EG 2015 - Full Papers - CGF 34-Issue 2

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EUROGRAPHICS 2015: CGF 34-2 Frontmatter

Olga Sorkine-Hornung
Michael Wimmer
Images & Scenes

Hallucinating Stereoscopy from a Single Image

Zeng, Qiong
Chen, Wenzheng
Wang, Huan
Tu, Changhe
Cohen-Or, Daniel
Lischinski, Dani
Chen, Baoquan
Images & Scenes

Composition-Aware Scene Optimization for Product Images

Liu, Tianqiang
McCann, Jim
Li, Wilmot
Funkhouser, Thomas
Sampling & Skins

Sample Elimination for Generating Poisson Disk Sample Sets

Yuksel, Cem
Sampling & Skins

Compressive Image Reconstruction in Reduced Union of Subspaces

Miandji, Ehsan
Kronander, Joel
Unger, Jonas
Sampling & Skins

A Biophysically-Based Model of the Optical Properties of Skin Aging

Iglesias-Guitian, Jose A.
Aliaga, Carlos
Jarabo, Adrian
Gutierrez, Diego
Image and Video Processing

Panoramic Video from Unstructured Camera Arrays

Perazzi, Federico
Sorkine-Hornung, Alexander
Zimmer, Henning
Kaufmann, Peter
Wang, Oliver
Watson, Scott
Gross, Markus
Image and Video Processing

High-Order Recursive Filtering of Non-Uniformly Sampled Signals for Image and Video Processing

Gastal, Eduardo S. L.
Oliveira, Manuel M.
Image and Video Processing

Designing Camera Networks by Convex Quadratic Programming

Ghanem, Bernard
Cao, Yuanhao
Wonka, Peter
Image and Video Processing

Jointly Optimized Regressors for Image Super-resolution

Dai, Dengxin
Timofte, Radu
Gool, Luc Van
Procedural and Parametric Modeling

Parallel, Realistic and Controllable Terrain Synthesis

Gain, James
Merry, Bruce
Marais, Patrick
Procedural and Parametric Modeling

Interactive Dimensioning of Parametric Models

Kelly, Tom
Wonka, Peter
Müller, Pascal
Image Collections

Distilled Collections from Textual Image Queries

Averbuch-Elor, Hadar
Wan, Yunhai
Qian, Yiming
Gong, Minglun
Kopf, Johannes
Zhang, Hao
Cohen-Or, Daniel
Image Collections

Guiding Image Manipulations using Shape-appearance Subspaces from Co-alignment of Image Collections

Nguyen, Chuong H.
Nalbach, Oliver
Ritschel, Tobias
Seidel, Hans-Peter
Image Collections

IsoMatch: Creating Informative Grid Layouts

Fried, Ohad
DiVerdi, Stephen
Halber, Maciej
Sizikova, Elena
Finkelstein, Adam
Image Collections

Comprehensible Video Thumbnails

Kim, Jongdae
Gray, Charles
Asente, Paul
Collomosse, John
All About Faces

Interactive Generation of Realistic Facial Wrinkles from Sketchy Drawings

Kim, Hyeon-Joong
Öztireli, A. Cengiz
Shin, Il-Kyu
Gross, Markus
Choi, Soo-Mi
All About Faces

VDub: Modifying Face Video of Actors for Plausible Visual Alignment to a Dubbed Audio Track

Garrido, Pablo
Valgaerts, Levi
Sarmadi, Hamid
Steiner, Ingmar
Varanasi, Kiran
Perez, Patrick
Theobalt, Christian
Cities & Roads

Layer-Based Procedural Design of Façades

Ilcík, Martin
Musialski, Przemyslaw
Auzinger, Thomas
Wimmer, Michael
Cities & Roads

Template Assembly for Detailed Urban Reconstruction

Nan, Liangliang
Jiang, Caigui
Ghanem, Bernard
Wonka, Peter
Fabrication

3D Fabrication of 2D Mechanisms

Hergel, Jean
Lefebvre, Sylvain
Fabrication

Approximating Free-form Geometry with Height Fields for Manufacturing

Herholz, Philipp
Matusik, Wojciech
Alexa, Marc
Fabrication

High Reliefs from 3D Scenes

Arpa, Sami
Süsstrunk, Sabine
Hersch, Roger D.
Shape Manipulation

Shape-from-Operator: Recovering Shapes from Intrinsic Operators

Boscaini, Davide
Eynard, Davide
Kourounis, Drosos
Bronstein, Michael M.
Shape Manipulation

Skeleton-Intrinsic Symmetrization of Shapes

Zheng, Qian
Hao, Zhuming
Huang, Hui
Xu, Kai
Zhang, Hao
Cohen-Or, Daniel
Chen, Baoquan
Shape Manipulation

Interactive Disassembly Planning for Complex Objects

Kerbl, Bernhard
Kalkofen, Denis
Steinberger, Markus
Schmalstieg, Dieter
Shape Manipulation

Approximating the Generalized Voronoi Diagram of Closely Spaced Objects

Edwards, John
Daniel, Eric
Pascucci, Valerio
Bajaj, Chandrajit
Agile Hardware

Hardware-Based Non-Photorealistic Rendering Using a Painting Robot

Lindemeier, Thomas
Metzner, Jens
Pollak, Lena
Deussen, Oliver
Agile Hardware

Light Chisel: 6DOF Pen Tracking

Bubník, Vojtech
Havran, Vlastimil
Agile Hardware

Content-Independent Multi-Spectral Display Using Superimposed Projections

Li, Yuqi
Majumder, Aditi
Lu, Dongming
Gopi, Meenakshisundaram
Colors and Textures

Self Tuning Texture Optimization

Kaspar, Alexandre
Neubert, Boris
Lischinski, Dani
Pauly, Mark
Kopf, Johannes
Colors and Textures

Woodification: User-Controlled Cambial Growth Modeling

Kratt, Julian
Spicker, Marc
Guayaquil, Alejandro
Fiser, Marek
Pirk, Sören
Deussen, Oliver
Hart, John C.
Benes, Bedrich
Colors and Textures

