WSCG 2013: Full Papers Proceedings
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Item Interactive Radial Volume Histogram Stacks for Visualization of Kidneys from CT and MRI(Václav Skala - UNION Agency, 2013) Selver, M. Alper; Merve, Özdemir; Selvi, Eşref; Oliviera, Manuel M.; Skala, VáclavOptical parameter assignment via Transfer Functions (TF) is the sole interactive part in medical visualization via volume rendering. Being an interactive element of the rendering pipeline, TF specification has very important effects on the quality of volume-rendered medical images. However, TF specification should be supported by informative search spaces, interactive data exploration tools and intuitive user interfaces. Due to the trade-off between user control and TF domain complexity, integrating different features into the TF without losing user interaction is a challenging task since both are needed to fulfill the expectations of a physician. By addressing this problem, we introduce a semi-automatic method for initial generation of TFs. The proposed method extends the concept of recently introduced Volume Histogram Stack (VHS), which is a new domain constructed by aligning the histograms of the image slices of a CT and/or MR series. In this study, the VHS concept is extended by allowing the user to define an alignment axis using orthogonal multi planar reconstructions via simple, yet effective, interaction mechanisms. The construction of VHS according to the slices generated specifically for user defined search space allows the more informative integration of local intensity distribution, and better spatial positioning of the organ of interest into the TF. For testing, the proposed strategy is applied to kidney visualization from CT and MRI series. The performance of extended VHS domain is evaluated via intensity based TF design. Volumetric histogram based manual TF specifications are quantitatively compared to VHS based manual tweaking of original slices, and to extended-VHS based automatic TF design. The results show both quantitatively and qualitatively enhanced rendering quality for kidney visualization.
Item Methodology for Estimation of Tissue Noise Power Spectra in Iteratively Reconstructed MDCT Data(Václav Skala - UNION Agency, 2013) Walek, Petr; Jan, Jiří; Ouředníček, Petr; Skotáková, Jarmila; Jíra, Igor; Oliviera, Manuel M.; Skala, VáclavIterative reconstruction algorithms have been recently introduced into X-ray computed tomography imaging. Enabling patient dose reduction by up to 70% without affecting image quality they deserve attention; therefore properties of noise present in iteratively reconstructed data should be examined and compared to the images reconstructed by conventionally used filtered back projection. Instead of evaluating noise in imaged phantoms or small homogeneous regions of interest in real patient data, a methodology for assessing the noise in full extent of real patient data and in diverse tissues is presented in this paper. The methodology is based on segmentation of basic tissues, subtraction of images reconstructed by different algorithms and computation of standard deviation and radial onedimensional noise power spectra. Tissue segmentation naturally introduces errors into estimation of noise power spectra; therefore, magnitude of segmentation error is examined and is considered to be acceptable for estimation of noise power spectra in soft tissue and bones. As a result of this study it can be concluded that iDose4 hybrid iterative reconstruction algorithm effectively reduces noise in multidetector X-ray computed tomography (MDCT) data. The MDCT noise has naturally different characteristics in diverse tissues; thus it is object dependent and phantom studies are therefore unable to reflect its whole complexity.Item Deformation by discrete elastica(Václav Skala - UNION Agency, 2013) Bertini, Flavio; Morigi, Serena; Oliviera, Manuel M.; Skala, VáclavModeling a physically plausible deformation of a flexible object from its naturally planar (curved) state is a fun- damental and challenging topic in digital surface processing with applications to computer animation and game design. We propose a new variational model for detail preserving surface-based deformation of a body based on total curvature energy. We demonstrate the efficacy of the model with several examples which enhance the realism of the deformation.Item Handling haptics as a stand-alone medium(Václav Skala - UNION Agency, 2013) Moustakas, Konstantinos; Oliviera, Manuel M.; Skala, VáclavThis paper provides an information theoretic perspective of haptic rendering that aims to formulate the necessary theoretical foundations to lead to a compact and holistic representation of haptic media. Initially, an information theoretic view on haptic rendering is presented that enables the development of metrics enabling measuring of haptic information. Following the principles of information theory, two novel haptic information rendering pipelines are provided. Moreover, several