Volume 34 (2015)

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https://diglib.eg.org/handle/10.2312/11782

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CHC+RT: Coherent Hierarchical Culling for Ray Tracing
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Mattausch, Oliver; Bittner, Jirí; Jaspe, Alberto; Gobbetti, Enrico; Wimmer, Michael; Pajarola, Renato; Olga Sorkine-Hornung and Michael Wimmer
We propose a new technique for in-core and out-of-core GPU ray tracing using a generalization of hierarchical occlusion culling in the style of the CHC++ method. Our method exploits the rasterization pipeline and hardware occlusion queries in order to create coherent batches of work for localized shader-based ray tracing kernels. By combining hierarchies in both ray space and object space, the method is able to share intermediate traversal results among multiple rays. We exploit temporal coherence among similar ray sets between frames and also within the given frame. A suitable management of the current visibility state makes it possible to benefit from occlusion culling for less coherent ray types like diffuse reflections. Since large scenes are still a challenge for modern GPU ray tracers, our method is most useful for scenes with medium to high complexity, especially since our method inherently supports ray tracing highly complex scenes that do not fit in GPU memory. For in-core scenes our method is comparable to CUDA ray tracing and performs up to 5:94 better than pure shader-based ray tracing.
Interactive Dimensioning of Parametric Models
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Kelly, Tom; Wonka, Peter; Müller, Pascal; Olga Sorkine-Hornung and Michael Wimmer
We propose a solution for the dimensioning of parametric and procedural models. Dimensioning has long been a staple of technical drawings, and we present the first solution for interactive dimensioning: a dimension line positioning system that adapts to the view direction, given behavioral properties. After proposing a set of design principles for interactive dimensioning, we describe our solution consisting of the following major components. First, we describe how an author can specify the desired interactive behavior of a dimension line. Second, we propose a novel algorithm to place dimension lines at interactive speeds. Third, we introduce multiple extensions, including chained dimension lines, controls for different parameter types (e.g. discrete choices, angles), and the use of dimension lines for interactive editing. Our results show the use of dimension lines in an interactive parametric modeling environment for architectural, botanical, and mechanical models.
IsoMatch: Creating Informative Grid Layouts
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Fried, Ohad; DiVerdi, Stephen; Halber, Maciej; Sizikova, Elena; Finkelstein, Adam; Olga Sorkine-Hornung and Michael Wimmer
Collections of objects such as images are often presented visually in a grid because it is a compact representation that lends itself well for search and exploration. Most grid layouts are sorted using very basic criteria, such as date or filename. In this work we present a method to arrange collections of objects respecting an arbitrary distance measure. Pairwise distances are preserved as much as possible, while still producing the specific target arrangement which may be a 2D grid, the surface of a sphere, a hierarchy, or any other shape. We show that our method can be used for infographics, collection exploration, summarization, data visualization, and even for solving problems such as where to seat family members at a wedding. We present a fast algorithm that can work on large collections and quantitatively evaluate how well distances are preserved.
Efficient Local Histogram Searching via Bitmap Indexing
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Wei, Tzu-Hsuan; Chen, Chun-Ming; Biswas, Ayan; H. Carr, K.-L. Ma, and G. Santucci
Representing features by local histograms is a proven technique in several volume analysis and visualization applications including feature tracking and transfer function design. The efficiency of these applications, however, is hampered by the high computational complexity of local histogram computation and matching. In this paper, we propose a novel algorithm to accelerate local histogram search by leveraging bitmap indexing. Our method avoids exhaustive searching of all voxels in the spatial domain by examining only the voxels whose values fall within the value range of user-defined local features and their neighborhood. Based on the idea that the value range of local features is in general much smaller than the dynamic range of the entire dataset, we propose a local voting scheme to construct the local histograms so that only a small number of voxels need to be examined. Experimental results show that our method can reduce much computational workload compared to the conventional approaches. To demonstrate the utility of our method, an interactive interface was developed to assist users in defining target features as local histograms and identify the locations of these features in the dataset.