Color Sequence Preserving Decolorization

Yoo, Min-Joon
Lee, In-Kwon
Lee, Seungyong
Bodies in Motion

Real-Time Subspace Integration for Example-Based Elastic Material

Zhang, Wenjing
Zheng, Jianmin
Thalmann, Nadia Magnenat
Colors and Textures

Paint and Click: Unified Interactions for Image Boundaries

Summa, Brian
Gooch, Amy A.
Scorzelli, Giorgio
Pascucci, Valerio
Bodies in Motion

Scalable Partitioning for Parallel Position Based Dynamics

Fratarcangeli, Marco
Pellacini, Fabio
Bodies in Motion

Improving Sampling-based Motion Control

Liu, Libin
Yin, KangKang
Guo, Baining
Bodies in Motion

Biologically-Inspired Visual Simulation of Insect Swarms

Li, Weizi
Wolinski, David
Pettré, Julien
Lin, Ming C.
Reconstruction

Database-Assisted Object Retrieval for Real-Time 3D Reconstruction

Li, Yangyan
Dai, Angela
Guibas, Leonidas
Nießner, Matthias
Reconstruction

SmartAnnotator: An Interactive Tool for Annotating Indoor RGBD Images

Wong, Yu-Shiang
Chu, Hung-Kuo
Mitra, Niloy J.
Reconstruction

Adaptable Anatomical Models for Realistic Bone Motion Reconstruction

Zhu, Lifeng
Hu, Xiaoyan
Kavan, Ladislav
Fluids & Flows

A Dimension-reduced Pressure Solver for Liquid Simulations

Ando, Ryoichi
Thürey, Nils
Wojtan, Chris
Fluids & Flows

A Cut-Cell Geometric Multigrid Poisson Solver for Fluid Simulation

Weber, Daniel
Mueller-Roemer, Johannes
Stork, André
Fellner, Dieter W.
Fluids & Flows

Implicit Formulation for SPH-based Viscous Fluids

Takahashi, Tetsuya
Dobashi, Yoshinori
Fujishiro, Issei
Nishita, Tomoyuki
Lin, Ming C.
Shape Collections

Replaceable Substructures for Efficient Part-Based Modeling

Liu, Han
Vimont, Ulysse
Wand, Michael
Cani, Marie-Paule
Hahmann, Stefanie
Rohmer, Damien
Mitra, Niloy J.
Shape Collections

Generating Design Suggestions under Tight Constraints with Gradient-based Probabilistic Programming

Ritchie, Daniel
Lin, Sharon
Goodman, Noah D.
Hanrahan, Pat
Real-Time Rendering & Quantization

T-SAH: Animation Optimized Bounding Volume Hierarchies

Bittner, Jirí
Meister, Daniel
Real-Time Rendering & Quantization

CHC+RT: Coherent Hierarchical Culling for Ray Tracing

Mattausch, Oliver
Bittner, Jirí
Jaspe, Alberto
Gobbetti, Enrico
Wimmer, Michael
Pajarola, Renato
Real-Time Rendering & Quantization

Partitioned Shadow Volumes

Gerhards, Julien
Mora, Frédéric
Aveneau, Lilian
Ghazanfarpour, Djamchid
Global Illumination

IlluminationCut

Bus, Norbert
Mustafa, Nabil H.
Biri, Venceslas
Global Illumination

Rich-VPLs for Improving the Versatility of Many-Light Methods

Simon, Florian
Hanika, Johannes
Dachsbacher, Carsten
Global Illumination

Robust Statistical Pixel Estimation

Jung, Jin Woo
Meyer, Gary
DeLong, Ralph
Global Illumination

General and Robust Error Estimation and Reconstruction for Monte Carlo Rendering

Bauszat, Pablo
Eisemann, Martin
Eisemann, Elmar
Magnor, Marcus
Splines & Meshes

Selective Degree Elevation for Multi-Sided Bézier Patches

Smith, Jason
Schaefer, Scott
Splines & Meshes

Statics Aware Grid Shells

Pietroni, Nico
Tonelli, Davide
Puppo, Enrico
Froli, Maurizio
Scopigno, Roberto
Cignoni, Paolo
Splines & Meshes

