EG 2016 - Full Papers - CGF 35-Issue 2
Permanent URI for this collection
Shape M&M
Fast and Robust Inversion-Free Shape Manipulation
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Tiantian Liu, Ming Gao, Lifeng Zhu, Eftychios Sifakis, and Ladislav Kavan
Building Construction Sets by Tiling Grammar Simplification
Javor Kalojanov, Michael Wand, and Philipp Slusallek
Editing, Sketch & Drawing
Structure-adaptive Shape Editing for Man-made Objects
Qiang Fu, Xiaowu Chen, Xiaoyu Su, Jia Li, and Hongbo Fu
SMARTCANVAS: Context-inferred Interpretation of Sketches for Preparatory Design Studies
Youyi Zheng, Han Liu, Julie Dorsey, and Niloy J. Mitra
Fabrication
Buoyancy Optimization for Computational Fabrication
Lingfeng Wang and Emily Whiting
Improved Surface Quality in 3D Printing by Optimizing the Printing Direction
Weiming Wang, Cédric Zanni, and Leif Kobbelt
Image Editing & Processing
Generalized Diffusion Curves: An Improved Vector Representation for Smooth-Shaded Images
Stefan Jeschke
Generalized As-Similar -As-Possible Warping with Applications in Digital Photography
Renjie Chen and Craig Gotsman
Automatic Portrait Segmentation for Image Stylization
Xiaoyong Shen, Aaron Hertzmann, Jiaya Jia, Sylvain Paris, Brian Price, Eli Shechtman, and
Ian Sachs
Character Animation
Motion Grammars for Character Animation
Kyunglyul Hyun, Kyungho Lee, and Jehee Lee
Animation Setup Transfer for 3D Characters
Quentin Avril, Donya Ghafourzadeh, Srinivasan Ramachandran, Sahel Fallahdoust, Sarah Ribet,
Olivier Dionne, Martin de Lasa, and Eric Paquette
Character Contact Re-positioning Under Large Environment Deformation
Steve Tonneau, Rami Ali Al-Ashqar, Julien Pettré, Taku Komura, and Nicolas Mansard
HDR Imaging
An Objective Deghosting Quality Metric for HDR Images
Okan Tarhan Tursun, Ahmet Oğuz Akyüz, Aykut Erdem, and Erkut Erdem
Convolutional Sparse Coding for High Dynamic Range Imaging
Ana Serrano, Felix Heide, Diego Gutierrez, Gordon Wetzstein, and Belen Masia
Terrains & Fluids
Large Scale Terrain Generation from Tectonic Uplift and Fluvial Erosion
Guillaume Cordonnier, Jean Braun, Marie-Paule Cani, Bedrich Benes, Éric Galin, Adrien
Peytavie, and Éric Guérin
Sparse Representation of Terrains for Procedural Modeling
Eric Guérin, Julie Digne, Eric Galin, and Adrien Peytavie
Data-driven Images
DeepProp: Extracting Deep Features from a Single Image for Edit Propagation
Yuki Endo, Satoshi Iizuka, Yoshihiro Kanamori, and Jun Mitani
Smooth Image Sequences for Data-driven Morphing
Hadar Elor, Daniel Cohen-Or, and Johannes Kopf
Fluid Simulation
Boundary Detection in Particle-based Fluids
Marcos Sandim, Douglas Cedrim, Luis Gustavo Nonato, Paulo Pagliosa, and Afonso Paiva
Narrow Band FLIP for Liquid Simulations
Florian Ferstl, Ryoichi Ando, Chris Wojtan, Rüdiger Westermann, and Nils Thuerey
A Practical Method for High-Resolution Embedded Liquid Surfaces
Ryan Goldade, Christopher Batty, and Chris Wojtan
Global Illumination
Stylized Caustics: Progressive Rendering of Animated Caustics
Tobias Günther, Kai Rohmer, Christian Rössl, Thorsten Grosch, and Holger Theisel
Meshes
Multi-Resolution Meshes for Feature-Aware Hardware Tessellation
Thibaud Lambert, Pierre Bénard, and Gaël Guennebaud
Rendering Techniques
Regularizing Image Reconstruction for Gradient-Domain Rendering with Feature Patches
Marco Manzi, Delio Vicini, and Matthias Zwicker
A Practical and Controllable Hair and Fur Model for Production Path Tracing
Matt Jen-Yuan Chiang, Benedikt Bitterli, Chuck Tappan, and Brent Burley
SAH Guided Spatial Split Partitioning for Fast BVH Construction
Per Ganestam and Michael Doggett
Curves & Surfaces
Geometric Flows of Curves in Shape Space for Processing Motion of Deformable Objects
Christopher Brandt, Christoph von Tycowicz, and Klaus Hildebrandt
A Multi-sided Bézier Patch with a Simple Control Structure
Tamás Várady, Péter Salvi, and György Karikó
Adapting Feature Curve Networks to a Prescribed Scale
Anne Gehre, Isaak Lim, and Leif Kobbelt
Shadows
Compressed Multiresolution Hierarchies for High-Quality Precomputed Shadows
Leonardo Scandolo, Pablo Bauszat, and Elmar Eisemann
Faces & Motion