VDub: Modifying Face Video of Actors for Plausible Visual Alignment to a Dubbed Audio Track
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Garrido, Pablo; Valgaerts, Levi; Sarmadi, Hamid; Steiner, Ingmar; Varanasi, Kiran; Perez, Patrick; Theobalt, Christian; Olga Sorkine-Hornung and Michael Wimmer
In many countries, foreign movies and TV productions are dubbed, i.e., the original voice of an actor is replaced with a translation that is spoken by a dubbing actor in the country's own language. Dubbing is a complex process that requires specific translations and accurately timed recitations such that the new audio at least coarsely adheres to the mouth motion in the video. However, since the sequence of phonemes and visemes in the original and the dubbing language are different, the video-to-audio match is never perfect, which is a major source of visual discomfort. In this paper, we propose a system to alter the mouth motion of an actor in a video, so that it matches the new audio track. Our paper builds on high-quality monocular capture of 3D facial performance, lighting and albedo of the dubbing and target actors, and uses audio analysis in combination with a space-time retrieval method to synthesize a new photo-realistically rendered and highly detailed 3D shape model of the mouth region to replace the target performance. We demonstrate plausible visual quality of our results compared to footage that has been professionally dubbed in the traditional way, both qualitatively and through a user study.
Efficient Variational Light Field View Synthesis For Making Stereoscopic 3D Images
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhang, Lei; Zhang, Yu-Hang; Huang, Hua; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We present a novel approach for making stereoscopic images by variational view synthesis on the multi-perspective light field. With the intended disparities as constraints, we specialize the generative variational model by incorporating per-pixel viewpoint assignment to synthesize the stereo pair. Also, we improve the variational solution by use of explicit weighted average on the light field. Our algorithm is able to handle arbitrary disparity remapping, thus enabling more flexible disparity control for the desired stereoscopic effect. The experiments demonstrate the effectiveness and efficiency for making the stereoscopic 3D images based on the light field.
Compressive Image Reconstruction in Reduced Union of Subspaces
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Miandji, Ehsan; Kronander, Joel; Unger, Jonas; Olga Sorkine-Hornung and Michael Wimmer
We present a new compressed sensing framework for reconstruction of incomplete and possibly noisy images and their higher dimensional variants, e.g. animations and light-fields. The algorithm relies on a learning-based basis representation. We train an ensemble of intrinsically two-dimensional (2D) dictionaries that operate locally on a set of 2D patches extracted from the input data. We show that one can convert the problem of 2D sparse signal recovery to an equivalent 1D form, enabling us to utilize a large family of sparse solvers. The proposed framework represents the input signals in a reduced union of subspaces model, while allowing sparsity in each subspace. Such a model leads to a much more sparse representation than widely used methods such as K-SVD. To evaluate our method, we apply it to three different scenarios where the signal dimensionality varies from 2D (images) to 3D (animations) and 4D (light-fields). We show that our method outperforms state-of-the-art algorithms in computer graphics and image processing literature.
Content-Independent Multi-Spectral Display Using Superimposed Projections
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Li, Yuqi; Majumder, Aditi; Lu, Dongming; Gopi, Meenakshisundaram; Olga Sorkine-Hornung and Michael Wimmer
Many works focus on multi-spectral capture and analysis, but multi-spectral display still remains a challenge. Most prior works on multi-primary displays use ad-hoc narrow band primaries that assure a larger color gamut, but cannot assure a good spectral reproduction. Content-dependent spectral analysis is the only way to produce good spectral reproduction, but cannot be applied to general data sets. Wide primaries are better suited for assuring good spectral reproduction due to greater coverage of the spectral range, but have not been explored much. In this paper we explore the use of wide band primaries for accurate spectral reproduction for the first time and present the first content-independent multi-spectral display achieved using superimposed projections with modified wide band primaries. We present a content-independent primary selection method that selects a small set of n primaries from a large set of m candidate primaries where m > n. Our primary selection method chooses primaries with complete coverage of the range of visible wavelength (for good spectral reproduction accuracy), low interdependency (to limit the primaries to a small number) and higher light throughput (for higher light efficiency). Once the primaries are selected, the input values of the different primary channels to generate a desired spectrum are computed using an optimization method that minimizes spectral mismatch while maximizing visual quality. We implement a real prototype of multi-spectral display consisting of 9-primaries using three modified conventional 3-primary projectors, and compare it with a conventional display to demonstrate its superior performance. Experiments show our display is capable of providing large gamut assuring a good visual appearance while displaying any multi-spectral images at a high spectral accuracy.
