29-Issue 8

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https://diglib.eg.org/handle/10.2312/159

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Transparent and Specular Object Reconstruction
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Ihrke, Ivo; Kutulakos, Kiriakos N.; Lensch, Hendrik P. A.; Magnor, Marcus; Heidrich, Wolfgang
This state of the art report covers reconstruction methods for transparent and specular objects or phenomena. While the 3D acquisition of opaque surfaces with Lambertian reflectance is a well-studied problem, transparent, refractive, specular and potentially dynamic scenes pose challenging problems for acquisition systems. This report reviews and categorizes the literature in this field.Despite tremendous interest in object digitization, the acquisition of digital models of transparent or specular objects is far from being a solved problem. On the other hand, real-world data is in high demand for applications such as object modelling, preservation of historic artefacts and as input to data-driven modelling techniques. With this report we aim at providing a reference for and an introduction to the field of transparent and specular object reconstruction.We describe acquisition approaches for different classes of objects. Transparent objects/phenomena that do not change the straight ray geometry can be found foremost in natural phenomena. Refraction effects are usually small and can be considered negligible for these objects. Phenomena as diverse as fire, smoke, and interstellar nebulae can be modelled using a straight ray model of image formation. Refractive and specular surfaces on the other hand change the straight rays into usually piecewise linear ray paths, adding additional complexity to the reconstruction problem. Translucent objects exhibit significant sub-surface scattering effects rendering traditional acquisition approaches unstable. Different classes of techniques have been developed to deal with these problems and good reconstruction results can be achieved with current state-of-the-art techniques. However, the approaches are still specialized and targeted at very specific object classes. We classify the existing literature and hope to provide an entry point to this exiting field.
Creating and Animating Subject-Specific Anatomical Models
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Gilles, B.; Reveret, L.; Pai, D. K.
Creating and animating subject-specific anatomical models is traditionally a difficult process involving medical image segmentation, geometric corrections and the manual definition of kinematic parameters. In this paper, we introduce a novel template morphing algorithm that facilitates three-dimensional modelling and parameterization of skeletons. Target data can be either medical images or surfaces of the whole skeleton. We incorporate prior knowledge about bone shape, the feasible skeleton pose and the morphological variability in the population. This allows for noise reduction, bone separation and the transfer, from the template, of anatomical and kinematical information not present in the input data. Our approach treats both local and global deformations in successive regularization steps: smooth elastic deformations are represented by an as-rigid-as-possible displacement field between the reference and current configuration of the template, whereas global and discontinuous displacements are estimated through a projection onto a statistical shape model and a new joint pose optimization scheme with joint limits.
Reviewers
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
Tone Mapping Operators on Small Screen Devices: An Evaluation Study
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Urbano, C.; Magalhaes, L.; Moura, J.; Bessa, M.; Marcos, A.; Chalmers, A.
In the last decade, an increasing number of techniques have been developed to reproduce high dynamic range imagery on traditional displays. These techniques, known as Tone Mapping Operators (TMOs), have been compared and ranked in different ways according to several image characteristics. However, none of these algorithms has been developed specifically for small screen devices (SSD). In this paper, we present an evaluation of currently used TMOs to show that SSDs with limited size, resolution and colour depth require specific research to find or create an appropriate solution. The research described in this paper is based on psychophysical experiments; using three different types of displays (CRT, LCD and SSD). The obtained results show that rankings obtained are similar for the LCD and CRT but are significantly different for the SSD. Furthermore, these rankings show additionally that some characteristics of TMOs need to be emphasized to obtain better high-fidelity mapped images for SSDs.
Fullsphere Irradiance Factorization for Real-Time All-Frequency Illumination for Dynamic Scenes
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Michael, D.; Chrysanthou, Y.
Computation of illumination with soft-shadows from all-frequency environment maps, is a computationally expensive process. Use of pre-computation add the limitation that receiver s geometry must be known in advance, since Irradiance computation takes into account the receiver s normal direction. We propose a method that using a new notion that we introduce, the Fullsphere Irradiance, allows us to accumulate the contribution from all light sources in the scene, on a possible receiver without knowing the receiver s geometry. This expensive computation is done in a pre-processing step. The pre-computed value is used at run time to compute the Irradiance arriving at any receiver with known direction. We show how using this technique we compute soft-shadows and self-shadows in real-time from all-frequency environments, with only modest memory requirements. A GPU implementation of the method, yields high frame rates even for complex scenes with dozens of dynamic occluders and receivers.
A Key-Pose Caching System for Rendering an Animated Crowd in Real-Time
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lister, W.; Laycock, R.G.; Day, A.M.
We present a method to accelerate the visualization of large crowds of animated characters. Linear-blend skinning remains the dominant approach for animating a crowd but its efficiency can be improved by utilizing the temporal and intra-crowd coherencies that are inherent within a populated scene. Our work adopts a caching system that enables a skinned key-pose to be re-used by multi-pass rendering, between multiple agents and across multiple frames. We investigate two different methods; an intermittent caching scheme (whereby each member of a crowd is animated using only its nearest key-pose) and an interpolative approach that enables key-pose blending to be supported. For the latter case, we show that finding the optimal set of key-poses to store is an NP-hard problem and present a greedy algorithm suitable for real-time applications. Both variants deliver a worthwhile performance improvement in comparison to using linear-blend skinning alone.
