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Now showing 1 - 10 of 16
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    Quad-Based Fourier Transform for Efficient Diffraction Synthesis
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Scandolo, Leonardo; Lee, Sungkil; Eisemann, Elmar; Jakob, Wenzel and Hachisuka, Toshiya
    Far-field diffraction can be evaluated using the Discrete Fourier Transform (DFT) in image space but it is costly due to its dense sampling. We propose a technique based on a closed-form solution of the continuous Fourier transform for simple vector primitives (quads) and propose a hierarchical and progressive evaluation to achieve real-time performance. Our method is able to simulate diffraction effects in optical systems and can handle varying visibility due to dynamic light sources. Furthermore, it seamlessly extends to near-field diffraction. We show the benefit of our solution in various applications, including realistic real-time glare and bloom rendering.
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    Stratified Sampling of Projected Spherical Caps
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Ureña, Carlos; Georgiev, Iliyan; Jakob, Wenzel and Hachisuka, Toshiya
    We present a method for uniformly sampling points inside the projection of a spherical cap onto a plane through the sphere's center. To achieve this, we devise two novel area-preserving mappings from the unit square to this projection, which is often an ellipse but generally has a more complex shape. Our maps allow for low-variance rendering of direct illumination from finite and infinite (e.g. sun-like) spherical light sources by sampling their projected solid angle in a stratified manner. We discuss the practical implementation of our maps and show significant quality improvement over traditional uniform spherical cap sampling in a production renderer.
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    Spectral Gradient Sampling for Path Tracing
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Petitjean, Victor; Bauszat, Pablo; Eisemann, Elmar; Jakob, Wenzel and Hachisuka, Toshiya
    Spectral Monte-Carlo methods are currently the most powerful techniques for simulating light transport with wavelengthdependent phenomena (e.g., dispersion, colored particle scattering, or diffraction gratings). Compared to trichromatic rendering, sampling the spectral domain requires significantly more samples for noise-free images. Inspired by gradient-domain rendering, which estimates image gradients, we propose spectral gradient sampling to estimate the gradients of the spectral distribution inside a pixel. These gradients can be sampled with a significantly lower variance by carefully correlating the path samples of a pixel in the spectral domain, and we introduce a mapping function that shifts paths with wavelength-dependent interactions. We compute the result of each pixel by integrating the estimated gradients over the spectral domain using a onedimensional screened Poisson reconstruction. Our method improves convergence and reduces chromatic noise from spectral sampling, as demonstrated by our implementation within a conventional path tracer.
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    Progressive Multi-Jittered Sample Sequences
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Christensen, Per; Kensler, Andrew; Kilpatrick, Charlie; Jakob, Wenzel and Hachisuka, Toshiya
    We introduce three new families of stochastic algorithms to generate progressive 2D sample point sequences. This opens a general framework that researchers and practitioners may find useful when developing future sample sequences. Our best sequences have the same low sampling error as the best known sequence (a particular randomization of the Sobol' (0,2) sequence). The sample points are generated using a simple, diagonally alternating strategy that progressively fills in holes in increasingly fine stratifications. The sequences are progressive (hierarchical): any prefix is well distributed, making them suitable for incremental rendering and adaptive sampling. The first sample family is only jittered in 2D; we call it progressive jittered. It is nearly identical to existing sample sequences. The second family is multi-jittered: the samples are stratified in both 1D and 2D; we call it progressive multi-jittered. The third family is stratified in all elementary intervals in base 2, hence we call it progressive multi-jittered (0,2). We compare sampling error and convergence of our sequences with uniform random, best candidates, randomized quasi-random sequences (Halton and Sobol'), Ahmed's ART sequences, and Perrier's LDBN sequences. We test the sequences on function integration and in two settings that are typical for computer graphics: pixel sampling and area light sampling. Within this new framework we present variations that generate visually pleasing samples with blue noise spectra, and well-stratified interleaved multi-class samples; we also suggest possible future variations.
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    Runtime Shader Simplification via Instant Search in Reduced Optimization Space
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Yuan, Yazhen; Wang, Rui; Hu, Tianlei; Bao, Hujun; Jakob, Wenzel and Hachisuka, Toshiya
    Traditional automatic shader simplification simplifies shaders in an offline process, which is typically carried out in a contextoblivious manner or with the use of some example contexts, e.g., certain hardware platforms, scenes, and uniform parameters, etc. As a result, these pre-simplified shaders may fail at adapting to runtime changes of the rendering context that were not considered in the simplification process. In this paper, we propose a new automatic shader simplification technique, which explores two key aspects of a runtime simplification framework: the optimization space and the instant search for optimal simplified shaders with runtime context. The proposed technique still requires a preprocess stage to process the original shader. However, instead of directly computing optimal simplified shaders, the proposed preprocess generates a reduced shader optimization space. In particular, two heuristic estimates of the quality and performance of simplified shaders are presented to group similar variants into representative ones, which serve as basic graph nodes of the simplification dependency graph (SDG), a new representation of the optimization space. At the runtime simplification stage, a parallel discrete optimization algorithm is employed to instantly search in the SDG for optimal simplified shaders. New data-driven cost models are proposed to predict the runtime quality and performance of simplified shaders on the basis of data collected during runtime. Results show that the selected simplifications of complex shaders achieve 1.6 to 2.5 times speedup and still retain high rendering quality.