BlendForces: A Dynamic Framework for Facial Animation
Vincent Barrielle, Nicolas Stoiber, and Cédric Cagniart
Near-Instant Capture of High-Resolution Facial Geometry and Reflectance
Graham Fyffe, Paul Graham, Borom Tunwattanapong, Abhijeet Ghosh, and Paul Debevec
Deformable & Soft Objects
Learning 3D Deformation of Animals from 2D Images
Angjoo Kanazawa, Shahar Kovalsky, Ronen Basri, and David Jacobs
Effect of Low-level Visual Details in Perception of Deformation
Donghui Han and John Keyser
Modeling and Estimation of Energy-Based Hyperelastic Objects
Eder Miguel, David Miraut, and Miguel A. Otaduy
Texturing & Compression
Geometry and Attribute Compression for Voxel Scenes
Bas Dado, Timothy R. Kol, Pablo Bauszat, Jean-Marc Thiery, and Elmar Eisemann
VBTC: GPU-Friendly Variable Block Size Texture Encoding
Pavel Krajcevski, Abhinav Golas, Karthik Ramani, Michael Shebanow, and Dinesh Manocha
Geometric Modeling
Space-Time Co-Segmentation of Articulated Point Cloud Sequences
Qing Yuan, Guiqing Li, Kai Xu, Xudong Chen, and Hui Huang
Anisotropic Diffusion Descriptors
Davide Boscaini, Jonathan Masci, Emanuele Rodolà , Michael M. Bronstein, Daniel Cremers
Visualization
General Projective Maps for Multidimensional Data Projection
Dirk J. Lehmann and Holger Theisel
Inertial Steady 2D Vector Field Topology
Tobias Günther and Holger Theisel
Video
Multisampling Compressive Video Spectroscopy
Daniel S. Jeon, Inchang Choi, Min H. Kim
Seamless Video Stitching from Hand-held Camera Inputs
Kaimo Lin, Shuaicheng Liu, Loong-Fah Cheong, and Bing Zeng
Interactive Videos: Plausible Video Editing using Sparse Structure Points
Chia Sheng Chang, Hung-Kuo Chu, and Niloy J. Mitra
Images & Geometry
Single Image Weathering via Exemplar Propagation
Satoshi Iizuka, Yuki Endo, Yoshihiro Kanamori, and Jun Mitani
Cloth & Animation
CAMA: Contact-Aware Matrix Assembly with Unified Collision Handling for GPU-based Cloth
Simulation
Min Tang, Huamin Wang, Le Tang, Ruofeng Tong, and Dinesh Manocha
Dexterous Manipulation of Cloth
Yunfei Bai, Wenhao Yu, and C. Karen Liu
Data-guided Model Predictive Control Based on Smoothed Contact Dynamics
Daseong Han, Haegwang Eom, Junyong Noh, and Joseph S. Shin (formerly Sung Yong Shin)
Browse
Recent Submissions
Item EUROGRAPHICS 2016: CGF 35-2 Frontmatter(The Eurographics Association and John Wiley & Sons Ltd., 2016) Joaquim Jorge; Ming Lin;Item Fast and Robust Inversion-Free Shape Manipulation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Liu, Tiantian; Gao, Ming; Zhu, Lifeng; Sifakis, Eftychios; Kavan, Ladislav; Joaquim Jorge and Ming LinWe present a shape manipulation technique capable of producing deformations of 2D and 3D meshes, guaranteeing that no elements will be inverted. We achieve this by augmenting the quadratic ex-rotated elastic energy with additional convex terms that penalize the presence of inverted elements. Using a schedule of increasing penalty coefficients, we efficiently and robustly converge to an inversion free state by solving a sequence of unconstrained convex minimization problems. This process can be interpreted as a special purpose Semi-Definite Programming (SDP) solver. We demonstrate that our method outperforms solvers used in previous work, including commercial-grade SDP software (MOSEK). As an additional benefit, our method also converges to the solution via a more intuitive path, which can be used for quick preview. We demonstrate the efficacy of our scheme in a number of 2D and 3D shapes undergoing moderate to drastic deformation.Item Building Construction Sets by Tiling Grammar Simplification(The Eurographics Association and John Wiley & Sons Ltd., 2016) Kalojanov, Javor; Wand, Michael; Slusallek, Philipp; Joaquim Jorge and Ming LinThis paper poses the problem of fabricating physical construction sets from example geometry: A construction set provides a small number of different types of building blocks from which the example model as well as many similar variants can be reassembled. This process is formalized by tiling grammars. Our core contribution is an approach for simplifying tiling grammars such that we obtain physically