Short Papers 2008

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https://diglib.eg.org/handle/10.2312/266

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Removing Artifacts Due To Frequency-Domain Processing of Light-Fields
(The Eurographics Association, 2008) Intwala, Chintan; Georgeiv, Todor; Katerina Mania and Eric Reinhard
In previous works, light-field capture has been analyzed in spatio-angular representation. A light-field camera samples the optical signal within a single photograph by multiplexing the 4D radiance onto the physical 2D surface of the sensor. Besides sampling the light field spatially, methods have been developed for multiplexing the radiance in the frequency domain by optically mixing different spatial and angular frequency components. The mathematical method for recovering the multiplexed spatial and angular information from the frequency representation is very straightforward. However, the results are prone to lots of artifacts due to limitations inherent to frequency-domain processing of images. In this paper, we try understand the characteristics of these artifacts. Furthermore, we study the effect and sources of artifacts that affect the quality of the results and present various methods for the removal of artifacts.
Measuring and Enhancing the Legibility of GPU-rendered Text
(The Eurographics Association, 2008) Tycowicz, Christoph von; Loviscach, Joern; Katerina Mania and Eric Reinhard
Whereas the rendering of tiny typefaces in 2D applications has been perfected over decades, the legibility of text in 3D visualizations has rarely been addressed. This affects road signs, meters, screens, and books in virtual reality applications ranging from car driving simulators to digital lecture halls. To improve text rendering and display, we devised a lightweight psychovisual test to measure one prominent aspect of legibility. We subjected promising GPU-based methods for crisp minification to this test. It turned out that legibility may be improved without undue costs. Not all techniques whose results look appealing on first sight will, however, enhance legibility.
Crowds in Context: Evaluating the Perceptual Plausibility of Pedestrian Orientations
(The Eurographics Association, 2008) Peters, Christopher; Ennis, Cathy; McDonnell, Rachel; O'Sullivan, Carol; Katerina Mania and Eric Reinhard
We describe a work-in-progress evaluating the plausibility of pedestrian orientations. While many studies have focused on creating accurate or fast crowd simulation models for populating virtual cities or other environments, little is known about how humans perceive the characteristics of generated scenes. Our initial study, reported here, consists of an evaluation based on static imagery reconstructed from annotated photographs, where the orientations of individuals have been modified. An important focus in our research is the consideration of the effects of the context of the scene on the evaluation, in terms of nearby individuals, objects and the constraints of the walking zone. This work could prove significant for improving and informing the creation of computer graphics pedestrian models. Our particular aim is to inform level-of-detail models
Adaptive Remeshing of Non-Manifold Surfaces
(The Eurographics Association, 2008) Zilske, Michael; Lamecker, Hans; Zachow, Stefan; Katerina Mania and Eric Reinhard
We present a unified approach for consistent remeshing of arbitrary non-manifold triangle meshes with additional user-defined feature lines, which together form a feature skeleton. Our method is based on local operations only and produces meshes of high regularity and triangle quality while preserving the geometry as well as topology of the feature skeleton and the input mesh.
Level of Detail Flow Simulation
(The Eurographics Association, 2008) Klar, Gergely; Katerina Mania and Eric Reinhard
In this paper we present a framework to simulate visually plausible large scale flow of fluids or smoke. To maintain real-time speed, we define the simulation over a coarse grid which is refined with a more detailed grid at places where fine details may emerge, like around moving obstacles. The detailed grids also act as fixed frames of reference to the surrounded obstacles to prevent the need for working with moving boundaries in the flow.
Efficient Spherical Harmonics Lighting with the Preetham Skylight Model
(The Eurographics Association, 2008) Habel, Ralf; Mustata, Bogdan; Wimmer, Michael; Katerina Mania and Eric Reinhard
We present a fast and compact representation of a skylight model for spherical harmonics lighting, especially for outdoor scenes. This representation allows dynamically changing the sun position and weather conditions on a per frame basis. We chose the most used model in real-time graphics, the Preetham skylight model, because it can deliver both realistic colors and dynamic range and its extension into spherical harmonics can be used to realistically light a scene. We separate the parameters of the Preetham skylight model s spherical harmonics extension and perform a polynomial two-dimensional non-linear least squares fit for the principal parameters to achieve both negligible memory and computation costs. Additionally, we execute a domain specific Gibbs phenomena suppression to remove ringing artifacts.