quantities like entropy, mutual information and filters are defined and instantiated for the case of haptic rendering. Explicit examples of their potential use are analyzed. The paper concludes with examples and a discussion on how information theory can be used to provide a holistic haptic media representation scheme that can be used in a variety of application including coding, indexing and rendering of stand-alone haptic media.Item Using Image Quality Assessment to Test Rendering Algorithms(Václav Skala - UNION Agency, 2013) Amann, Julian; Weber, Bastian; Wüthrich, Charles A.; Oliviera, Manuel M.; Skala, VáclavTesting rendering algorithms is time intensive. New renderings have to be compared to reference renderings whenever a change is introduced into the render system. To speed up the test process, unit testing can be applied. However, detecting differences at the pixel level does not provide a sufficient criterion for the tests. For instance, in the context of games or scientific visualization, we are often faced with random procedurally generated geometry like e.g. particle systems, waving water, plants or molecules. Therefore, a more sophisticated approach than a pixelwise comparison is needed. We propose a Smart Image Quality Assessment algorithm (SIQA) based on a self-organizing map which can handle random scene elements. We compare our method with traditional image quality assessment methods like Mean Squared Error (MSE), Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Maps (SSIM). The proposed method helps to prevent the detection of images being categorized wrongly as correct or having errors, and ultimately helps saving time and increases productivity in the context of a test-driven development process for rendering algorithms.Item Adaptive Surface Reconstruction for SPH using 3-Level Uniform Grids(Václav Skala - UNION Agency, 2013) Akinci, Gizem; Akinci, Nadir; Oswald, Edgar; Teschner, Matthias; Oliviera, Manuel M.; Skala, VáclavThe marching cubes algorithm is a popular method for constructing surfaces from SPH data sets. In order to preserve all of the surface details in high curvature regions and to prevent potential temporal coherence artifacts, the resolution of the underlying uniform MC grid should be set up sufficiently high. However, this requirement unnecessarily increases the resolution in relatively flat regions where the surface can be constructed with lower resolutions without changing the quality. Accordingly, excessive number of triangles are generated, the memory consumption increases dramatically, and the performance decreases. In this paper, we present a 3-level grid structure which adapts its cells according to the curvature of the fluid surface. In contrast to widely-used octrees, we propose a simple to construct yet efficient hierarchical uniform grid structure. Mesh blocks from different resolution cells are seamlessly stitched by closing cracks with new triangles which establish only 0.15% to 0.6% of overall number of triangles in average. Experiments show that in contrast to the single level low resolution uniform grid approach, the presented method reconstructs fine details properly with a comparable performance; while it produces similar results with less number of triangles, up to four times better memory consumption and up to 60% better performance when compared to the single level high resolution uniform grid approach.Item Representing Feature Location Uncertainties in Spherical Images(Václav Skala - UNION Agency, 2013) Krolla, Bernd; Bleser, Gabriele; Cui, Yan; Stricker, Didier; Oliviera, Manuel M.; Skala, VáclavPose uncertainty estimation of calibrated cameras is a common task in the field of computer vision and uses location uncertainties of image features. For spherical cameras, those uncertainties cannot be optimally described using conventional latitude-longitude representation. Increasing distortions close to the poles of the spherical coordinate system prevent a suitable description through Gaussians. To overcome this limitation, we present a consistent location uncertainty representation for spherical image features: Our approach is based on normal vectors in Cartesian space and applicable to any kind of camera with convex projection surfaces, such as catadioptric and spherical systems. We compare its performance against latitude-longitude representation by estimating camera pose uncertainties through first order error propagation in a weighted least squares pose estimation scenario. Our experiments on synthetic and real data show that the proposed approach delivers consistent results outperforming conventional latitude-longitude representation.Item Semi-Automatic Synthesis of Videos of Performers Appearing to Play User-Specified Music(Václav Skala - UNION Agency, 2013) Yamamoto, Tomohiro; Okabe, Makoto; Hijikata, Yusuke; Onai, Rikio; Oliviera, Manuel M.; Skala, VáclavWe propose a method to synthesize the video of a user-specified band music, in which the performers appear to play it