Real Time Animation of Virtual Humans: A Trade-off Between Naturalness and Control
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Van Welbergen, H.; Van Basten, B. J. H.; Egges, A.; Ruttkay, Zs. M.; Overmars, M. H.
Virtual humans are employed in many interactive applications using 3D virtual environments, including (serious) games. The motion of such virtual humans should look realistic (or natural and allow interaction with the surroundings and other (virtual) humans. Current animation techniques differ in the trade-off they offer between motion naturalness and the control that can be exerted over the motion. We show mechanisms to parametrize, combine (on different body parts) and concatenate motions generated by different animation techniques. We discuss several aspects of motion naturalness and show how it can be evaluated. We conclude by showing the promise of combinations of different animation paradigms to enhance both naturalness and control.
A Smoke Visualization Model for Capturing Surface-Like Features
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Park, Jinho; Seol, Yeongho; Cordier, Frederic; Noh, Junyong
Incense, candle smoke and cigarette smoke often exhibit smoke flows with a surface-like appearance. Although delving into well-known computational fluid dynamics may provide a solution to create such an appearance, we propose a much efficient alternative that combines a low-resolution fluid simulation with explicit geometry provided by NURBS surfaces. Among a wide spectrum of fluid simulation, our algorithm specifically tailors to reproduce the semi-transparent surface look and motion of the smoke. The main idea is that we follow the traces called streaklines created by the advected particles from a simulation and reconstruct NURBS surfaces passing through them. Then, we render the surfaces by applying an opacity map to each surface, where the opacity map is created by utilizing the smoke density and the characteristics of the surface contour. Augmenting the results from low-resolution simulations such a way requires a low computational cost and memory usage by design.
Electrostatic Halftoning
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Schmaltz, Christian; Gwosdek, Pascal; Bruhn, Andres; Weickert, Joachim
We introduce a new global approach for image dithering, stippling, screening and sampling. It is inspired by the physical principles of electrostatics. Repelling forces between equally charged particles create a homogeneous distribution in flat areas, while attracting forces from the image brightness values ensure a high approximation quality. Our model is transparent and uses only two intuitive parameters: One steers the granularity of our halftoning approach, and the other its regularity. We evaluate two versions of our algorithm: A discrete version for dithering that ties points to grid positions, as well as a continuous one which does not have this restriction, and can thus be used for stippling or sampling density functions. Our methods create very few visual artefacts, reveal favourable blue-noise behaviour in the frequency domain, and have a lower approximation error under Gaussian convolution than state-of-the-art methods.
How to Write a Visualization Research Paper: A Starting Point
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Laramee, Robert S.
This paper attempts to explain the mechanics of writing a research paper in visualization. This serves as a useful starting point for those who have never written a research paper before or have very little previous experience. After all, no one is born knowing how to write one. And yet, there are certain elements, a commonality, that should be found in virtually all good visualization research papers. We give our recommendations as to each section a good research paper consists of as well as what each section contains. This paper itself follows our recommended structure.We believe that paper writing should start with the abstract. The abstract can be approximately 6-12 sentences. It is a difficult starting point, but it forces the author to write down a concise description of what they are researching and what the benefits are. Chances are, if the author cannot start out by writing an abstract, then it is not clear in the author s mind what the paper should be about. Of course, the abstract will be refined and updated during the paper writing process. The abstract should concisely (1) identify the research topic, (2) describe the novelty of the presented work and (3) identify the benefits and advantages that result.
Teaching Quaternions is not Complex
(The Eurographics Association and Blackwell Publishing Ltd, 2010) McDonald, J.
Quaternions are used in many fields of science and computing, but teaching them remains challenging. Students can have a great deal of trouble understanding essentially what quaternions are and how they can represent rotation matrices. In particular, the similarity transform, which actually achieves rotation, can often be baffling even after students have seen a full derivation. This paper outlines a constructive method for teaching quaternions, which allows students to build intuition about what quaternions are, and why simple multiplication is not adequate to represent a rotation. Through a set of examples, it demonstrates exactly how quaternions relate to rotation matrices, what goes wrong when qv is naively used to rotate vectors, and how the similarity transform fixes the problem.
31st EUROGRAPHICS General Assembly
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
A Shape Descriptor for 3D Objects Based on Rotational Symmetry
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Martinek, M.; Grosso, R.; Greiner, G.
The ability to extract spatial features from 3D objects is essential for applications such as shape matching and object classification. However, designing an effective feature vector which is invariant with respect to rotation, translation and scaling is a challenging task and is often solved by normalization techniques such as PCA, which can give rise to poor object alignment. In this paper, we introduce a novel method to extract robust and invariant 3D features based on rotational symmetry. By applying a rotation-variant similarity function on two instances of the same 3D object, we can define an autocorrelation on the object in the space of rotations. We use a special representation of the SO(3) and determine significant rotation axes for an object by means of optimization techniques. By sampling the similarity function via rotations around these axes, we obtain robust and invariant features, which are descriptive for the underlying geometry. The resulting feature vector cannot only be used to characterize an object with respect to rotational symmetry but also to define a distance between 3D models. Because the features are compact and pre-computable, our method is suitable to perform similarity searches in large 3D databases.
