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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 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 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 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.Item Multi-dimensional Reduction and Transfer Function Design using Parallel Coordinates(The Eurographics Association, 2010) Zhao, Xin; Kaufman, Arie; Ruediger Westermann and Gordon KindlmannMulti-dimensional transfer functions are widely used to provide appropriate data classification for direct volume rendering. Nevertheless, the design of a multi-dimensional transfer function is a complicated task. In this paper, we propose to use parallel coordinates, a powerful tool to visualize high-dimensional geometry and analyze multivariate data, for multi-dimensional transfer function design. This approach has two major advantages: (1) Combining the information of spatial space (voxel position) and parameter space; (2) Selecting appropriate highdimensional parameters to obtain sophisticated data classification. Although parallel coordinates offers simple interface for the user to design the high-dimensional transfer function, some extra work such as sorting the coordinates is inevitable. Therefore, we use a local linear embedding technique for dimension reduction to reduce the burdensome calculations in the high dimensional parameter space and to represent the transfer function concisely. With the aid of parallel coordinates, we propose some novel high-dimensional transfer function widgets for better visualization results. We demonstrate the capability of our parallel coordinates based transfer function (PCbTF) design method for direct volume rendering using CT and MRI datasets.Item Advanced Light Material Interaction for Direct Volume Rendering(The Eurographics Association, 2010) Lindemann, Florian; Ropinski, Timo; Ruediger Westermann and Gordon KindlmannIn this paper we present a heuristic approach for simulating advanced light material interactions in the context of interactive volume rendering. In contrast to previous work, we are able to incorporate complex material functions, which allow to simulate reflectance and scattering. We exploit a common representation of these material properties based on spherical harmonic basis functions, to combine the achieved reflectance and scattering effects with natural lighting conditions, i. e., incorporating colored area light sources. To achieve these goals, we introduce a modified SH projection technique, which is not just tailored at a single material category, but adapts to the present material. Thus, reflecting and scattering materials as assigned trough the transfer function can be captured in a unified approach. We will describe the required extensions to the standard volume rendering integral and present an approximation which allows to realize the material effects in order to achieve interactive frame rates. By exploiting a combination of CPU and GPU processing, we are able to modify material properties and can change the illumination conditions interactively. We will demonstrate the outcome of the proposed approach based on renderings of real-world data sets and report the achieved computation times.Item Stroke Matching for Paint Dances(The Eurographics Association, 2010) Colton, Simon; Pauline Jepp and Oliver DeussenWe have implemented a non-photorealistic rendering system which simulates the placement of paint/pencil/pastel strokes to produce representational artworks from digital images. The system is able to record an image of each paint stroke independent of the overall picture, in addition to some details about each stroke. Working with sets of paint strokes from paintings of different images, we investigate how to determine which stroke from one picture most closely resembles a given stroke from another picture. This enables the paint strokes from one picture to be used to paint a different painting. This further enables the animation of one picture morphing into another, as the paint strokes move and rotate into new positions and orientations. Using a K-means clustering approach, we can extract a set of representative strokes from a series of paintings/drawings, and animate the same set of strokes moving around a picture in order to represent different scenes at different times. We call such animations paint dances .We apply this technique to sets of portraits and we present the resulting paint dances in an artistic context as video art. We describe here the various methods we experimented with in order to determine an optimal stroke matching and extraction approach.Item Procedural Generation of Surface Detail for Science Fiction Spaceships(The Eurographics Association, 2010) Kinnear, Kate; Kaplan, Craig S.; Pauline Jepp and Oliver DeussenProcedural modelling can be used to generate digital content such as 3D digital models programmatically. In computer graphics, Procedural modelling has focused primarily on natural scenery and cityscapes. This paper considers the use of procedural modelling in a new domain: science fiction spaceships. We examine aesthetic principles as they relate to the beauty and visual interest of spaceships, especially surface details, and determine how these principles can be applied in a practical procedural modelling algorithm.We describe a prototype system that synthesizes and distributes surface details on large-scale spaceships. Given a surface representing the frame of a spaceship, we distribute geometry automatically in a coherent manner to achieve a characteristic science fiction aesthetic.Item A Virtual Tour of the Walls of Nicosia: An Assessment of Children's Experience and Learning Performance(The Eurographics Association, 2010) Michael, Despina; Zaharias, Panagiotis; Chrysanthou, Yiorgos; Alessandro Artusi and Morwena Joly and Genevieve Lucet and Denis Pitzalis and Alejandro RibesModern-day museums employ technologically advanced methods and equipment to facilitate the dissemination of information and education of their visitors. Such a system is installed at the Leventis Municipal Museum in Nicosia. An interactive application that runs on a multi-touch table allows the user to navigate through a 3D representation of the fortifications of Nicosia in different historical periods. In this paper, we assess the visitors' experience and learning performance/effectiveness using this system. We compare the results with those achieved using a traditional method, which is by studying printed maps exhibited at the same museum. We performed this comparison with a user study, involving two groups of children, each using one of the two different methods. Results show that users enjoy using the system and that their learning performance is much higher than that of the traditional method.