nicely. Given the music and videos of the band members as inputs, our system synthesizes the resulting video by semi-automatically cutting and concatenating the videos temporarily so that these synchronize to the music. To compute the synchronization between music and video, we analyze the timings of the musical notes of them, which we estimate from the audio signals by applying techniques including short-time Fourier transform (STFT), image processing, and sound source separation. Our video retrieval technique then uses the estimated timings of musical notes as the feature vector. To efficiently retrieve a part of the video that matches to a part of the music, we develop a novel feature matching technique more suitable for our feature vector than dynamic-time warping (DTW) algorithm. The output of our system is the project file of Adobe After Effects, on which the user can further refine the result interactively. In our experiment, we recorded videos of performances of playing the violin, piano, guitar, bass and drums. Each video is recorded independently for each instrument. We demonstrate that our system helps the non-expert performers who cannot play the music well to synthesize its performance videos. We also present that, given an arbitrary music as input, our system can synthesize its performance video by semi-automatically cutting and pasting existing videos.Item Single view single light multispectral object segmentation(Václav Skala - UNION Agency, 2013) Schick, Eduard; Herbort, Steffen; Grumpe, Arne; Wöhler, Christian; Oliviera, Manuel M.; Skala, VáclavIn this paper we present an approach for the acquisition and segmentation of spectral Bidirectional Reflectance Distribution Function (BRDF) measurements of real-world objects. The acquisition setup is a priori fully calibrated and provides pixel-synchronous image and depth data of the examined objects. Based on one single viewing and illumination geometry, we are able to determine spectrally distinct surface regions for objects with abruptly changing surface materials (painted surface patches) and for objects with gradually changing materials (partially oxidized iron). For clustering we apply the k-means algorithm and the mean-shift algorithm. The segmented clusters are used to adapt individual spectral BRDFs (Lambert, Phong, Cook-Torrance) to the obtained cluster data. Additionally, the elemental abundances of iron and rust on a metal surface are analyzed using spectral unmixing. The paper presents a detailed discussion of our method and provides critical insight into the obtained results.Item Robust and Scalable Navmesh Generation with multiple levels and stairs support(Václav Skala - UNION Agency, 2013) Saupin, Guillaume; Roussel, Olivier; Le Garrec, Jeremie; Oliviera, Manuel M.; Skala, VáclavAutomatically planning motion for robots or humans in a virtual environment is a complex task. The navigation cannot be done directly on the geometric scene. An internal representation of the environment is necessary. However, virtual environments complexity is growing at an important rate, and it is not unusual to work with millions of triangles and area as large as some square kilometers. In these cases, grid based methods require too much memory, and are too slow for A* algorithms. Polygons based methods are more memory and computation efficient, but they are difficult to generate and require complex preprocessing of the input mesh to ensure nice topological properties. In this paper, we propose an hybrid method, which uses 3D voxelization to generate a clean polygon mesh simple enough to perform fast A* search. Using this approach, we robustly generate Navigation Meshes for large environments with fine details, described by millions of triangles, without any assumption on the quality of the input mesh. The input mesh can contains holes, degenerated or intersecting triangles.Item Haptic Technique for Simulating Multiple Density Materials and Material Removal(Václav Skala - UNION Agency, 2013) Bogoni, Tales Nereu; Pinho, Márcio Sarroglia; Oliviera, Manuel M.; Skala, VáclavThe term haptic refers to the tactile sensation perceived by the user when he is manipulating objects in a Virtual Environment. These sensations are extremely important in Virtual Reality simulators for training medical and dental procedures with the goal of increasing the level of motor skills. Many tasks trained, such as teeth and bones drilling, are held in rigid bodies and require parts of the virtual models to be removed. One way to manipulate these objects is by using voxel-based models, which divide the object into smaller parts that can be removed by the haptic device. This paper deals with a new method for haptic rendering with voxel-based rigid bodies that may be composed of various materials with different densities. The method describes the process for obtaining and storing the virtual objects. In addition it details the techniques used for collision detection, calculating the force feedback and removing parts of