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Now showing 1 - 10 of 17
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    Freeform Shadow Boundary Editing
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Mattausch, Oliver; Igarashi, Takeo; Wimmer, Michael; I. Navazo, P. Poulin
    We present an algorithm for artistically modifying physically based shadows. With our tool, an artist can directly edit the shadow boundaries in the scene in an intuitive fashion similar to freeform curve editing. Our algorithm then makes these shadow edits consistent with respect to varying light directions and scene configurations, by creating a shadow mesh from the new silhouettes. The shadow mesh helps a modified shadow volume algorithm cast shadows that conform to the artistic shadow boundary edits, while providing plausible interaction with dynamic environments, including animation of both characters and light sources. Our algorithm provides significantly more fine-grained local and direct control than previous artistic light editing methods, which makes it simple to adjust the shadows in a scene to reach a particular effect, or to create interesting shadow shapes and shadow animations. All cases are handled with a single intuitive interface, be it soft shadows, or (self-)shadows on arbitrary receivers.
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    Latency Considerations of Depth-first GPU Ray Tracing
    (The Eurographics Association, 2014) Guthe, Michael; Eric Galin and Michael Wand
    Despite the potential divergence of depth-first ray tracing [AL09], it is nevertheless the most efficient approach on massively parallel graphics processors. Due to the use of specialized caching strategies that were originally developed for texture access, it has been shown to be compute rather than bandwidth limited. Especially with recents developments however, not only the raw bandwidth, but also the latency for both memory access and read after write register dependencies can become a limiting factor. In this paper we will analyze the memory and instruction dependency latencies of depth first ray tracing. We will show that ray tracing is in fact latency limited on current GPUs and propose three simple strategies to better hide the latencies. This way, we come significantly closer to the maximum performance of the GPU.
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    Volume Ray Casting quality estimation in terms of Peak Signal-to-Noise Ratio
    (The Eurographics Association, 2013) Gavrilov, Nikolay; Turlapov, V.; Miguel Chover and A. Augusto de Sousa
    In spite of a large number of techniques aimed for improvement of Direct Volume Rendering (DVR) quality and performance proposed in the literature, there is a lack of approaches for numerical quality estimation of the images obtained by visualization of medical and scientific volumetric datasets. In this paper we propose a method to estimate sampling artefacts. Using the proposed estimation method we compare different RC algorithms to expose optimal ones in quality-performance criteria.
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    Computing and Fabricating Multiplanar Models
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Chen, Desai; Sitthi-amorn, Pitchaya; Lan, Justin T.; Matusik, Wojciech; I. Navazo, P. Poulin
    We present a method for converting computer 3D models into physical equivalents. More specifically, we address the problem of approximating a 3D textured mesh using a small number of planar polygonal primitives that form a closed surface. This simplified representation allows us to easily manufacture individual components using computer controlled cutters (e.g., laser cutters or CNC machines). These polygonal pieces can be assembled into the final 3D model using internal planar connectors that are manufactured simultaneously. Our shape approximation algorithm iteratively assigns mesh faces to planar segments and slowly deforms these faces towards corresponding segments. This approach ensures that the output for a given closed mesh is still a closed mesh and avoids introducing self-intersections. After this step we also compute the shape of polygonal connectors that internally hold the whole mesh surface. Both the polygonal surface elements and connectors can be manufactured in a single cutting pass. We validate the use of our method by computing and manufacturing a variety of textured polyhedral models.
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    A Tone Reproduction Operator for All Luminance Ranges Considering Human Color Perception
    (The Eurographics Association, 2014) Mikamo, Michihiro; Raytchev, Bisser; Tamaki, Toru; Kaneda, Kazufumi; Eric Galin and Michael Wand
    In this paper, we present a novel tone reproduction operator that is able to handle the color shift that occurs in photopic, mesopic, and scotopic vision, using a model based on a two-stage model of human color vision and psychophysical data obtained from measurements of human color perception. Since conventional methods are limited to generating images under a certain visual condition, it is difficult to apply just one operator to deal with scenes with continuous change within a wide luminance range, such as various scenes in movies. To overcome this problem, we have developed a model based on psychophysical data involving wavelength discrimination within a wide luminance range, which provides us with clues about the change of color perception. That is, the spectral sensitivity shifts toward the short wavelengths and decreases according to the adaptation light levels. By integrating the wavelength discrimination into our model, the proposed operator enables us to compute the transition of color perception under a wide range of viewing conditions.