Optimal Spline Approximation via l0-Minimization

Brandt, Christopher
Seidel, Hans-Peter
Hildebrandt, Klaus


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Recent Submissions

Now showing 1 - 56 of 56
  • Item
    Hallucinating Stereoscopy from a Single Image
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Zeng, Qiong; Chen, Wenzheng; Wang, Huan; Tu, Changhe; Cohen-Or, Daniel; Lischinski, Dani; Chen, Baoquan; Olga Sorkine-Hornung and Michael Wimmer
    We introduce a novel method for enabling stereoscopic viewing of a scene from a single pre-segmented image. Rather than attempting full 3D reconstruction or accurate depth map recovery, we hallucinate a rough approximation of the scene's 3D model using a number of simple depth and occlusion cues and shape priors. We begin by depth-sorting the segments, each of which is assumed to represent a separate object in the scene, resulting in a collection of depth layers. The shapes and textures of the partially occluded segments are then completed using symmetry and convexity priors. Next, each completed segment is converted to a union of generalized cylinders yielding a rough 3D model for each object. Finally, the object depths are refined using an iterative ground fitting process. The hallucinated 3D model of the scene may then be used to generate a stereoscopic image pair, or to produce images from novel viewpoints within a small neighborhood of the original view. Despite the simplicity of our approach, we show that it compares favorably with state-of-the-art depth ordering methods. A user study was conducted showing that our method produces more convincing stereoscopic images than existing semi-interactive and automatic single image depth recovery methods.
  • Item
    Composition-Aware Scene Optimization for Product Images
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Liu, Tianqiang; McCann, Jim; Li, Wilmot; Funkhouser, Thomas; Olga Sorkine-Hornung and Michael Wimmer
    Increasingly, companies are creating product advertisements and catalog images using computer renderings of 3D scenes. A common goal for these companies is to create aesthetically appealing compositions that highlight objects of interest within the context of a scene. Unfortunately, this goal is challenging, not only due to the need to balance the trade-off among aesthetic principles and design constraints, but also because of the huge search space induced by possible camera parameters, object placement, material choices, etc. Previous methods have investigated only optimization of camera parameters. In this paper, we develop a tool that starts from an initial scene description and a set of high-level constraints provided by a stylist and then automatically generates an optimized scene whose 2D composition is improved. It does so by locally adjusting the 3D object transformations, surface materials, and camera parameters. The value of this tool is demonstrated in a variety of applications motivated by product catalogs, including rough layout refinement, detail image creation, home planning, cultural customization, and text inlay placement. Results of a perceptual study indicate that our system produces images preferable for product advertisement compared to a more traditional camera-only optimization.
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    Sample Elimination for Generating Poisson Disk Sample Sets
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Yuksel, Cem; Olga Sorkine-Hornung and Michael Wimmer
    In this paper we describe sample elimination for generating Poisson disk sample sets with a desired size. We introduce a greedy sample elimination algorithm that assigns a weight to each sample in a given set and eliminates the ones with greater weights in order to pick a subset of a desired size with Poisson disk property without having to specify a Poisson disk radius. This new algorithm is simple, computationally efficient, and it can work in any sampling domain, producing sample sets with more pronounced blue noise characteristics than dart throwing. Most importantly, it allows unbiased progressive (adaptive) sampling and it scales better to high dimensions than previous methods. However, it cannot guarantee maximal coverage. We provide a statistical analysis of our algorithm in 2D and higher dimensions as well as results from our tests with different example applications.
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    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.
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    A Biophysically-Based Model of the Optical Properties of Skin Aging
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Iglesias-Guitian, Jose A.; Aliaga, Carlos; Jarabo, Adrian; Gutierrez, Diego; Olga Sorkine-Hornung and Michael Wimmer
    This paper presents a time-varying, multi-layered biophysically-based model of the optical properties of human skin, suitable for simulating appearance changes due to aging. We have identified the key aspects that cause such changes, both in terms of the structure of skin and its chromophore concentrations, and rely on the extensive medical and optical tissue literature for accurate data. Our model can be expressed in terms of biophysical parameters, optical parameters commonly used in graphics and rendering (such as spectral absorption and scattering coefficients), or more intuitively with higher-level parameters such as age, gender, skin care or skin type. It can be used with any rendering algorithm that uses diffusion profiles, and it allows to automatically simulate different types of skin at different stages of aging, avoiding the need for artistic input or costly capture processes. While the presented skin model is inspired on tissue optics studies, we also provided a simplified version valid for non-diagnostic applications.
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    Panoramic Video from Unstructured Camera Arrays
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Perazzi, Federico; Sorkine-Hornung, Alexander; Zimmer, Henning; Kaufmann, Peter; Wang, Oliver; Watson, Scott; Gross, Markus; Olga Sorkine-Hornung and Michael Wimmer
    We describe an algorithm for generating panoramic video from unstructured camera arrays. Artifact-free panorama stitching is impeded by parallax between input views. Common strategies such as multi-level blending or minimum energy seams produce seamless results on quasi-static input. However, on video input these approaches introduce noticeable visual artifacts due to lack of global temporal and spatial coherence. In this paper we extend the basic concept of local warping for parallax removal. Firstly, we introduce an error measure with increased sensitivity to stitching artifacts in regions with pronounced structure. Using this measure, our method efficiently finds an optimal ordering of pair-wise warps for robust stitching with minimal parallax artifacts. Weighted extrapolation of warps in non-overlap regions ensures temporal stability, while at the same time avoiding visual discontinuities around transitions between views. Remaining global deformation introduced by the warps is spread over the entire panorama domain using constrained relaxation, while staying as close as possible to the original input views. In combination, these contributions form the first system for spatiotemporally stable panoramic video stitching from unstructured camera array input.
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    High-Order Recursive Filtering of Non-Uniformly Sampled Signals for Image and Video Processing
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Gastal, Eduardo S. L.; Oliveira, Manuel M.; Olga Sorkine-Hornung and Michael Wimmer
    We present a discrete-time mathematical formulation for applying recursive digital filters to non-uniformly sampled signals. Our solution presents several desirable features: it preserves the stability of the original filters; is well-conditioned for low-pass, high-pass, and band-pass filters alike; its cost is linear in the number of samples and is not affected by the size of the filter support. Our method is general and works with any non-uniformly sampled signal and any recursive digital filter defined by a difference equation. Since our formulation directly uses the filter coefficients, it works out-of-the-box with existing methodologies for digital filter design. We demonstrate the effectiveness of our approach by filtering non-uniformly sampled signals in various image and video processing tasks including edge-preserving color filtering, noise reduction, stylization, and detail enhancement. Our formulation enables, for the first time, edge-aware evaluation of any recursive infinite impulse response digital filter (not only low-pass), producing high-quality filtering results in real time.
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    Designing Camera Networks by Convex Quadratic Programming
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Ghanem, Bernard; Cao, Yuanhao; Wonka, Peter; Olga Sorkine-Hornung and Michael Wimmer
    In this paper, we study the problem of automatic camera placement for computer graphics and computer vision applications. We extend the problem formulations of previous work by proposing a novel way to incorporate visibility constraints and camera-to-camera relationships. For example, the placement solution can be encouraged to have cameras that image the same important locations from different viewing directions, which can enable reconstruction and surveillance tasks to perform better. We show that the general camera placement problem can be formulated mathematically as a convex binary quadratic program (BQP) under linear constraints. Moreover, we propose an optimization strategy with a favorable trade-off between speed and solution quality. Our solution is almost as fast as a greedy treatment of the problem, but the quality is significantly higher, so much so that it is comparable to exact solutions that take orders of magnitude more computation time. Because it is computationally attractive, our method also allows users to explore the space of solutions for variations in input parameters. To evaluate its effectiveness, we show a range of 3D results on real-world floorplans (garage, hotel, mall, and airport).
