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Item Improving Shadow Map Filtering with Statistical Analysis(The Eurographics Association, 2011) Gumbau, Jesus; Szirmay-Kalos, László; Sbert, Mateu; Sellés, Miguel Chover; N. Avis and S. LefebvreShadow maps are widely used in real-time applications. Shadow maps cannot be filtered linearly as regular textures, thus undersampling leads to severe aliasing. This problem has been attacked by methods that transform the depth values to allow approximate linear filtering and to approaches based on statistical analysis, which suffer from light bleeding artifacts. In this paper we propose a new statistical filtering method for shadow maps, which approximates the cumulative distribution function (CDF) of depths with a power function. This approximation significantly reduces light bleeding artifacts, maintaining performance and spatial costs. Like existing techniques, the algorithm is easy to implement on the graphics hardware and is fairly scalable.Item JustDrawIt: A 3D Sketching System(The Eurographics Association, 2012) Grimm, Cindy; Joshi, Pushkar; Karan Singh and Levent Burak KaraWe present ''JustDrawIt'', a sketch-based system for creating 3D curves suitable for surfacing. The user can sketch in a free-form manner from any view at any time, and the system infers how those sketch strokes should be added to the drawing. Specifically, existing curves are projected to 2D and analyzed to see if the stroke edits or extends an existing curve, or if the stroke should make a new curve. In the former case the 2D stroke is promoted to 3D using the position of the existing curve, and then joined to that curve. In the latter case, we use additional spatial information (e.g. temporary 3D surfaces) to create a new curve in 3D. All non-sketching interactions are based on unintrusive context-aware, in-screen pie menus designed for rapid pen-based input. We also provide novel rendering styles and aides for interpreting and working with 3D sketches. Finally, we support snapping together curve networks and specifying normals in order to create surface models.Item Two Examples of GPGPU Acceleration of Memory-intensive Algorithms(The Eurographics Association, 2010) Marras, Stefano; Mura, Claudio; Gobbetti, Enrico; Scateni, Riccardo; Scopigno, Roberto; Enrico Puppo and Andrea Brogni and Leila De FlorianiThe advent of GPGPU technologies has allowed for sensible speed-ups in many high-dimension, memory-intensive computational problems. In this paper we demonstrate the e ectiveness of such techniques by describing two applications of GPGPU computing to two di erent subfields of computer graphics, namely computer vision and mesh processing. In the first case, CUDA technology is employed to accelerate the computation of approximation of motion between two images, known also as optical flow. As for mesh processing, we exploit the massivelyparallel architecture of CUDA devices to accelerate the face clustering procedure that is employed in many recent mesh segmentation algorithms. In both cases, the results obtained so far are presented and thoroughly discussed, along with the expected future development of the work.Item Evaluation of 3D Interest Point Detection Techniques(The Eurographics Association, 2011) Dutagaci, Helin; Cheung, Chun Pan; Godil, Afzal; H. Laga and T. Schreck and A. Ferreira and A. Godil and I. Pratikakis and R. VeltkampIn this paper, we compare the results of five 3D interest point detection techniques to the interest points marked by human subjects. This comparison is used to quantitatively evaluate the interest point detection algorithms. We asked human subjects to look at a number of 3D models, and mark interest points on the models via a web-based interface. We propose a voting-based method to construct ground truth out of humans' selections of interest points. Evaluation measures, namely False Positive and False Negative Errors, are then defined based on the geodesic distance between the interest points detected by a particular algorithm and the human-generated ground truth.Item A Geometry-Shader-Based Adaptive Mesh Refinement Scheme Using Semiuniform Quad/ Triangle Patches and Warping(The Eurographics Association, 2010) Knuth, Martin; Kohlhammer, Jörn; Kuijper, Arjan; Kenny Erleben and Jan Bender and Matthias TeschnerIn the field of garment simulation the resolution of the simulation mesh has a direct impact on visual quality. Unfortunately, an increase in mesh resolution introduces a much higher computational cost and potentially causes instability inside the simulation. In addition, it increases the amount of data sent to the renderer for visualisation. Therefore, a GPU-based refinement of the simulated mesh has several advantages, since all additional data is generated immediately before rendering. This allows an increase in visual quality without adding to computational costs for the simulation process or bandwidth necessary for rendering. In this paper we present a view-dependent, adaptive tessellation method designed for the geometry processing stage of modern GPUs. It uses uniform meshes internally, removing the necessity to store external patches. Since we deal with a local refinement scheme, sudden changes in the mesh structure size on adjacent patches may occur incidentally. To reduce this effect as far as possible, we control the triangle density distribution of the refinement process inside a refined triangle patch.Item FreeCam: A Hybrid Camera System for Interactive Free-Viewpoint Video(The Eurographics Association, 2011) Kuster, Claudia; Popa, Tiberiu; Zach, Christopher; Gotsman, Craig; Gross, Markus; Peter Eisert and Joachim Hornegger and Konrad PolthierWe describe FreeCam - a system capable of generating live free-viewpoint video by simulating the output of a virtual camera moving through a