objects during the drilling process. The paper ends with an experiment that shows that the method provides stability, supports removal of voxels and different material densities properly.Item Computational Celtic Canvas for Zoomorphs and Knotworks(Václav Skala - UNION Agency, 2013) Doyle, Richard B; Semwal, S. K.; Oliviera, Manuel M.; Skala, VáclavThis paper presents Celtic Canvas -- a framework towards computationally generating patterns similar to simple Celtic artwork. As Celtic patterns are highly structured, a robust model of curvature dynamics is introduced in the paper to allow the evolution of space curves as a foundation for line drawing and structural anatomy. Cellular automata integrates several features including -- lines and forms, allocation of space, a solution of crossing states, the occlusion processing, depth cues, and line weighing. Lattice gas automata assist in generating varying width patterns. Original digitally available artwork provides shapes and forms as line-art. Our novel contribution is that we are successful in generating examples of knotwork and zoomorphs (animal designs shapes) that mimic the characteristics of the Celtic art forms. Future research areas are also identified.Item A segmentation method for nuclei identification from sagittal images of Drosophila melanogaster embryos(Václav Skala - UNION Agency, 2013) de Sousa, Daniela Justiniano; Arruda Cardoso, Maria; Bisch, Paulo Mascarello; Pereira Lopes, Francisco José; Nassif Travençolo, Bruno Augusto; Oliviera, Manuel M.; Skala, VáclavThis paper proposes a segmentation method for sagittal images obtained from Drosophila melanogaster embryos at early stages of development. The proposed method operates in the spatial domain and uses traditional filters and segmentation techniques for image processing. However, one common problem encountered after the segmentation of sagittal images is the merged nuclei. In order to split these nuclei, our approach uses the curvature of the shape of the merged nuclei to find the regions of division between the nuclei. The proposed method was compared to other techniques and it achieved better results. In general, the obtained results have shown good performance and were able to identify individual nuclei, providing an efficient and accurate solution for segmentation of nuclei in images obtained from the sagittal plane of Drosophila embryos.Item Analysis of Interactive Editing Operations for Out-of-Core Point-Cloud Hierarchies(Václav Skala - UNION Agency, 2013) Scheiblauer, Claus; Wimmer, Michael; Oliviera, Manuel M.; Skala, VáclavIn this paper we compare the time and space complexity of editing operations on two data structures which are suitable for visualizing huge point clouds. The first data structure was introduced by Scheiblauer andWimmer [SW11] and uses only the original points from a source data set for building a level-of-detail hierarchy that can be used for rendering points clouds. The second data structure introduced byWand et al. [WBB+07] requires additional points for the level-of-detail hierarchy and therefore needs more memory when stored on disk. Both data structures are based on an octree hierarchy and allow for deleting and inserting points. Besides analyzing and comparing these two data structures we also introduce an improvement to the points deleting algorithm for the data structure of Wand et al. [WBB+07], which thus allows for a more efficient node loading strategy during rendering.Item Interactive Grass Rendering Using Real-Time Tessellation(Václav Skala - UNION Agency, 2013) Jahrmann, Klemens; Wimmer, Michael; Oliviera, Manuel M.; Skala, VáclavGrass rendering is needed for many outdoor scenes, but for real-time applications, rendering each blade of grass as geometry has been too expensive so far. This is why grass is most often drawn as a texture mapped onto the ground or grass patches rendered as transparent billboard quads. Recent approaches use geometry for blades that are near the camera and flat geometry for rendering further away. In this paper, we present a technique which is capable of rendering whole grass fields in real time as geometry by exploiting the capabilities of the tessellation shader. Each single blade of grass is rendered as a two-dimensional tessellated quad facing its own random direction. This enables each blade of grass to be influenced by wind and to interact with its environment. In order to adapt the grass field to the current scene, special textures are developed which encode on the one hand the density and height of the grass and on the other hand its look and composition.Item A generic topological framework for physical simulation(Václav Skala - UNION Agency, 2013) Fléchon, Elsa; Zara, Florence; Damiand, Guillaume; Jaillet, Fabrice; Oliviera, Manuel M.; Skala, VáclavThis paper presents the use of a topological model to simulate a soft body deformation based on a Mass-Spring System. We provide a generic framework which can integrate any kind of geometrical meshes (hexahedral or