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Item Spherical Barycentric Coordinates(The Eurographics Association, 2006) Langer, Torsten; Belyaev, Alexander; Seidel, Hans-Peter; Alla Sheffer and Konrad PolthierWe develop spherical barycentric coordinates. Analogous to classical, planar barycentric coordinates that describe the positions of points in a plane with respect to the vertices of a given planar polygon, spherical barycentric coordinates describe the positions of points on a sphere with respect to the vertices of a given spherical polygon. In particular, we introduce spherical mean value coordinates that inherit many good properties of their planar counterparts. Furthermore, we present a construction that gives a simple and intuitive geometric interpretation for classical barycentric coordinates, like Wachspress coordinates, mean value coordinates, and discrete harmonic coordinates. One of the most interesting consequences is the possibility to construct mean value coordinates for arbitrary polygonal meshes. So far, this was only possible for triangular meshes. Furthermore, spherical barycentric coordinates can be used for all applications where only planar barycentric coordinates were available up to now. They include Bézier surfaces, parameterization, free-form deformations, and interpolation of rotations.Item Overfitting Control for Surface Reconstruction(The Eurographics Association, 2006) Lee, Yunjin; Lee, Seungyong; Ivrissimtzis, Ioannis; Seidel, Hans-Peter; Alla Sheffer and Konrad PolthierThis paper proposes a general framework for overfitting control in surface reconstruction from noisy point data. The problem we deal with is how to create a model that will capture as much detail as possible and simultaneously avoid reproducing the noise of the input points. The proposed framework is based on extra-sample validation. It is fully automatic and can work in conjunction with any surface reconstruction algorithm. We test the framework with a Radial Basis Function algorithm, Multi-level Partition of Unity implicits, and the Power Crust algorithm.Item Analysis of Reproducing Real-World Appearance on Displays of Varying Dynamic Range(The Eurographics Association and Blackwell Publishing, Inc, 2006) Yoshida, Akiko; Mantiuk, Rafal; Myszkowski, Karol; Seidel, Hans-PeterWe conduct a series of experiments to investigate the desired properties of a tone mapping operator (TMO) and to design such an operator based on subjective data. We propose a novel approach to the tone mapping problem, in which the tone mapping parameters are determined based on the data from subjective experiments, rather than an image processing algorithm or a visual model. To collect this data, a series of experiments are conducted in which the subjects adjust three generic TMO parameters: brightness, contrast and color saturation. In two experiments, the subjects are to find a) the most preferred image without a reference image (preference task) and b) the closest image to the real-world scene which the subjects are confronted with (fidelity task). We analyze subjects choice of parameters to provide more intuitive control over the parameters of a tone mapping operator. Unlike most of the researched TMOs that focus on rendering for standard low dynamic range monitors, we consider a broad range of potential displays, each offering different dynamic range and brightness. We simulate capabilities of such displays on a high dynamic range (HDR) display. This allows us to address the question of how tone mapping needs to be adjusted to accommodate displays with drastically different dynamic ranges.Categories and Subject Descriptors (according to ACM CCS): I.3.8 [Computer Graphics]: High dynamic range images, Visual perception, Tone mappingItem Beyond Tone Mapping: Enhanced Depiction of Tone Mapped HDR Images(The Eurographics Association and Blackwell Publishing, Inc, 2006) Smith, Kaleigh; Krawczyk, Grzegorz; Myszkowski, Karol; Seidel, Hans-PeterHigh Dynamic Range (HDR) images capture the full range of luminance present in real world scenes, and unlike Low Dynamic Range (LDR) images, can simultaneously contain detailed information in the deepest of shadows and the brightest of light sources. For display or aesthetic purposes, it is often necessary to perform tone mapping, which creates LDR depictions of HDR images at the cost of contrast information loss. The purpose of this work is two-fold: to analyze a displayed LDR image against its original HDR counterpart in terms of perceived contrast distortion, and to enhance the LDR depiction with perceptually driven colour adjustments to restore the original HDR contrast information. For analysis, we present a novel algorithm for the characterization of tone mapping distortion in terms of observed loss of global contrast, and loss of contour and texture details. We classify existing tone mapping operators accordingly. We measure both distortions with perceptual metrics that enable the automatic and meaningful enhancement of LDR depictions. For image enhancement, we identify artistic and photographic colour techniques from which we derive adjustments that create contrast with colour. The enhanced LDR image is an improved depiction of the original HDR image with restored contrast information.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.4.0 [Image Processing and Computer Vision]: GeneralImage processing softwareItem Ray Tracing Animated Scenes using Motion Decomposition(The Eurographics Association and Blackwell Publishing, Inc, 2006) Guenther, Johannes; Friedrich, Heiko; Wald, Ingo; Seidel, Hans-Peter; Slusallek, PhilippThough ray tracing has recently become interactive, its high precomputation time for building spatial indices usually limits its applications to walkthroughs of static scenes. This is a major limitation, as most applications demand support for dynamically animated models. In this paper, we present a new approach to ray trace a special but important class of dynamic scenes, namely models whose connectivity does not change over time and for which all possible poses are known in advance.We support these kinds of models by introducing two new concepts: motion decomposition, and fuzzy kd-trees. We analyze the animation and break the model down into submeshes with similar motion. For each of these submeshes and for every time step, we calculate a best affine transformation through a least square approach. Any residual motion is then captured in a single "fuzzy kd-tree" for the entire animation.Together, these techniques allow for ray tracing animations without rebuilding the spatial index structures for the submeshes, resulting in interactive frame rates of 5 to 15 fps even on a single CPU.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Ray tracing I.3.6 [Methodology and Techniques]: Graphics data structures and data typesItem Volumetric Density Capture From a Single Image(The Eurographics Association, 2006) Fuchs, Christian; Chen, Tongbo; Goesele, Michael; Theisel, Holger; Seidel, Hans-Peter; Raghu Machiraju and Torsten MoellerWe propose a new approach to capture the volumetric density of scattering media instantaneously with a single image. The volume is probed with a set of laser lines and the scattered intensity is recorded by a conventional camera. We then determine the density along the laser lines taking the scattering properties of the media into account. A specialized interpolation technique reconstructs the full density field in the volume. We apply the technique to capture the volumetric density of participating media such as smoke.Item Template Deformation for Point Cloud Fitting(The Eurographics Association, 2006) Stoll, Carsten; Karni, Zachi; Rössl, Christian; Yamauchi, Hitoshi; Seidel, Hans-Peter; Mario Botsch and Baoquan Chen and Mark Pauly and Matthias ZwickerThe reconstruction of high-quality surface meshes from measured data is a vital stage in digital shape processing. We present a new approach to this problem that deforms a template surface to fit a given point cloud. Our method takes a template mesh and a point cloud as input, the latter typically shows missing parts and measurement noise. The deformation process is initially guided by user specified correspondences between template and data, then during iterative fitting new correspondences are established. This approach is based on a Laplacian setting for the template without need of any additional meshing of the data or cross-parameterization. The reconstructed surface fits to the point cloud while it inherits shape properties and topology of the template. We demonstrate the effectiveness of the approach for several point data sets from different sources.