Knitty: 3D Modeling of Knitted Animals with a Production Assistant Interface
(The Eurographics Association, 2008) Igarashi, Yuki; Igarashi, Takeo; Suzuki, Hiromasa; Katerina Mania and Eric Reinhard
Knitty is an interactive design system for creating knitted animals. The user designs a 3D surface model using a sketching interface. The system automatically generates a knitting pattern and then visualizes the shape of the resulting 3D animal model by applying a simple physics simulation. The user can see the resulting shape before beginning the actual knitting. The system also provides a production assistant interface for novices. The user can easily understand how to knit each stitch and what to do in each step. In a workshop for novices, we observed that even children can design their own knitted animals using our system.
Efficient Soft Tissue Modelling Using Charged Particle Control Points
(The Eurographics Association, 2008) Buckley, Oliver; John, Nigel W.; Katerina Mania and Eric Reinhard
As the performance levels of personal computers increases so does the desire for more realistic and immersive software and simulation. An area where this is particularly the case is that of medical training simulation, where there is an increasing demand for high fidelity virtual environments. However, realistically modeling of soft tissue deformation still poses a considerable challenge especially when haptic feedback is required. This paper presents a new approach to soft tissue deformation using a novel Charged Particle method to control the haptic rendering while also adding a further level of realism by incorporating independent high resolution visualization to the simulation.
Physically-Based Interactive Sand Simulation
(The Eurographics Association, 2008) Pla-Castells, Marta; García-Fernandez, Ignacio; Martinez-Dura, Rafael J.; Katerina Mania and Eric Reinhard
The interactive simulation of 3D terrains has been approached from several perspectives. Due to the complexity of the system involved, most of the models proposed focus on a visually realistic animation of the scene, rather than on a physically-based accurate simulation of a granular system. Those models lack generality when interacting with the environment; in most cases, no reaction forces are computed, considering only soil deformation. This limitation reduces their usability in applications such as driving simulators. We propose the use of a theoretical discrete model that considers normal forces for 3D real-time simulation of granular systems. We also extend this model to consider horizontal forces, allowing a wider range of interactions. Several numerical tests have been implemented and detailed results have been analyzed which show a good model performance.
Post Facto Registration Tools for Urban Modelling
(The Eurographics Association, 2008) Morvan, Yann; Hinks, Tommy; Carr, Hamish; Laefer, Debra F.; O'Sullivan, Carol; Morrish, W. Sean; Katerina Mania and Eric Reinhard
Urban modelling applications require high-precision geometric models both for graphical rendering and for engineering purposes. While geometric models, photographic images and laser-scanned point clouds are ideally co-registered to national coordinate grids at the time of acquisition, the quantity and diversity of data sources means that registration must often be performed post facto. Moreover, the sheer size of urban point clouds prevents automated conversion and registration of the entire data set at once. We describe an interactive tool that manages the workflow for converting urban-scale point clouds to grid-registered geometric models. Our 'user in the loop' approach lets us leverage natural human understanding of the data to bypass issues of scale.
Microquad Soft Shadow Mapping Revisited
(The Eurographics Association, 2008) Schwarz, Michael; Stamminger, Marc; Katerina Mania and Eric Reinhard
Recently, real-time soft shadow research saw many important contributions from the class of soft shadow mapping algorithms, where approximate occluder geometry is reconstructed from a shadow map and backprojected onto the light source to determine its occlusion. An interesting approximation primitive is the microquad obtained from unprojected shadow map texel centers. However, its full potential has not yet been realized since correct clipping against the light and exact occlusion bitmask updates have previously been ignored motivated by performance considerations. In this paper, we first extend the microquad definition to also allow for triangles as micro-occluders. We then demonstrate how to determine the exact occlusion bitmask of a microquad with correct clipping.