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    Jointly Optimized Regressors for Image Super-resolution
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Dai, Dengxin; Timofte, Radu; Gool, Luc Van; Olga Sorkine-Hornung and Michael Wimmer
    Learning regressors from low-resolution patches to high-resolution patches has shown promising results for image super-resolution. We observe that some regressors are better at dealing with certain cases, and others with different cases. In this paper, we jointly learn a collection of regressors, which collectively yield the smallest superresolving error for all training data. After training, each training sample is associated with a label to indicate its 'best' regressor, the one yielding the smallest error. During testing, our method bases on the concept of 'adaptive selection' to select the most appropriate regressor for each input patch. We assume that similar patches can be super-resolved by the same regressor and use a fast, approximate kNN approach to transfer the labels of training patches to test patches. The method is conceptually simple and computationally efficient, yet very effective. Experiments on four datasets show that our method outperforms competing methods.
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    Parallel, Realistic and Controllable Terrain Synthesis
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Gain, James; Merry, Bruce; Marais, Patrick; Olga Sorkine-Hornung and Michael Wimmer
    The challenge in terrain synthesis for virtual environments is to provide a combination of precise user control over landscape form, with interactive response and visually realistic results. We present a system that builds on parallel pixel-based texture synthesis to enable interactive creation of an output terrain from a database of heightfield exemplars. We also provide modelers with control over height and surrounding slope by means of constraint points and curves; a paint-by-numbers interface for specifying the local character of terrain; coherence controls that allow localization of changes to the synthesized terrain; and copypaste functionality to directly transplant terrain regions. Together these contributions provide a level of realism that, based on user experiments, is indistinguishable from real source terrains; user control sufficient for precise placement of a variety of landforms, such as cliffs, ravines and mesas; and synthesis times of 165ms for a 10242 terrain grid.
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    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.
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    Distilled Collections from Textual Image Queries
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Averbuch-Elor, Hadar; Wan, Yunhai; Qian, Yiming; Gong, Minglun; Kopf, Johannes; Zhang, Hao; Cohen-Or, Daniel; Olga Sorkine-Hornung and Michael Wimmer
    We present a distillation algorithm which operates on a large, unstructured, and noisy collection of internet images returned from an online object query. We introduce the notion of a distilled set, which is a clean, coherent, and structured subset of inlier images. In addition, the object of interest is properly segmented out throughout the distilled set. Our approach is unsupervised, built on a novel clustering scheme, and solves the distillation and object segmentation problems simultaneously. In essence, instead of distilling the collection of images, we distill a collection of loosely cutout foreground ''shapes'', which may or may not contain the queried object. Our key observation, which motivated our clustering scheme, is that outlier shapes are expected to be random in nature, whereas, inlier shapes, which do tightly enclose the object of interest, tend to be well supported by similar shapes captured in similar views. We analyze the commonalities among candidate foreground segments, without aiming to analyze their semantics, but simply by clustering similar shapes and considering only the most significant clusters representing non-trivial shapes. We show that when tuned conservatively, our distillation algorithm is able to extract a near perfect subset of true inliers. Furthermore, we show that our technique scales well in the sense that the precision rate remains high, as the collection grows. We demonstrate the utility of our distillation results with a number of interesting graphics applications.
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    Guiding Image Manipulations using Shape-appearance Subspaces from Co-alignment of Image Collections
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Nguyen, Chuong H.; Nalbach, Oliver; Ritschel, Tobias; Seidel, Hans-Peter; Olga Sorkine-Hornung and Michael Wimmer
    We propose a system to restrict the manipulation of shape and appearance in an image to a valid subspace which we learn from a collection of exemplar images. To this end, we automatically co-align a collection of images and learn a subspace model of shape and appearance using principal components. As finding perfect image correspondences for general images is not feasible, we build an approximate partial alignment and improve bad alignments leveraging other, more successful alignments. Our system allows the user to change appearance and shape in real-time and the result is ''projected'' onto the subspace of meaningful changes. The change in appearance and shape can either be locked or performed independently. Additional applications include suggestion of alternative shapes or appearance.
  • Item
    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.
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    Comprehensible Video Thumbnails
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Kim, Jongdae; Gray, Charles; Asente, Paul; Collomosse, John; Olga Sorkine-Hornung and Michael Wimmer
    We present the Comprehensible Video Thumbnail; an automatically generated visual précis that summarizes salient objects and their dynamics within a video clip. Salient moving objects are detected within clips using a novel stochastic sampling technique that identifies, clusters and then tracks regions exhibiting affine motion coherence within the clip. Tracks are analyzed to determine salient instants at which motion and/or appearance changes significantly, and the resulting objects arranged in a stylized composition optimized to reduce visual clutter and enhance understanding of scene content through classification and depiction of motion type and trajectory. The result is an object-level visual gist of the clip, obtained with full automation and depicting content and motion with greater descriptive power that prior approaches. We demonstrate these benefits through a user study in which the comprehension of our video thumbnails is compared to the state of the art over a wide variety of sports footage.
  • Item
    Interactive Generation of Realistic Facial Wrinkles from Sketchy Drawings
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Kim, Hyeon-Joong; Öztireli, A. Cengiz; Shin, Il-Kyu; Gross, Markus; Choi, Soo-Mi; Olga Sorkine-Hornung and Michael Wimmer
    Synthesizing facial wrinkles has been tackled either by a long process of manual sculpting on 3D models, or using automatic methods that do not allow for user interaction or artistic expression. In this paper, we propose a method that accepts interactive sketchy drawings depicting wrinkle patterns, and synthesizes realistic looking wrinkles on faces. The method inherits the simplicity of sketching, making it possible for artists as well as novice users to generate realistic facial detail very efficiently, allowing fast preview for physical makeup, or aging simulations for fun and professional applications. All strokes are used to infer the wrinkles, retaining the expressiveness of the sketches and realism of the final result at the same time. This is achieved by designing novel multi-scale statistics tailored to the wrinkle geometry and coupled to the sketch interpretation method. The statistics capture the crosssectional profiles of wrinkles at different scales and parts of a face. The strokes are augmented with the statistics extracted from given example face models, and applied to an input face model interactively. The interface gives the user control over the shapes and scales of wrinkles via sketching while adding extra details required for realism automatically.
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    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.
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    Layer-Based Procedural Design of Façades
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Ilcík, Martin; Musialski, Przemyslaw; Auzinger, Thomas; Wimmer, Michael; Olga Sorkine-Hornung and Michael Wimmer
    We present a novel procedural framework for interactively modeling building façades. Common procedural approaches, such as shape grammars, assume that building façades are organized in a tree structure, while in practice this is often not the case. Consequently, the complexity of their layout description becomes unmanageable for interactive editing. In contrast, we obtain a façade by composing multiple overlapping layers, where each layer contains a single rectilinear grid of façade elements described by two simple generator patterns. This way, the design process becomes more intuitive and the editing effort for complex layouts is significantly reduced. To achieve this, we present a method for the automated merging of different layers in the form of a mixed discrete and continuous optimization problem. Finally, we provide several modeling examples and a comparison to shape grammars in order to highlight the advantages of our method when designing realistic building façades.
