leveraging symmetric microfacets. To model multiple-scattering, we re-introduce the lost energy caused by a perfectly specular, single-scattering formulation instead of using expensive random walks. This reflectance model is the basis of our patch-based BRDF, enabling robust sampling and artifact-free rendering with a natural appearance. Additional calculation costs amount to about 40% in the worst cases compared to previous methods [YHMR16,CCM18].