Multiple Facial Image Editing Using Edge-Aware PDE Learning
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Liang, Lingyu; Jin, Lianwen; Zhang, Xin; Xu, Yong; Stam, Jos and Mitra, Niloy J. and Xu, Kun
This paper introduces a novel facial editing tool, called edge-aware mask, to achieve multiple photo-realistic rendering effects in a unified framework. The edge-aware masks facilitate three basic operations for adaptive facial editing, including region selection, edit setting and region blending. Inspired by the state-of-the-art edit propagation and partial differential equation (PDE) learning method, we propose an adaptive PDE model with facial priors for masks generation through edge-aware diffusion. The edge-aware masks can automatically fit the complex region boundary with great accuracy and produce smooth transition between different regions, which significantly improves the visual consistence of face editing and reduce the human intervention. Then, a unified and flexible facial editing framework is constructed, which consists of layer decomposition, edge-aware masks generation, and layer/mask composition. The combinations of multiple facial layers and edge-aware masks can achieve various facial effects simultaneously, including face enhancement, relighting, makeup and face blending etc. Qualitative and quantitative evaluations were performed using different datasets for different facial editing tasks. Experiments demonstrate the effectiveness and flexibility of our methods, and the comparisons with the previous methods indicate that improved results are obtained using the combination of multiple edge-aware masks.
Visual Assessment of Alleged Plagiarism Cases
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Riehmann, Patrick; Potthast, Martin; Stein, Benno; Froehlich, Bernd; H. Carr, K.-L. Ma, and G. Santucci
We developed a visual analysis tool to support the verification, assessment, and presentation of alleged cases of plagiarism. The analysis of a suspicious document typically results in a compilation of categorized ''finding spots''. The categorization reveals the way in which the suspicious text fragment was created from the source, e.g. by obfuscation, translation, or by shake and paste. We provide a three-level approach for exploring the finding spots in context. The overview shows the relationship of the entire suspicious document to the set of source documents. A glyph-based view reveals the structural and textual differences and similarities of a set of finding spots and their corresponding source text fragments. For further analysis and editing of the finding spot's assessment, the actual text fragments can be embedded side-by-side in the diffline view. The different views are tied together by versatile navigation and selection operations. Our expert reviewers confirm that our tool provides a significant improvement over existing static visualizations for assessing plagiarism cases.
Scalable Partitioning for Parallel Position Based Dynamics
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Fratarcangeli, Marco; Pellacini, Fabio; Olga Sorkine-Hornung and Michael Wimmer
We introduce a practical partitioning technique designed for parallelizing Position Based Dynamics, and exploiting the ubiquitous multi-core processors present in current commodity GPUs. The input is a set of particles whose dynamics is influenced by spatial constraints. In the initialization phase, we build a graph in which each node corresponds to a constraint and two constraints are connected by an edge if they influence at least one common particle. We introduce a novel greedy algorithm for inserting additional constraints (phantoms) in the graph such that the resulting topology is ˆ q-colourable, where ˆ q 2 is an arbitrary number. We color the graph, and the constraints with the same color are assigned to the same partition. Then, the set of constraints belonging to each partition is solved in parallel during the animation phase. We demonstrate this by using our partitioning technique; the performance hit caused by the GPU kernel calls is significantly decreased, leaving unaffected the visual quality, robustness and speed of serial position based dynamics.