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    Template Assembly for Detailed Urban Reconstruction
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Nan, Liangliang; Jiang, Caigui; Ghanem, Bernard; Wonka, Peter; Olga Sorkine-Hornung and Michael Wimmer
    We propose a new framework to reconstruct building details by automatically assembling 3D templates on coarse textured building models. In a preprocessing step, we generate an initial coarse model to approximate a point cloud computed using Structure from Motion and Multi View Stereo, and we model a set of 3D templates of facade details. Next, we optimize the initial coarse model to enforce consistency between geometry and appearance (texture images). Then, building details are reconstructed by assembling templates on the textured faces of the coarse model. The 3D templates are automatically chosen and located by our optimization-based template assembly algorithm that balances image matching and structural regularity. In the results, we demonstrate how our framework can enrich the details of coarse models using various data sets.
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    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.
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    Approximating Free-form Geometry with Height Fields for Manufacturing
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Herholz, Philipp; Matusik, Wojciech; Alexa, Marc; Olga Sorkine-Hornung and Michael Wimmer
    We consider the problem of manufacturing free-form geometry with classical manufacturing techniques, such as mold casting or 3-axis milling. We determine a set of constraints that are necessary for manufacturability and then decompose and, if necessary, deform the shape to satisfy the constraints per segment. We show that many objects can be generated from a small number of (mold-)pieces if slight deformations are acceptable. We provide examples of actual molds and the resulting manufactured objects.
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    High Reliefs from 3D Scenes
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Arpa, Sami; Süsstrunk, Sabine; Hersch, Roger D.; Olga Sorkine-Hornung and Michael Wimmer
    We present a method for synthesizing high reliefs, a sculpting technique that attaches 3D objects onto a 2D surface within a limited depth range. The main challenges are the preservation of distinct scene parts by preserving depth discontinuities, the fine details of the shape, and the overall continuity of the scene. Bas relief depth compression methods such as gradient compression and depth range compression are not applicable for high relief production. Instead, our method is based on differential coordinates to bring scene elements to the relief plane while preserving depth discontinuities and surface details of the scene. We select a user-defined number of attenuation points within the scene, attenuate these points towards the relief plane and recompute the positions of all scene elements by preserving the differential coordinates. Finally, if the desired depth range is not achieved we apply a range compression. High relief synthesis is semi-automatic and can be controlled by user-defined parameters to adjust the depth range, as well as the placement of the scene elements with respect to the relief plane.
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    Shape-from-Operator: Recovering Shapes from Intrinsic Operators
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Boscaini, Davide; Eynard, Davide; Kourounis, Drosos; Bronstein, Michael M.; Olga Sorkine-Hornung and Michael Wimmer
    We formulate the problem of shape-from-operator (SfO), recovering an embedding of a mesh from intrinsic operators defined through the discrete metric (edge lengths). Particularly interesting instances of our SfO problem include: shape-from-Laplacian, allowing to transfer style between shapes; shape-from-difference operator, used to synthesize shape analogies; and shape-from-eigenvectors, allowing to generate 'intrinsic averages' of shape collections. Numerically, we approach the SfO problem by splitting it into two optimization sub-problems: metric-from-operator (reconstruction of the discrete metric from the intrinsic operator) and embedding-from-metric (finding a shape embedding that would realize a given metric, a setting of the multidimensional scaling problem). We study numerical properties of our problem, exemplify it on several applications, and discuss its imitations.
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    Skeleton-Intrinsic Symmetrization of Shapes
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Zheng, Qian; Hao, Zhuming; Huang, Hui; Xu, Kai; Zhang, Hao; Cohen-Or, Daniel; Chen, Baoquan; Olga Sorkine-Hornung and Michael Wimmer
    Enhancing the self-symmetry of a shape is of fundamental aesthetic virtue. In this paper, we are interested in recovering the aesthetics of intrinsic reflection symmetries, where an asymmetric shape is symmetrized while keeping its general pose and perceived dynamics. The key challenge to intrinsic symmetrization is that the input shape has only approximate reflection symmetries, possibly far from perfect. The main premise of our work is that curve skeletons provide a concise and effective shape abstraction for analyzing approximate intrinsic symmetries as well as symmetrization. By measuring intrinsic distances over a curve skeleton for symmetry analysis, symmetrizing the skeleton, and then propagating the symmetrization from skeleton to shape, our approach to shape symmetrization is skeleton-intrinsic. Specifically, given an input shape and an extracted curve skeleton, we introduce the notion of a backbone as the path in the skeleton graph about which a self-matching of the input shape is optimal. We define an objective function for the reflective self-matching and develop an algorithm based on genetic programming to solve the global search problem for the backbone. The extracted backbone then guides the symmetrization of the skeleton, which in turn, guides the symmetrization of the whole shape. We show numerous intrinsic symmetrization results of hand drawn sketches and artist-modeled or reconstructed 3D shapes, as well as several applications of skeleton-intrinsic symmetrization of shapes.
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    Interactive Disassembly Planning for Complex Objects
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Kerbl, Bernhard; Kalkofen, Denis; Steinberger, Markus; Schmalstieg, Dieter; Olga Sorkine-Hornung and Michael Wimmer
    We present an approach for the automatic generation, interactive exploration and real-time modification of disassembly procedures for complex, multipartite CAD data sets. In order to lift the performance barriers prohibiting interactive disassembly planning, we run a detailed analysis on the input model to identify recurring part constellations and efficiently determine blocked part motions in parallel on the GPU. Building on the extracted information, we present an interface for computing and editing extensive disassembly sequences in real-time while considering user-defined constraints and avoiding unstable configurations. To evaluate the performance of our C++/CUDA implementation, we use a variety of openly available CAD data sets, ranging from simple to highly complex. In contrast to previous approaches, our work enables interactive disassembly planning for objects which consist of several thousand parts and require cascaded translations during part removal.
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    Approximating the Generalized Voronoi Diagram of Closely Spaced Objects
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Edwards, John; Daniel, Eric; Pascucci, Valerio; Bajaj, Chandrajit; Olga Sorkine-Hornung and Michael Wimmer
    We present an algorithm to compute an approximation of the generalized Voronoi diagram (GVD) on arbitrary collections of 2D or 3D geometric objects. In particular, we focus on datasets with closely spaced objects; GVD approximation is expensive and sometimes intractable on these datasets using previous algorithms. With our approach, the GVD can be computed using commodity hardware even on datasets with many, extremely tightly packed objects. Our approach is to subdivide the space with an octree that is represented with an adjacency structure. We then use a novel adaptive distance transform to compute the distance function on octree vertices. The computed distance field is sampled more densely in areas of close object spacing, enabling robust and parallelizable GVD surface generation. We demonstrate our method on a variety of data and show example applications of the GVD in 2D and 3D.
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    Hardware-Based Non-Photorealistic Rendering Using a Painting Robot
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Lindemeier, Thomas; Metzner, Jens; Pollak, Lena; Deussen, Oliver; Olga Sorkine-Hornung and Michael Wimmer
    We describe a painting machine and associated algorithms. Our modified industrial robot works with visual feedback and applies acrylic paint from a repository to a canvas until the created painting resembles a given input image or scene. The color differences between canvas and input are used to direct the application of new strokes. We present two optimization-based algorithms that place such strokes in relation to already existing ones. Using these methods we are able to create different painting styles, one that tries to match the input colors with almost transparent strokes and another one that creates dithering patterns of opaque strokes that approximate the input color. The machine produces paintings that mimic those created by human painters and allows us to study the painting process as well as the creation of artworks.