Boolean Operations for Free-form Models Represented in Geometry Images
(The Eurographics Association, 2008) Fu, Yan; Zhou, Bingfeng; Katerina Mania and Eric Reinhard
We present a Boolean operation algorithm for free-form solid models represented in geometry images. By taking advantage of the regular data organization of geometry images, our algorithm can perform efficient surface division using boundary-fill algorithm which is previously used for digital image processing. A quadtree subdivision scheme is also applied to the geometry images to accelerate the intersection line calculation. Experimental result shows that the algorithm can generate well-defined closed triangle meshes for Boolean operations. The resulted triangle mesh can also be converted into a geometry image for further processing.
Rendering Method for Flat Origami
(The Eurographics Association, 2008) Mitani, Jun; Katerina Mania and Eric Reinhard
In flat Origami (Origami which is folded flat), some cases exist that have a closed-loop in the overlap order of faces after they are folded. It is difficult to display this shape correctly on the screen when Origami is expressed by sets of plane polygons of zero thickness as is generally used in CG because all faces are placed on the same plane. In the present paper, we propose a new rendering technique to solve this problem. In the proposed method, we prepare a matrix that represents the overlap relation between two faces and a face ID buffer, the concept of which is similar to a Z buffer in the z-buffer algorithm. With this buffer, the face located in the uppermost is monitored in each pixel at the rendering stage. We render the shape on the face ID buffer using a scanline algorithm and display the folded shape by outputting the result in which the edges are extracted. Moreover, we render the shape in technical illustration style by coloring each vertex according to the number of mountain and valley folds connected to the vertex. In addition, we propose a simple pseudo shading algorithm.
Compensation of the Light Attenuation with Depth of Images Captured by a Confocal Microscope Using a MRF Deformation Model and Graph Cuts
(The Eurographics Association, 2008) Capek, Martin; Michalek, Jan; Janacek, Jiri; Kubinova, Lucie; Hana, Karel; Smrcka, Pavel; Katerina Mania and Eric Reinhard
We study series of fluorescent optical sections, i.e. three-dimensional (3D) biomedical images, captured by a confocal laser scanning microscope (CLSM). Fluorescent image intensities of optical sections from deep layers of the specimen are often darker than intensities of sections from the top layers due to absorption and scattering of both excitation and fluorescent light. To solve this problem we apply a Markov Random Field (MRF) model including an efficient deformation model for tracking structures within the 3D images for computation of optical flow. We approach the corresponding optimization problem by the graph cuts. Image intensities of optical sections are recomputed according to the found optical flow, since the flow gives us evaluation of their proper brightness. Finally, the light attenuation with depth is compensated by matching accumulative histograms of optical sections of the original series with respect to optical sections improved by the optical flow. By this approach we obtain an algorithm that is less sensitive to changes of structures within series (especially to their enlargement and diminishing) than algorithms based purely on histogram matching, warping or equalization.
Revealing Pentimenti Through Raking Angle Photography
(The Eurographics Association, 2008) Cheung, Chi Yin; Mohan, Ankit; Tumblin, Jack; Katerina Mania and Eric Reinhard
Discovering hidden details in historical paintings, such as pentimenti, can help reveal historical influences and changing intentions of an artist. Top-down photographs of visible light historical paintings do not capture much of the finer surface detail on the object being photographed. We present a technique using only visible light photography with a specially constructed octagonal reflector to aid the discovery of hidden details in historical paintings, by measuring Fresnel reflectance effects through raking angle photography. We exploit the significantly higher reflectance of dielectric surfaces at low angles to reveal hidden details that are otherwise not visible through ordinary photography. We also present a way to explore the details both statically and interactively.