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    Analytic Visibility on the GPU
    (The Eurographics Association and Blackwell Publishing Ltd., 2013) Auzinger, Thomas; Wimmer, Michael; Jeschke, Stefan; I. Navazo, P. Poulin
    This paper presents a parallel, implementation-friendly analytic visibility method for triangular meshes. Together with an analytic filter convolution, it allows for a fully analytic solution to anti-aliased 3D mesh rendering on parallel hardware. Building on recent works in computational geometry, we present a new edge-triangle intersection algorithm and a novel method to complete the boundaries of all visible triangle regions after a hidden line elimination step. All stages of the method are embarrassingly parallel and easily implementable on parallel hardware. A GPU implementation is discussed and performance characteristics of the method are shown and compared to traditional sampling-based rendering methods.
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    Size-Based Rendering for Lung Cancer Screening
    (The Eurographics Association, 2013) Wiemker, Rafael; BĂĽlow, Thomas; Klinder, Tobias; M.- A. Otaduy and O. Sorkine
    We present two relevant clinical use cases for thoracic computed tomography data, where the recently introduced concept of size-based rendering can be beneficially applied to medical visualization in the context of screening for lung cancer and chronic obstructive pulmonary disease (COPD): (a) Gradual suppression of thorax and vessels for quick appraisal of the presence of pulmonary nodules. (b) Visualization of bullous versus diffuse emphysema. In the first use case, the opacity is chosen to decrease with local structure size, whereas in the second case, the opacity is chosen to increase with structure size. Both algorithms are robust in particular because they do not depend on any prior segmentation or classification. They are ideally suited for full parallelization and GPU implementation.
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    State of the Art of Parallel Coordinates
    (The Eurographics Association, 2013) Heinrich, Julian; Weiskopf, Daniel; M. Sbert and L. Szirmay-Kalos
    This work presents a survey of the current state of the art of visualization techniques for parallel coordinates. It covers geometric models for constructing parallel coordinates and reviews methods for creating and understanding visual representations of parallel coordinates. The classification of these methods is based on a taxonomy that was established from the literature and is aimed at guiding researchers to find existing techniques and identifying white spots that require further research. The techniques covered in this survey are further related to an established taxonomy of knowledge-discovery tasks to support users of parallel coordinates in choosing a technique for their problem at hand. Finally, we discuss the challenges in constructing and understanding parallel-coordinates plots and provide some examples from different application domains.
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    Poisson Image Analogy: Texture-Aware Seamless Cloning
    (The Eurographics Association, 2013) Yoshizawa, Shin; Yokota, Hideo; Miguel Chover and A. Augusto de Sousa
    Synthesizing two images with seamless boundaries, i.e. seamless image cloning, is important and has many useful applications in CG. Previous approaches do not produce realistic results if texture details of the two images are different.We propose a novel texture-aware seamless cloning framework based on separately processing the details and base image colors. The proposed framework provides realistic cloning results with seamless texture details.
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    Towards a Physically Plausible Constrained Shader Graph System for Predictive Rendering
    (The Eurographics Association, 2013) PavlĂ­k, Ivo; Wilkie, Alexander; Miguel Chover and A. Augusto de Sousa
    We present ongoing work on a modeling tool for Predictive Rendering based on the popular idea of shader graphs for description of object surfaces. To guarantee physical plausibility of the resulting materials, we use a restricted approach that only allows us to build the shader graphs by using physically safe surface models and physically safe manipulation operators. The tool also allows us to manipulate material properties - fluorescence and polarisation - which can affect object appearance, but are usually missing in other modeling toolsets. Since there is a rising demand for realism of the modelled material appearance among CG content creators, the concept of a restricted shader graph is also useful in the context of common photorealistic renderers.