tetrahedral elements), using several numerical integration schemes (Euler semi-implicit or implicit). This framework naturally allows topological changes in the simulated object during the animation. Our model is based on the 3D Linear Cell Complex topological model (itself based on a 3D combinatorial map), adding the extra information required for simulation purposes. Moreover, we present some adaptations performed on this data structure to fit our simulation requirements, and to allow efficient cutting or piercing in a 3D object.Item Influence of Dynamic Wrinkles on the Perceived Realism of Real-Time Character Animation(Václav Skala - UNION Agency, 2013) Alcon, Javier; Travieso, David; Larboulette, Caroline; Oliviera, Manuel M.; Skala, VáclavWhen creating a real-time character animation (e.g. for video games), fine grain details such as cloth wrinkles are very often omitted due to the limitation of available resources. However, we believe that they are crucial to increase realism, hence user immersion. In this paper, we present a perceptual study of dynamic wrinkles on clothes to show that they indeed have an important impact on realism. The models, animations and textures we used are game realistic and the wrinkling algorithm is fast enough to be used in a game. We have found that parameters influencing the perception of dynamic wrinkles include movement type and speed, viewing angle, and texture colors. Our results should be useful for animators or game designers to help them add wrinkles only where they are necessary, and activate them only when they have an impact on realism.Item BRDF Reconstruction Using Compressive Sensing(Václav Skala - UNION Agency, 2013) Seylan, Nurcan; Ergun, Serkan; Öztürk, Aydın; Oliviera, Manuel M.; Skala, VáclavCompressive sensing is a technique for efficiently acquiring and reconstructing the data. This technique takes advantage of sparseness or compressibility of the data, allowing the entire measured data to be recovered from relatively few measurements. Considering the fact that the BRDF data often can be highly sparse, we propose to employ the compressive sensing technique for an efficient reconstruction. We demonstrate how to use compressive sensing technique to facilitate a fast procedure for reconstruction of large BRDF data. We have showed that the proposed technique can also be used for the data sets having some missing measurements. Using BRDF measurements of various isotropic materials, we obtained high quality images at very low sampling rates both for diffuse and glossy materials. Similar results also have been obtained for the specular materials at slightly higher sampling rates.Item Cartographic Rendering of Elevation Surfaces using Procedural Contour Lines(Václav Skala - UNION Agency, 2013) Manya, Neha; Ayyala, Isaac; Benger, Werner; Oliviera, Manuel M.; Skala, VáclavWe describe a method to render a height field given on a triangular mesh in a manner that is similar to wellknown cartographic map views. This approach utilizes hypsometric tints and creates topographic contour lines procedurally as part of the rendering process. We discuss essential graphical enhancement techniques such as line smoothing, gradient compensation, contour line visibility fading, nonlinear elevation mapping, and shininess variation. The method is exemplified upon various numerical data sets from application sciences, demonstrating its ability to visually allow quantitative and qualitative precise assessment of the data values.Item Efficient complementary viewpoint selection in volume rendering(Václav Skala - UNION Agency, 2013) Grau, Sergi; Puig, Anna Sergio; Amorós, Oscar; Oliviera, Manuel M.; Skala, VáclavA major goal of visualization is to appropriately express knowledge of scientific data. Generally, gathering visual information contained in the volume data often requires a lot of expertise from the final user to setup the parameters of the visualization. One way of alleviating this problem is to provide the position of inner structures with different viewpoint locations to enhance the perception and construction of the mental image. To this end, traditional illustrations use two or three different views of the regions of interest. Similarly, with the aim of assisting the users to easily place a good viewpoint location, this paper proposes an automatic and interactive method that locates different complementary viewpoints from a reference camera in volume datasets. Specifically, the proposed method combines the quantity of information each camera provides for each structure and the shape similarity of the projections of the remaining viewpoints based on Dynamic Time Warping. The selected complementary viewpoints allow a better understanding of the focused structure in several applications. Thus, the user interactively receives feedback based on several viewpoints that helps him to understand the visual information. A live-user evaluation on different data sets show a good convergence to useful complementary viewpoints.