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    Light Chisel: 6DOF Pen Tracking
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Bubník, Vojtech; Havran, Vlastimil; Olga Sorkine-Hornung and Michael Wimmer
    We present a novel interaction device tracked in 6 degrees of freedom by two commodity cameras. The inexpensive Light Chisel is statically illuminated with two LEDs, and uses no additional sensor (e.g. inertial or magnetic) or means of communication or synchronization. Its form factor is well suited for a screwdriver or chisel grip, allowing the Light Chisel to be rolled between the fingers. The position and orientation of the tool is tracked absolutely, making the Light Chisel suited for complex interaction, e.g. geometric modeling in augmented reality. The Light Chisel is physically small, limiting the physical and optical collisions with the real world. The orientation of the tool is tracked in a wide range of angles: pitch and yaw 90 , roll 180 . We evaluated our system against the OptiTrack optical tracking system. Our system achieved mean differences from OptiTrack reference of 2:07mm in position, 1:06 in yaw and pitch, and 5:26 in roll using a pair of VGA cameras. We demonstrate usefulness of our Light Chisel in four applications: character animation, modeling by swirls, volumetric modeling, and docking of CAD models.
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    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.
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    Self Tuning Texture Optimization
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Kaspar, Alexandre; Neubert, Boris; Lischinski, Dani; Pauly, Mark; Kopf, Johannes; Olga Sorkine-Hornung and Michael Wimmer
    The goal of example-based texture synthesis methods is to generate arbitrarily large textures from limited exemplars in order to fit the exact dimensions and resolution required for a specific modeling task. The challenge is to faithfully capture all of the visual characteristics of the exemplar texture, without introducing obvious repetitions or unnatural looking visual elements. While existing non-parametric synthesis methods have made remarkable progress towards this goal, most such methods have been demonstrated only on relatively low-resolution exemplars. Real-world high resolution textures often contain texture details at multiple scales, which these methods have difficulty reproducing faithfully. In this work, we present a new general-purpose and fully automatic selftuning non-parametric texture synthesis method that extends Texture Optimization by introducing several key improvements that result in superior synthesis ability. Our method is able to self-tune its various parameters and weights and focuses on addressing three challenging aspects of texture synthesis: (i) irregular large scale structures are faithfully reproduced through the use of automatically generated and weighted guidance channels; (ii) repetition and smoothing of texture patches is avoided by new spatial uniformity constraints; (iii) a smart initialization strategy is used in order to improve the synthesis of regular and near-regular textures, without affecting textures that do not exhibit regularities. We demonstrate the versatility and robustness of our completely automatic approach on a variety of challenging high-resolution texture exemplars.
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    Woodification: User-Controlled Cambial Growth Modeling
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Kratt, Julian; Spicker, Marc; Guayaquil, Alejandro; Fiser, Marek; Pirk, Sören; Deussen, Oliver; Hart, John C.; Benes, Bedrich; Olga Sorkine-Hornung and Michael Wimmer
    We present a botanical simulation of secondary (cambial) tree growth coupled to a physical cracking simulation of its bark. Whereas level set growth would use a fixed resolution voxel grid, our system extends the deformable simplicial complex (DSC), supporting new biological growth functions robustly on any surface polygonal mesh with adaptive subdivision, collision detection and topological control.We extend the DSC with temporally coherent texturing, and surface cracking with a user-controllable biological model coupled to the stresses introduced by the cambial growth model.
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    Color Sequence Preserving Decolorization
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Yoo, Min-Joon; Lee, In-Kwon; Lee, Seungyong; Olga Sorkine-Hornung and Michael Wimmer
    Many visualization techniques use images containing meaningful color sequences. If such images are converted to grayscale, the sequence is often distorted, compromising the information in the image.We preserve the significance of a color sequence during decolorization by mapping the colors from a source image to a grid in the CIELAB color space. We then identify the most significant hues, and thin the corresponding cells of the grid to approximate a curve in the color space, eliminating outliers using a weighted Laplacian eigenmap. This curve is then mapped to a monotonic sequence of gray levels. The saturation values of the resulting image are combined with the original intensity channels to restore details such as text. Our approach can also be used to recolor images containing color sequences, for instance for viewers with color-deficient vision, or to interpolate between two images that use the same geometry and color sequence to present different data.
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    Real-Time Subspace Integration for Example-Based Elastic Material
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhang, Wenjing; Zheng, Jianmin; Thalmann, Nadia Magnenat; Olga Sorkine-Hornung and Michael Wimmer
    Example-based material allows simulating complex material behaviors in an art-directed way. This paper presents a method for fast subspace integration for example-based elastic material, which is suitable for real-time simulation in computer graphics. At the core of the method is the formulation of a new potential using example-based Green strain tensors. By using this potential, the deformation can be attracted towards the example-based deformation feature space, the example weights can be explicitly obtained and the internal force can be decomposed into the conventional one and an additional one induced by the examples. The real-time subspace integration is then developed with subspace integration costs independent of geometric complexity, and both the reduced conventional internal force and additional one being cubic polynomials in reduced coordinates. Experiments demonstrate that our method can achieve real-time simulation while providing comparable quality with the prior art.
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    Paint and Click: Unified Interactions for Image Boundaries
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Summa, Brian; Gooch, Amy A.; Scorzelli, Giorgio; Pascucci, Valerio; Olga Sorkine-Hornung and Michael Wimmer
    Image boundaries are a fundamental component of many interactive digital photography techniques, enabling applications such as segmentation, panoramas, and seamless image composition. Interactions for image boundaries often rely on two complementary but separate approaches: editing via painting or clicking constraints. In this work, we provide a novel, unified approach for interactive editing of pairwise image boundaries that combines the ease of painting with the direct control of constraints. Rather than a sequential coupling, this new formulation allows full use of both interactions simultaneously, giving users unprecedented flexibility for fast boundary editing. To enable this new approach, we provide technical advancements. In particular, we detail a reformulation of image boundaries as a problem of finding cycles, expanding and correcting limitations of the previous work. Our new formulation provides boundary solutions for painted regions with performance on par with state-of-the-art specialized, paint-only techniques. In addition, we provide instantaneous exploration of the boundary solution space with user constraints. Finally, we provide examples of common graphics applications impacted by our new approach.
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    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.
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    Improving Sampling-based Motion Control
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Liu, Libin; Yin, KangKang; Guo, Baining; Olga Sorkine-Hornung and Michael Wimmer
    We address several limitations of the sampling-based motion control method of Liu et at. [LYvdP 10]. The key insight is to learn from the past control reconstruction trials through sample distribution adaptation. Coupled with a sliding window scheme for better performance and an averaging method for noise reduction, the improved algorithm can efficiently construct open-loop controls for long and challenging reference motions in good quality. Our ideas are intuitive and the implementations are simple. We compare the improved algorithm with the original algorithm both qualitatively and quantitatively, and demonstrate the effectiveness of the improved algorithm with a variety of motions ranging from stylized walking and dancing to gymnastic and Martial Arts routines.
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    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.
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    Database-Assisted Object Retrieval for Real-Time 3D Reconstruction
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Li, Yangyan; Dai, Angela; Guibas, Leonidas; Nießner, Matthias; Olga Sorkine-Hornung and Michael Wimmer