Mining Motifs from Human Motion
(The Eurographics Association, 2008) Meng, Jingjing; Yuan, Junsong; Hans, Mat; Wu, Ying; Katerina Mania and Eric Reinhard
Mining frequently occurring temporal motion patterns (motion motifs) is important for understanding, organizing and retrieving motion data. However, without any a priori knowledge of the motifs, such as their lengths, contents, locations and total number, it remains a challenging problem due to the enormous computational cost involved in analyzing huge motion databases. Moreover, since the same motion motif can exhibit different temporal and spatial variations, it prevents directly applying existing data mining methods to motion data. In this paper, we propose an efficient motif discovery method which can handle both spatial and temporal variations of motion data. We translate the motif discovery problem into finding continuous paths in a matching trellis, where each continuous path corresponds to an instance of a motif. A tree-growing method is introduced to search for the continuous paths constrained by a branching factor, and to accommodate intra-pattern variations of motifs. By using locality-sensitive hashing (LSH) to find the approximate matches and build the trellis, the overall complexity of our algorithm is only sub-quadratic to the size of the database, and is of linear memory cost. Experimental results on a data set of 32,260 frames show that our method can effectively discover meaningful motion motifs regardless of their spatial and temporal variations.
Volume Data Visualization Using Fractal Interpolation Surfaces
(The Eurographics Association, 2008) Manousopoulos, Polychronis; Drakopoulos, Vassileios; Theoharis, Theoharis; Katerina Mania and Eric Reinhard
Visualization of medical or experimental data is often achieved by extracting an intermediate geometric representation of the data. One such popular method for extracting an isosurface from volume data is the Marching Cubes (MC) algorithm, which creates a polygon mesh by sampling the data at the vertices of the cubes of a 3D grid. A method that uses the vertex extraction phase of the MC algorithm and represents the data by fractal interpolation surfaces (FISs) instead of a polygon mesh is presented. The proposed method is appropriate for isosurfaces that are not locally flat, such as natural structures. Another advantage is that a coarser grid resolution can typically be used, since FISs are particularly good at representing detailed, irregular or self-similar structures. Thus for many cases the resulting isosurface is more accurate or more compact. The multiresolution extension of the method is also straightforward. Experimental data verify the practical usefulness of the proposed method.
Evaluation of a Mobile MR Geovisualisation Interface
(The Eurographics Association, 2008) Liarokapis, Fotis; Katerina Mania and Eric Reinhard
This paper presents experimental results of a mobile mixed reality interface designed for geovisualization of 3D realistic urban environments which allows dynamic switching between three visualization domains: a virtual reality; an augmented reality and a mixed reality interface to get the best possible representation for visual exploration. On each domain, four different types of geovisualisation and navigation aids can be superimposed including georeferenced 3D maps, 2D digital maps, spatial 3D sound and 3D/2D textual annotations. Interaction is performed using keyboard, mouse, menus and tangible ways. To gather user requirements about urban and virtual navigation and to assess the effectiveness of mobile interface, a two-stage evaluation was performed.
Contact Skinning
(The Eurographics Association, 2008) Duriez, Christian; Courtecuisse, Hadrien; Alcalde, Juan-Pablo de la Plata; Bensoussan, Pierre-Jean; Katerina Mania and Eric Reinhard
In this paper, we propose a new approach to model interactions through a skinning method. Skinning is a frequently used technique to animate a mesh based on skeleton motion. In the case of a hand motion sequence used to manipulate and grasp virtual objects, it is essential to accurately represent the contact between the virtual objects and the animated hand. To improve the level of realism, our approach allows to accurately solve friction contact laws. In addition, contact constraints defined on the surface of the hand can be applied onto the skeleton to produce plausible motion. We illustrate our work through two examples: the real-time simulation of a grasping task and a character animation based on motion capture.
FMDistance: A Fast and Effective Distance Function for Motion Capture Data
(The Eurographics Association, 2008) Onuma, Kensuke; Faloutsos, Christos; Hodgins, Jessica K.; Katerina Mania and Eric Reinhard
Given several motion capture sequences, of similar (but not identical) length, what is a good distance function? We want to find similar sequences, to spot outliers, to create clusters, and to visualize the (large) set of motion capture sequences at our disposal. We propose a set of new features for motion capture sequences. We experiment with numerous variations (112 feature-sets in total, using variations of weights, logarithms, dimensionality reduction), and we show that the appropriate combination leads to near-perfect classification on a database of 226 actions with twelve different categories, and it enables visualization of the whole database as well as outlier detection.

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