Geometrically Exact Simulation of Inextensible Ribbon
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Shen, Zhongwei; Huang, Jin; Chen, Wei; Bao, Hujun; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Narrow, inextensible, and naturally flat ribbons have some special and interesting phenomena under isometric deformations. Although a ribbon has a shape between rod and shell, directly applying the geometric representation designed for them imposes a challenge to faithfully reproduce interesting behaviors. We thus parameterize the ribbon surface as a developable ruled surface along its centerline and represent it using a framed centerline curve. Then the elastic and kinetic energy of the ribbon surface can be equivalently yet compactly described by the framed centerline curve only. To avoid numerical singularity when developability is violated, a finite Taylor series approximation to the potential energy is adopted. Under the observation that the off-centerline part of ribbon contributes little dynamic effect, the kinetic energy is simplified with respect to the centerline velocity only. For efficiency, each time step is separated into two stages: dynamically evolving the centerline, and then quasi-statically updating the ruling. We validate the method with qualitative analysis and ribbon specific phenomena comparisons with real-world scenarios. A set of comparisons to rod and shell model is also provided to demonstrate the advantages of our method.
Finite-Time Mass Separation for Comparative Visualizations of Inertial Particles
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Günther, Tobias; Theisel, Holger; H. Carr, K.-L. Ma, and G. Santucci
The visual analysis of flows with inertial particle trajectories is a challenging problem because time-dependent particle trajectories additionally depend on mass, which gives rise to an infinite number of possible trajectories passing through every point in space-time. This paper presents an approach to a comparative visualization of the inertial particles' separation behavior. For this, we define the Finite-Time Mass Separation (FTMS), a scalar field that measures at each point in the domain how quickly inertial particles separate that were released from the same location but with slightly different mass. Extracting and visualizing the mass that induces the largest separation provides a simplified view on the critical masses. By using complementary coordinated views, we additionally visualize corresponding inertial particle trajectories in space-time by integral curves and surfaces. For a quantitative analysis, we plot Euclidean and arc length-based distances to a reference particle over time, which allows to observe the temporal evolution of separation events. We demonstrate our approach on a number of analytic and one real-world unsteady 2D field.
Biologically-Inspired Visual Simulation of Insect Swarms
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Li, Weizi; Wolinski, David; Pettré, Julien; Lin, Ming C.; Olga Sorkine-Hornung and Michael Wimmer
Representing the majority of living animals, insects are the most ubiquitous biological organisms on Earth. Being able to simulate insect swarms could enhance visual realism of various graphical applications. However, the very complex nature of insect behaviors makes its simulation a challenging computational problem. To address this, we present a general biologically-inspired framework for visual simulation of insect swarms. Our approach is inspired by the observation that insects exhibit emergent behaviors at various scales in nature. At the low level, our framework automatically selects and configures the most suitable steering algorithm for the local collision avoidance task. At the intermediate level, it processes insect trajectories into piecewise-linear segments and constructs probability distribution functions for sampling waypoints. These waypoints are then evaluated by the Metropolis- Hastings algorithm to preserve global structures of insect swarms at the high level. With this biologically inspired, data-driven approach, we are able to simulate insect behaviors at different scales and we evaluate our simulation using both qualitative and quantitative metrics. Furthermore, as insect data could be difficult to acquire, our framework can be adopted as a computer-assisted animation tool to interpret sketch-like input as user control and generate simulations of complex insect swarming phenomena.
Adaptive Recommendations for Enhanced Non-linear Exploration of Annotated 3D Objects
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Rodriguez, Marcos Balsa; Agus, Marco; Marton, Fabio; Gobbetti, Enrico; H. Carr, K.-L. Ma, and G. Santucci
We introduce a novel approach for letting casual viewers explore detailed 3D models integrated with structured spatially associated descriptive information organized in a graph. Each node associates a subset of the 3D surface seen from a particular viewpoint to the related descriptive annotation, together with its author-defined importance. Graph edges describe, instead, the strength of the dependency relation between information nodes, allowing content authors to describe the preferred order of presentation of information. At run-time, users navigate inside the 3D scene using a camera controller, while adaptively receiving unobtrusive guidance towards interesting viewpoints and history- and location-dependent suggestions on important information, which is adaptively presented using 2D overlays displayed over the 3D scene. The capabilities of our approach are demonstrated in a real-world cultural heritage application involving the public presentation of sculptural complex on a large projection-based display. A user study has been performed in order to validate our approach.