    In recent years, real-time 3D scanning technology has developed significantly and is now able to capture large environments with considerable accuracy. Unfortunately, the reconstructed geometry still suffers from incompleteness, due to occlusions and lack of view coverage, resulting in unsatisfactory reconstructions. In order to overcome these fundamental physical limitations, we present a novel reconstruction approach based on retrieving objects from a 3D shape database while scanning an environment in real-time. With this approach, we are able to replace scanned RGB-D data with complete, hand-modeled objects from shape databases. We align and scale retrieved models to the input data to obtain a high-quality virtual representation of the real-world environment that is quite faithful to the original geometry. In contrast to previous methods, we are able to retrieve objects in cluttered and noisy scenes even when the database contains only similar models, but no exact matches. In addition, we put a strong focus on object retrieval in an interactive scanning context —- our algorithm runs directly on 3D scanning data structures, and is able to query databases of thousands of models in an online fashion during scanning.
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    SmartAnnotator: An Interactive Tool for Annotating Indoor RGBD Images
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Wong, Yu-Shiang; Chu, Hung-Kuo; Mitra, Niloy J.; Olga Sorkine-Hornung and Michael Wimmer
    RGBD images with high quality annotations, both in the form of geometric (i.e., segmentation) and structural (i.e., how do the segments mutually relate in 3D) information, provide valuable priors for a diverse range of applications in scene understanding and image manipulation. While it is now simple to acquire RGBD images, annotating them, automatically or manually, remains challenging. We present SMARTANNOTATOR, an interactive system to facilitate annotating raw RGBD images. The system performs the tedious tasks of grouping pixels, creating potential abstracted cuboids, inferring object interactions in 3D, and generates an ordered list of hypotheses. The user simply has to flip through the suggestions for segment labels, finalize a selection, and the system updates the remaining hypotheses. As annotations are finalized, the process becomes simpler with fewer ambiguities to resolve. Moreover, as more scenes are annotated, the system makes better suggestions based on the structural and geometric priors learned from previous annotation sessions. We test the system on a large number of indoor scenes across different users and experimental settings, validate the results on existing benchmark datasets, and report significant improvements over low-level annotation alternatives. (Code and benchmark datasets are publicly available on the project page.)
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    Adaptable Anatomical Models for Realistic Bone Motion Reconstruction
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhu, Lifeng; Hu, Xiaoyan; Kavan, Ladislav; Olga Sorkine-Hornung and Michael Wimmer
    We present a system to reconstruct subject-specific anatomy models while relying only on exterior measurements represented by point clouds. Our model combines geometry, kinematics, and skin deformations (skinning). This joint model can be adapted to different individuals without breaking its functionality, i.e., the bones and the skin remain well-articulated after the adaptation.We propose an optimization algorithm which learns the subject-specific (anthropometric) parameters from input point clouds captured using commodity depth cameras. The resulting personalized models can be used to reconstruct motion of human subjects. We validate our approach for upper and lower limbs, using both synthetic data and recordings of three different human subjects. Our reconstructed bone motion is comparable to results obtained by optical motion capture (Vicon) combined with anatomically-based inverse kinematics (OpenSIM). We demonstrate that our adapted models better preserve the joint structure than previous methods such as OpenSIM or Anatomy Transfer.
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    A Dimension-reduced Pressure Solver for Liquid Simulations
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Ando, Ryoichi; Thürey, Nils; Wojtan, Chris; Olga Sorkine-Hornung and Michael Wimmer
    This work presents a method for efficiently simplifying the pressure projection step in a liquid simulation. We first devise a straightforward dimension reduction technique that dramatically reduces the cost of solving the pressure projection. Next, we introduce a novel change of basis that satisfies free-surface boundary conditions exactly, regardless of the accuracy of the pressure solve. When combined, these ideas greatly reduce the computational complexity of the pressure solve without compromising free surface boundary conditions at the highest level of detail. Our techniques are easy to parallelize, and they effectively eliminate the computational bottleneck for large liquid simulations.
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    A Cut-Cell Geometric Multigrid Poisson Solver for Fluid Simulation
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Weber, Daniel; Mueller-Roemer, Johannes; Stork, André; Fellner, Dieter W.; Olga Sorkine-Hornung and Michael Wimmer
    We present a novel multigrid scheme based on a cut-cell formulation on regular staggered grids which generates compatible systems of linear equations on all levels of the multigrid hierarchy. This geometrically motivated formulation is derived from a finite volume approach and exhibits an improved rate of convergence compared to previous methods. Existing fluid solvers with voxelized domains can directly benefit from this approach by only modifying the representation of the non-fluid domain. The necessary building blocks are fully parallelizable and can therefore benefit from multi- and many-core architectures.
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    Implicit Formulation for SPH-based Viscous Fluids
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Takahashi, Tetsuya; Dobashi, Yoshinori; Fujishiro, Issei; Nishita, Tomoyuki; Lin, Ming C.; Olga Sorkine-Hornung and Michael Wimmer
    We propose a stable and efficient particle-based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second-ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method.
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    Replaceable Substructures for Efficient Part-Based Modeling
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Liu, Han; Vimont, Ulysse; Wand, Michael; Cani, Marie-Paule; Hahmann, Stefanie; Rohmer, Damien; Mitra, Niloy J.; Olga Sorkine-Hornung and Michael Wimmer
    A popular mode of shape synthesis involves mixing and matching parts from different objects to form a coherent whole. The key challenge is to efficiently synthesize shape variations that are plausible, both locally and globally. A major obstacle is to assemble the objects with local consistency, i.e., all the connections between parts are valid with no dangling open connections. The combinatorial complexity of this problem limits existing methods in geometric and/or topological variations of the synthesized models. In this work, we introduce replaceable substructures as arrangements of parts that can be interchanged while ensuring boundary consistency. The consistency information is extracted from part labels and connections in the original source models. We present a polynomial time algorithm that discovers such substructures by working on a dual of the original shape graph that encodes inter-part connectivity. We demonstrate the algorithm on a range of test examples producing plausible shape variations, both from a geometric and from a topological viewpoint.
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    Generating Design Suggestions under Tight Constraints with Gradient-based Probabilistic Programming
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Ritchie, Daniel; Lin, Sharon; Goodman, Noah D.; Hanrahan, Pat; Olga Sorkine-Hornung and Michael Wimmer
    We present a system for generating suggestions from highly-constrained, continuous design spaces. We formulate suggestion as sampling from a probability distribution; constraints are represented as factors that concentrate probability mass around sub-manifolds of the design space. These sampling problems are intractable using typical random walk MCMC techniques, so we adopt Hamiltonian Monte Carlo (HMC), a gradient-based MCMC method. We implement HMC in a high-performance probabilistic programming language, and we evaluate its ability to efficiently generate suggestions for two different, highly-constrained example applications: vector art coloring and designing stable stacking structures.
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    T-SAH: Animation Optimized Bounding Volume Hierarchies
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Bittner, Jirí; Meister, Daniel; Olga Sorkine-Hornung and Michael Wimmer
    We propose a method for creating a bounding volume hierarchy (BVH) that is optimized for all frames of a given animated scene. The method is based on a novel extension of surface area heuristic to temporal domain (T-SAH). We perform iterative BVH optimization using T-SAH and create a single BVH accounting for scene geometry distribution at different frames of the animation. Having a single optimized BVH for the whole animation makes our method extremely easy to integrate to any application using BVHs, limiting the per-frame overhead only to refitting the bounding volumes.We evaluated the T-SAH optimized BVHs in the scope of real-time GPU ray tracing. We demonstrate, that our method can handle even highly complex inputs with large deformations and significant topology changes. The results show, that in a vast majority of tested scenes our method provides significantly better run-time performance than traditional SAH and also better performance than GPU based per-frame BVH rebuild.
