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Item Measurement-Based Interactive Simulation of Viscoelastic Solids(The Eurographics Association and Blackwell Publishing, Inc, 2004) Schoner, Jeffrey L.; Lang, Jochen; Seidel, Hans-PeterAnimation of viscoelastic solids in entertainment and medical applications as well as scientific simulation can be improved through observations of real world objects. This paper presents a method for simulating viscoelastic solids in real-time for visual and haptic display along with a method for determining the parameters of the the underlying model from automated physical measurements of real world objects. The viscoelastic model is a novel extension of the discrete Green's function matrix for linear elasticity, which combines static behavior represented by Green's functions with dynamic behavior expressed by differential equations inspired by particle systems. We describe a novel estimation method of dynamic contact behavior for heterogeneous complex objects based on these measurements. For this estimation, our method relies only on measurement data previously used in the acquisition less realistic elastostatic models. In this way our method allows more physically accurate realism in animation of viscoelastic solids without large additional computational costs or any measurements besides those associated with related methods for elastostatic solids.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Physically based modeling I.3.7 [Computer Graphics]: Virtual reality, animationItem Exchanging Faces in Images(The Eurographics Association and Blackwell Publishing, Inc, 2004) Blanz, Volker; Scherbaum, Kristina; Vetter, Thomas; Seidel, Hans-PeterPasting somebody's face into an existing image with traditional photo retouching and digital image processing tools has only been possible if both images show the face from the same viewpoint and with the same illumination. However, this is rarely the case for given pairs of images. We present a system that exchanges faces across large differences in viewpoint and illumination. It is based on an algorithm that estimates 3D shape and texture along with all relevant scene parameters, such as pose and lighting, from single images. Manual interaction is reduced to clicking on a set of about 7 feature points, and marking the hairline in the target image. The system can be used for image processing, virtual try-on of hairstyles, and face recognition. By separating face identity from imaging conditions, our approach provides an abstract representation of images and a novel, high-level tool for image manipulation.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: AnimationItem Spline Approximation of General Volumetric Data(The Eurographics Association, 2004) Roessl, C.; Zeilfelder, F.; Nuernberger, G.; Seidel, Hans-Peter; Gershon Elber and Nicholas Patrikalakis and Pere BrunetWe present an efficient algorithm for approximating huge general volumetric data sets, i.e. the data is given over arbitrarily shaped volumes and consists of up to millions of samples. The method is based on cubic trivariate splines, i.e. piecewise polynomials of total degree three defined w.r.t. uniform type-6 tetrahedral partitions of the volumetric domain. Similar as in the recent bivariate approximation approaches (cf. [10, 15]), the splines in three variables are automatically determined from the discrete data as a result of a two-step method (see [40]), where local discrete least squares polynomial approximations of varying degrees are extended by using natural conditions, i.e. the continuity and smoothness properties which determine the underlying spline space. The main advantages of this approach with linear algorithmic complexity are as follows: no tetrahedral partition of the volume data is needed, only small linear systems have to be solved, the local variation and distribution of the data is automatically adapted, Bernstein-Bézier techniques well-known in Computer Aided Geometric Design (CAGD) can be fully exploited, noisy data are automatically smoothed. Our numerical examples with huge data sets for synthetic data as well as some real-world data confirm the efficiency of the methods, show the high quality of the spline approximation, and illustrate that the rendered iso-surfaces inherit a visual smooth appearance from the volume approximating splines.Item Topological Construction and Visualization of Higher Order 3D Vector Fields(The Eurographics Association and Blackwell Publishing, Inc, 2004) Weinkauf, Tino; Theisel, Holger; Hege, Hans-Christian; Seidel, Hans-PeterWe present the first algorithm for constructing 3D vector fields based on their topological skeleton. The skeleton itself is modeled by interactively moving a number of control polygons. Then a piecewise linear vector field is automatically constructed which has the same topological skeleton as modeled before. This approach is based on a complete segmentation of the areas around critical points into sectors of different flow behavior. Based on this, we present the first approach to visualizing higher order critical points of 3D vector fields.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Line and Curve Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and RealismItem Hardware-Accelerated Rendering of Photo Hulls(The Eurographics Association and Blackwell Publishing, Inc, 2004) Li, Ming; Magnor, Marcus; Seidel, Hans-PeterThis paper presents an efficient hardware-accelerated method for novel view synthesis from a set of images or videos. Our method is based on the photo hull representation, which is the maximal photo-consistent shape. We avoid the explicit reconstruction of photo hulls by adopting a view-dependent plane-sweeping strategy. From the target viewpoint slicing planes are rendered with reference views projected onto them. Graphics hardware is exploited to verify the photo-consistency of each rasterized fragment. Visibilities with respect to reference views are properly modeled, and only photo-consistent fragments are kept and colored in the target view. We present experiments with real images and animation sequences. Thanks to the more accurate shape of the photo hull representation, our method generates more realistic rendering results than methods based on visual hulls. Currently, we achieve rendering frame rates of 2-3 fps. Compared to a pure software implementation, the performance of our hardware-accelerated method is approximately 7 times faster.Categories and Subject Descriptors (according to ACM CCS): CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.Item Spherical Harmonic Gradients for Mid-Range Illumination(The Eurographics Association, 2004) Annen, Thomas; Kautz, Jan; Durand, Frédo; Seidel, Hans-Peter; Alexander Keller and Henrik Wann JensenSpherical harmonics are often used for compact description of incident radiance in low-frequency but distant lighting environments. For interaction with nearby emitters, computing the incident radiance at the center of an object only is not sufficient. Previous techniques then require expensive sampling of the incident radiance field at many points distributed over the object. Our technique alleviates this costly requirement using a first-order Taylor expansion of the spherical-harmonic lighting coefficients around a point. We propose an interpolation scheme based on these gradients requiring far fewer samples (one is often sufficient). We show that the gradient of the incident-radiance spherical harmonics can be computed for little additional cost compared to the coefficients alone. We introduce a semi-analytical formula to calculate this gradient at run-time and describe how a simple vertex shader can interpolate the shading. The interpolated representation of the incident radiance can be used with any low-frequency light-transfer technique.Item Connectivity Transformation for Mesh Metamorphosis(The Eurographics Association, 2004) Ahn, Minsu; Lee, Seungyong; Seidel, Hans-Peter; Roberto Scopigno and Denis ZorinIn previous mesh morphing techniques, the vertex set and connectivity of an in-between mesh are fixed and only the vertex positions are interpolated between input meshes. With this restriction, to accurately represent both source and target shapes, an in-between mesh should contain a much larger number of vertices than input meshes. This paper proposes a novel approach for mesh morphing, which includes connectivity changes in a metamorphosis. With the approach, an in-between mesh contains only the vertices from the input meshes and so the in-between vertex count does not exceed the sum of source and target vertex counts. The connectivity changes are realized by a sequence of edge swap operations, determined by considering the geometric errors from the input meshes. Experimental results demonstrate that the proposed approach generates almost same in-between shapes as the metamesh-based approach with a much smaller number of vertices.