dynamic scene. The FreeCam sensing hardware consists of a small number of static color video cameras and state-of-the-art Kinect depth sensors, and the FreeCam software uses a number of advanced GPU processing and rendering techniques to seamlessly merge the input streams, providing a pleasant user experience. A system such as FreeCam is critical for applications such as telepresence, 3D video-conferencing and interactive 3D TV. FreeCam may also be used to produce multi-view video, which is critical to drive newgeneration autostereoscopic lenticular 3D displays.Item On Expert Performance in 3D Curve-Drawing Tasks(The Eurographics Association, 2009) Schmidt, Ryan; Khan, Azam; Kurtenbach, Gord; Singh, Karan; Cindy Grimm and Joseph J. LaViola, Jr.A study is described which examines the drawing accuracy of experts when drawing foreshortened projections of 3D curves in ecologically-valid conditions. The main result of this study is that the distribution of error in expert drawings exhibits a bias similar to that previously observed in non-expert subjects, which is dependent on the degree of foreshortening of the imagined drawing surface. A review of existing perceptual studies also finds that only absolute 2D image-space error has been considered, which has been found to be largest with viewing angles of 25-55. Our visualizations of 3D error indicate that 3D bias continues to increase with decreasing viewing angle. Based on these findings, we analyze current 3D curve drawing techniques for susceptibility to foreshortening bias, and make some suggestions for future sketch-based modeling systems.Item Efficient Acquisition and Clustering of Local Histograms for Representing Voxel Neighborhoods(The Eurographics Association, 2010) Meß, Christian; Ropinski, Timo; Ruediger Westermann and Gordon KindlmannIn the past years many interactive volume rendering techniques have been proposed, which exploit the neighboring environment of a voxel during rendering. In general on-the-fly acquisition of this environment is infeasible due to the high amount of data to be taken into account. To bypass this problem we propose a GPU preprocessing pipeline which allows to acquire and compress the neighborhood information for each voxel. Therefore, we represent the environment around each voxel by generating a local histogram (LH) of the surrounding voxel densities. By performing a vector quantization (VQ), the high number of LHs is than reduced to a few hundred cluster centroids, which are accessed through an index volume. To accelerate the required computational expensive processing steps, we take advantage of the highly parallel nature of this task and realize it using CUDA. For the LH compression we use an optimized hybrid CPU/GPU implementation of the k-means VQ algorithm. While the assignment of each LH to its nearest centroid is done on the GPU using CUDA, centroid recalculation after each iteration is done on the CPU. Our results demonstrate the applicability of the precomputed data, while the performance is increased by a factor of about 10 compared to previous approaches.Item Developing a System of Screen-less Animation for Experiments in Perception of Movement(The Eurographics Association, 2012) MacGillivray, Carol; Mathez, B.; Leymarie, F. Fol; Douglas Cunningham and Donald HouseExperiments that test perceptual illusions and movement perception have relied predominantly on observing participant response to screen-based phenomena. There are a number of inherent problems to this experimental method as it involves flicker, ignores depth perception and bypasses the proprioceptive system, in short it is psychophysically distinct from dynamic real life (veridical) perception. Indeed there still is much disagreement regarding perception of apparent (screen- based) motion despite the fact that we view it in a myriad of ways on an everyday basis. With the aim of furthering our understanding and evaluation of veridical movement perception, the team sought to develop a replicable technique that included embodied, multi-sensory perception but eliminated the screen. They approached this by taking time-based techniques from animation and converting them to the spatial; grouping static objects according to Gestalt principles, to create sequential visual cues that, when lit with projected light, demand selective attention. This novel technique has been called the 'diasynchronic' technique and the system; the 'Diasynchronoscope'. The name Diasynchronoscope comes from combining diachronic, (the study of a phenomenon as it changes through time) with synchronous and scope (view). In being so named, it evokes the early animation simulators such as the phenakistoscope and the zoetrope, regarded as direct ancestors of the project in acting both as art objects and experimental media. This paper documents the creation of this new, experimental medium in choreographed time and discusses its potential as a novel tool for investigating aesthetics in movement.Item Suggestive Hatching(The Eurographics Association, 2010) Singh, Mayank; Schaefer, Scott; Pauline Jepp and Oliver DeussenWe present a method for drawing lines on an object that depict both the shape and shading of the object. To do so, we construct a gradient field of the diffuse intensity of the surface to guide a set of adaptively spaced lines. The shape of these lines reflect the lighting under which the object is being viewed and its shape. When the light source is placed at the viewer's location, these lines emanate from silhouettes and naturally extend Suggestive Contours. By using a hierarchical proximity grid, we can also improve the quality of these lines as well as control their density over the image. We also provide a method for detecting and removing ridge lines in the intensity field, which lead to artifacts in the line drawings.