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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.
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    Partitioned Shadow Volumes
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Gerhards, Julien; Mora, Frédéric; Aveneau, Lilian; Ghazanfarpour, Djamchid; Olga Sorkine-Hornung and Michael Wimmer
    Real-time shadows remain a challenging problem in computer graphics. In this context, shadow algorithms generally rely either on shadow mapping or shadow volumes. This paper rediscovers an old class of algorithms that build a binary space partition over the shadow volumes. For almost 20 years, such methods have received little attention as they have been considered lacking of both robustness and efficiency. We show that these issues can be overcome, leading to a simple and robust shadow algorithm. Hence we demonstrate that this kind of approach can reach a high level of performance. Our algorithm uses a new partitioning strategy which avoids any polygon clipping. It relies on a Ternary Object Partitioning tree, a new data structure used to find if an image point is shadowed. Our method works on a triangle soup and its memory footprint is fixed. Our experiments show that it is efficient and robust, including for finely tessellated models.
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    IlluminationCut
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Bus, Norbert; Mustafa, Nabil H.; Biri, Venceslas; Olga Sorkine-Hornung and Michael Wimmer
    We present a novel algorithm, IlluminationCut, for rendering images using the many-lights framework. It handles any light source that can be approximated with virtual point lights (VPLs) as well as highly glossy materials. The algorithm extends the Multidimensional Lightcuts technique by effectively creating an illumination-aware clustering of the product-space of the set of points to be shaded and the set of VPLs. Additionally, the number of visibility queries for each product-space cluster is reduced by using an adaptive sampling technique. Our framework is flexible and achieves around 3 - 6 times speedup over previous state-of-the-art methods.
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    Rich-VPLs for Improving the Versatility of Many-Light Methods
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Simon, Florian; Hanika, Johannes; Dachsbacher, Carsten; Olga Sorkine-Hornung and Michael Wimmer
    Many-light methods approximate the light transport in a scene by computing the direct illumination from many virtual point light sources (VPLs), and render low-noise images covering a wide range of performance and quality goals. However, they are very inefficient at representing glossy light transport. This is because a VPL on a glossy surface illuminates a small fraction of the scene only, and a tremendous number of VPLs might be necessary to render acceptable images. In this paper, we introduce Rich-VPLs which, in contrast to standard VPLs, represent a multitude of light paths and thus have a more widespread emission profile on glossy surfaces and in scenes with multiple primary light sources. By this, a single Rich-VPL contributes to larger portions of a scene with negligible additional shading cost. Our second contribution is a placement strategy for (Rich-)VPLs proportional to sensor importance times radiance. Although both Rich-VPLs and improved placement can be used individually, they complement each other ideally and share interim computation. Furthermore, both complement existing manylight methods, e.g. Lightcuts or the Virtual Spherical Lights method, and can improve their efficiency as well as their application for scenes with glossy materials and many primary light sources.
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    Robust Statistical Pixel Estimation
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Jung, Jin Woo; Meyer, Gary; DeLong, Ralph; Olga Sorkine-Hornung and Michael Wimmer
    Robust statistical methods are employed to reduce the noise in Monte Carlo ray tracing. Through the use of resampling, the sample mean distribution is determined for each pixel. Because this distribution is uni-modal and normal for a large sample size, robust estimates converge to the true mean of the pixel values. Compared to existing methods, less additional storage is required at each pixel because the sample mean distribution can be distilled down to a compact size, and fewer computations are necessary because the robust estimation process is sampling independent and needs a small input size to compute pixel values. The robust statistical pixel estimators are not only resistant to impulse noise, but they also remove general noise from fat-tailed distributions. A substantial speedup in rendering can therefore be achieved by reducing the number of samples required for a desired image quality. The effectiveness of the proposed approach is demonstrated for path tracing simulations.
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    General and Robust Error Estimation and Reconstruction for Monte Carlo Rendering
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Bauszat, Pablo; Eisemann, Martin; Eisemann, Elmar; Magnor, Marcus; Olga Sorkine-Hornung and Michael Wimmer
    Adaptive filtering techniques have proven successful in handling non-uniform noise in Monte-Carlo rendering approaches. A recent trend is to choose an optimal filter per pixel from a selection of non spatially-varying filters. Nonetheless, the best filter choice is difficult to predict in the absence of a reference rendering. Our approach relies on the observation that the reconstruction error is locally smooth for a given filter. Hence, we propose to construct a dense error prediction from a small set of sparse but robust estimates. The filter selection is then formulated as a non-local optimization problem, which we solve via graph cuts, to avoid visual artifacts due to inconsistent filter choices. Our approach does not impose any restrictions on the used filters, outperforms previous state-of-the-art techniques and provides an extensible framework for future reconstruction techniques.
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    Selective Degree Elevation for Multi-Sided Bézier Patches
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Smith, Jason; Schaefer, Scott; Olga Sorkine-Hornung and Michael Wimmer
    This paper presents a method to selectively elevate the degree of an S-Patch of arbitrary dimension. We consider not only S-Patches with 2D domains but 3D and higher-dimensional domains as well, of which volumetric cage deformations are a subset. We show how to selectively insert control points of a higher degree patch into a lower degree patch while maintaining the polynomial reproduction order of the original patch. This process allows the user to elevate the degree of only one portion of the patch to add new degrees of freedom or maintain continuity with adjacent patches without elevating the degree of the entire patch, which could create far more degrees of freedom than necessary. Finally we show an application to cage-based deformations where we increase the number of control points by elevating the degree of a subset of cage faces. The result is a cage deformation with higher degree triangular Bézier functions on a subset of cage faces but no interior control points.
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    Statics Aware Grid Shells
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Pietroni, Nico; Tonelli, Davide; Puppo, Enrico; Froli, Maurizio; Scopigno, Roberto; Cignoni, Paolo; Olga Sorkine-Hornung and Michael Wimmer
    We introduce a framework for the generation of polygonal grid-shell architectural structures, whose topology is designed in order to excel in static performances. We start from the analysis of stress on the input surface and we use the resulting tensor field to induce an anisotropic non-Euclidean metric over it. This metric is derived by studying the relation between the stress tensor over a continuous shell and the optimal shape of polygons in a corresponding grid-shell. Polygonal meshes with uniform density and isotropic cells under this metric exhibit variable density and anisotropy in Euclidean space, thus achieving a better distribution of the strain energy over their elements. Meshes are further optimized taking into account symmetry and regularity of cells to improve aesthetics. We experiment with quad meshes and hex-dominant meshes, demonstrating that our grid-shells achieve better static performances than state-of-the-art grid-shells.
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    Optimal Spline Approximation via l0-Minimization
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Brandt, Christopher; Seidel, Hans-Peter; Hildebrandt, Klaus; Olga Sorkine-Hornung and Michael Wimmer
    Splines are part of the standard toolbox for the approximation of functions and curves in Rd. Still, the problem of finding the spline that best approximates an input function or curve is ill-posed, since in general this yields a ''spline'' with an infinite number of segments. The problem can be regularized by adding a penalty term for the number of spline segments. We show how this idea can be formulated as an 0-regularized quadratic problem. This gives us a notion of optimal approximating splines that depend on one parameter, which weights the approximation error against the number of segments. We detail this concept for different types of splines including B-splines and composite Bézier curves. Based on the latest development in the field of sparse approximation, we devise a solver for the resulting minimization problems and show applications to spline approximation of planar and space curves and to spline conversion of motion capture data.
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    EUROGRAPHICS 2015: CGF 34-2 Frontmatter
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Olga Sorkine-Hornung; Michael Wimmer;