3D Fabrication of 2D Mechanisms
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Hergel, Jean; Lefebvre, Sylvain; Olga Sorkine-Hornung and Michael Wimmer
The success of physics sandbox applications and physics-based puzzle games is a strong indication that casual users and hobbyists enjoy designing mechanisms, for educational or entertainment purposes. In these applications, a variety of mechanisms are designed by assembling two-dimensional shapes, creating gears, cranks, cams, and racks. The experience is made enjoyable by the fact that the user does not need to worry about the intricate geometric details that would be necessary to produce a real mechanism. In this paper, we propose to start from such casual designs of mechanisms and turn them into a 3D model that can be printed onto widely available, inexpensive filament based 3D printers. Our intent is to empower the users of such tools with the ability to physically realize their mechanisms and see them operate in the real world. To achieve this goal we tackle several challenges. The input 2D mechanism allows for some parts to overlap during simulation. These overlapping parts have to be resolved into non-intersecting 3D parts in the real mechanism. We introduce a novel scheme based on the idea of including moving parts into one another whenever possible. This reduces bending stresses on axles compared to previous methods. Our approach supports sliding parts and arbitrarily shaped mechanical parts in the 2D input. The exact 3D shape of the parts is inferred from the 2D input and the simulation of the mechanism, using boolean operations between shapes. The input mechanism is often simply attached to the background. We automatically synthesize a chassis by formulating a topology optimization problem, taking into account the stresses exerted by the mechanism on the chassis through time.
A One-dimensional Homologically Persistent Skeleton of an Unstructured Point Cloud in any Metric Space
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Kurlin, Vitaliy; Mirela Ben-Chen and Ligang Liu
Real data are often given as a noisy unstructured point cloud, which is hard to visualize. The important problem is to represent topological structures hidden in a cloud by using skeletons with cycles. All past skeletonization methods require extra parameters such as a scale or a noise bound. We define a homologically persistent skeleton, which depends only on a cloud of points and contains optimal subgraphs representing 1-dimensional cycles in the cloud across all scales. The full skeleton is a universal structure encoding topological persistence of cycles directly on the cloud. Hence a 1-dimensional shape of a cloud can be now easily predicted by visualizing our skeleton instead of guessing a scale for the original unstructured cloud. We derive more subgraphs to reconstruct provably close approximations to an unknown graph given only by a noisy sample in any metric space. For a cloud of n points in the plane, the full skeleton and all its important subgraphs can be computed in time O(n log n).
Filtered Stochastic Shadow Mapping Using a Layered Approach
(Copyright © 2015 The Eurographics Association and John Wiley & Sons Ltd., 2015) Andersson, M.; Hasselgren, J.; Munkberg, J.; Akenine‐Möller, T.; Deussen, Oliver and Zhang, Hao (Richard)
Given a stochastic shadow map rendered with motion blur, our goal is to render an image from the eye with motion‐blurred shadows with as little noise as possible. We use a layered approach in the shadow map and reproject samples along the average motion vector, and then perform lookups in this representation. Our results include substantially improved shadow quality compared to previous work and a fast graphics processing unit (GPU) implementation. In addition, we devise a set of scenes that are designed to bring out and show problematic cases for motion‐blurred shadows. These scenes have difficult occlusion characteristics, and may be used in future research on this topic.An octopus in motion casting a complex motion‐blurred shadow rendered by our algorithm. With the same input samples, our algorithm has significantly less noise compared to time‐dependent shadow maps (TSM). At equal time, the noise level is still largely reduced. The animated octopus mesh is taken from the Alembic source distribution.

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