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    Deep Painting Harmonization
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Luan, Fujun; Paris, Sylvain; Shechtman, Eli; Bala, Kavita; Jakob, Wenzel and Hachisuka, Toshiya
    Copying an element from a photo and pasting it into a painting is a challenging task. Applying photo compositing techniques in this context yields subpar results that look like a collage - and existing painterly stylization algorithms, which are global, perform poorly when applied locally. We address these issues with a dedicated algorithm that carefully determines the local statistics to be transferred. We ensure both spatial and inter-scale statistical consistency and demonstrate that both aspects are key to generating quality results. To cope with the diversity of abstraction levels and types of paintings, we introduce a technique to adjust the parameters of the transfer depending on the painting. We show that our algorithm produces significantly better results than photo compositing or global stylization techniques and that it enables creative painterly edits that would be otherwise difficult to achieve.
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    Acquisition and Validation of Spectral Ground Truth Data for Predictive Rendering of Rough Surfaces
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Clausen, Olaf; Marroquim, Ricardo; Fuhrmann, Arnulph; Jakob, Wenzel and Hachisuka, Toshiya
    Physically based rendering uses principles of physics to model the interaction of light with matter. Even though it is possible to achieve photorealistic renderings, it often fails to be predictive. There are two major issues: first, there is no analytic material model that considers all appearance critical characteristics; second, light is in many cases described by only 3 RGB-samples. This leads to the problem that there are different models for different material types and that wavelength dependent phenomena are only approximated. In order to be able to analyze the influence of both problems on the appearance of real world materials, an accurate comparison between rendering and reality is necessary. Therefore, in this work, we acquired a set of precisely and spectrally resolved ground truth data. It consists of the precise description of a new developed reference scene including isotropic BRDFs of 24 color patches, as well as the reference measurements of all patches under 13 different angles inside the reference scene. Our reference data covers rough materials with many different spectral distributions and various illumination situations, from direct light to indirect light dominated situations.
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    Thin Structures in Image Based Rendering
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Thonat, Theo; Djelouah, Abdelaziz; Durand, Fredo; Drettakis, George; Jakob, Wenzel and Hachisuka, Toshiya
    We propose a novel method to handle thin structures in Image-Based Rendering (IBR), and specifically structures supported by simple geometric shapes such as planes, cylinders, etc. These structures, e.g. railings, fences, oven grills etc, are present in many man-made environments and are extremely challenging for multi-view 3D reconstruction, representing a major limitation of existing IBR methods. Our key insight is to exploit multi-view information. After a handful of user clicks to specify the supporting geometry, we compute multi-view and multi-layer alpha mattes to extract the thin structures. We use two multi-view terms in a graph-cut segmentation, the first based on multi-view foreground color prediction and the second ensuring multiview consistency of labels. Occlusion of the background can challenge reprojection error calculation and we use multiview median images and variance, with multiple layers of thin structures. Our end-to-end solution uses the multi-layer segmentation to create per-view mattes and the median colors and variance to create a clean background. We introduce a new multi-pass IBR algorithm based on depth-peeling to allow free-viewpoint navigation of multi-layer semi-transparent thin structures. Our results show significant improvement in rendering quality for thin structures compared to previous image-based rendering solutions.
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    Eurographics Symposium on Rendering: Frontmatter
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Jakob, Wenzel; Hachisuka, Toshiya; Jakob, Wenzel and Hachisuka, Toshiya
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    Exploiting Repetitions for Image-Based Rendering of Facades
    (The Eurographics Association and John Wiley & Sons Ltd., 2018) Rodriguez, Simon; Bousseau, Adrien; Durand, Fredo; Drettakis, George; Jakob, Wenzel and Hachisuka, Toshiya
    Street-level imagery is now abundant but does not have sufficient capture density to be usable for Image-Based Rendering (IBR) of facades. We present a method that exploits repetitive elements in facades - such as windows - to perform data augmentation, in turn improving camera calibration, reconstructed geometry and overall rendering quality for IBR. The main intuition behind our approach is that a few views of several instances of an element provide similar information to many views of a single instance of that element. We first select similar instances of an element from 3-4 views of a facade and transform them into a common coordinate system, creating a ''platonic'' element. We use this common space to refine the camera calibration of each view of each instance and to reconstruct a 3D mesh of the element with multi-view stereo, that we regularize to obtain a piecewise-planar mesh aligned with dominant image contours. Observing the same element under multiple views also allows us to identify reflective areas - such as glass panels - which we use at rendering time to generate plausible reflections using an environment map. Our detailed 3D mesh, augmented set of views, and reflection mask enable image-based rendering of much higher quality than results obtained using the input images directly.