High-Quality Screen-Space Ambient Occlusion using Temporal Coherence
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Mattausch, Oliver; Scherzer, Daniel; Wimmer, Michael
Ambient occlusion is a cheap but effective approximation of global illumination. Recently, screen-space ambient occlusion (SSAO) methods, which sample the frame buffer as a discretization of the scene geometry, have become very popular for real-time rendering. We present temporal SSAO (TSSAO), a new algorithm which exploits temporal coherence to produce high-quality ambient occlusion in real time. Compared to conventional SSAO, our method reduces both noise as well as blurring artefacts due to strong spatial filtering, faithfully representing fine-grained geometric structures. Our algorithm caches and reuses previously computed SSAO samples, and adaptively applies more samples and spatial filtering only in regions that do not yet have enough information available from previous frames. The method works well for both static and dynamic scenes.
Table of Contents and Cover
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
REPORT OF THE STATUTORY AUDITORS TO THE GENERAL MEETING OF THE MEMBERS OF EUROGRAPHICS ASSOCIATION GENEVA
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
An Eyeglass Simulator Using Conoid Tracing
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Kakimoto, M.; Tatsukawa, T.; Nishita, T.
This paper proposes a method for displaying images at the fovea of the retina taking visual acuity into account. Previous research has shown that a point light source projected onto the retina forms an ellipse, which can be computed with wavefront tracing from each point in space. We propose a novel concept using conoid tracing, with which we can acquire defocusing information several times faster than that acquired by previous methods. We also show that conoid tracing is more robust and produces higher quality results. In conoid tracing the ray is regarded as a conoid, a thin cone-like shape with varying elliptical cross-section. The viewing ray from the retina is traced as a conoid and evaluated at each sample location. Using the sampled and pre-computed data for the spatial distribution of blurring, we implemented an interactive eyeglass simulator. This paper demonstrates some visualization results utilizing the interactivity of the simulator, which an eyeglass lens design company uses to evaluate the design of complex progressive lenses.
Generalized Use of Non-Terminal Symbols for Procedural Modeling
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Krecklau, L.; Pavic, D.; Kobbelt, L.
We present the new procedural modeling language, (Generalized Grammar), which adapts various concepts from general purpose programming languages to provide high descriptive power with well-defined semantics and a simple syntax which is easily readable even by non-programmers. The term Generalized reflects two kinds of generalization. On the one hand, we extend the scope of previous architectural modeling languages by allowing for multiple types of non-terminal objects with domain-specific operators and attributes. On the other hand, the language accepts non-terminal symbols as parameters in modeling rules and thus enables the definition of abstract structure templates for flexible re-use within the grammar. By deriving, from the well-established programming language Python, we can make sure that our modeling language has a well-defined semantics. For illustration, we apply, to architectural as well as plant modeling to demonstrate its descriptive power with some complex examples.
Generating Classic Mosaics with Graph Cuts
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Liu, Y.; Veksler, O.; Juan, O.
Classic mosaic is an old and durable art form. Generating artificial classic mosaics from digital images is an interesting problem that has attracted attention in recent years. Previous approaches to mosaic generation are largely based on heuristics, and therefore it is harder to analyse, predict and improve their performance. In addition, previous methods have a number of disadvantages, such as requiring that the number of tiles in a mosaic is known a priori, or relying on extensive user interaction, or using heuristics for tile placement that lead to visible artefacts. We propose a classic mosaic generation algorithm that is based on a principled global optimization. Our approach is fully automatic. We design and optimize an objective function that incorporates the desired mosaic properties, such as tile alignment to significant image edges, prohibiting tile overlap, etc. Our optimization method is based on graph cuts, which proved to be a powerful optimization tool in graphics and computer vision. Experimental comparison to previous work demonstrate the advantages of our approach.
Chain Shape Matching for Simulating Complex Hairstyles
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Rungjiratananon, W.; Kanamori, Y.; Nishita, T.
Animations of hair dynamics greatly enrich the visual attractiveness of human characters. Traditional simulation techniques handle hair as clumps or continuum for efficiency; however, the visual quality is limited because they cannot represent the fine-scale motion of individual hair strands. Although a recent mass-spring approach tackled the problem of simulating the dynamics of every strand of hair, it required a complicated setting of springs and suffered from high computational cost. In this paper, we base the animation of hair on such a fine-scale on Lattice Shape Matching (LSM), which has been successfully used for simulating deformable objects. Our method regards each strand of hair as a chain of particles, and computes geometrically derived forces for the chain based on shape matching. Each chain of particles is simulated as an individual strand of hair. Our method can easily handle complex hairstyles such as curly or afro styles in a numerically stable way. While our method is not physically based, our GPU-based simulator achieves visually plausible animations consisting of several tens of thousands of hair strands at interactive rates.

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