manufacturable building blocks of controllable granularity while retaining variability, i.e., the ability to construct many different, related shapes. Simplification is performed by sequences of two types of elementary operations: non-local joint edge collapses in the tile graphs reduce the granularity of the decomposition and approximate replacement operations reduce redundancy. We evaluate our method on abstract graph grammars in addition to computing several physical construction sets, which are manufactured using a commodity 3D printer.Item Structure-adaptive Shape Editing for Man-made Objects(The Eurographics Association and John Wiley & Sons Ltd., 2016) Fu, Qiang; Chen, Xiaowu; Su, Xiaoyu; Li, Jia; Fu, Hongbo; Joaquim Jorge and Ming LinOne of the challenging problems for shape editing is to adapt shapes with diversified structures for various editing needs. In this paper we introduce a shape editing approach that automatically adapts the structure of a shape being edited with respect to user inputs. Given a category of shapes, our approach first classifies them into groups based on the constituent parts. The group-sensitive priors, including both inter-group and intra-group priors, are then learned through statistical structure analysis and multivariate regression. By using these priors, the inherent characteristics and typical variations of shape structures can be well captured. Based on such group-sensitive priors, we propose a framework for real-time shape editing, which adapts the structure of shape to continuous user editing operations. Experimental results show that the proposed approach is capable of both structure-preserving and structure-varying shape editing.Item SMARTCANVAS: Context-inferred Interpretation of Sketches for Preparatory Design Studies(The Eurographics Association and John Wiley & Sons Ltd., 2016) Zheng, Youyi; Liu, Han; Dorsey, Julie; Mitra, Niloy J.; Joaquim Jorge and Ming LinIn early or preparatory design stages, an architect or designer sketches out rough ideas, not only about the object or structure being considered, but its relation to its spatial context. This is an iterative process, where the sketches are not only the primary means for testing and refining ideas, but also for communicating among a design team and to clients. Hence, sketching is the preferred media for artists and designers during the early stages of design, albeit with a major drawback: sketches are 2D and effects such as view perturbations or object movement are not supported, thereby inhibiting the design process. We present an interactive system that allows for the creation of a 3D abstraction of a designed space, built primarily by sketching in 2D within the context of an anchoring design or photograph. The system is progressive in the sense that the interpretations are refined as the user continues sketching. As a key technical enabler, we reformulate the sketch interpretation process as a selection optimization from a set of context-generated canvas planes in order to retrieve a regular arrangement of planes. We demonstrate our system (available at http:/geometry.cs.ucl.ac.uk/projects/2016/smartcanvas/) with a wide range of sketches and design studies.Item Buoyancy Optimization for Computational Fabrication(The Eurographics Association and John Wiley & Sons Ltd., 2016) Wang, Lingfeng; Whiting, Emily; Joaquim Jorge and Ming LinThis paper introduces a design and fabrication pipeline for creating floating forms. Our method optimizes for buoyant equilibrium and stability of complex 3D shapes, applying a voxel-carving technique to control the mass distribution. The resulting objects achieve a desired floating pose defined by a user-specified waterline height and orientation. In order to enlarge the feasible design space, we explore novel ways to load the interior of a design using prefabricated components and casting techniques. 3D printing is employed for high-precision fabrication. For larger scale designs we introduce a method for stacking lasercut planar pieces to create 3D objects in a quick and economic manner. We demonstrate fabricated designs of complex shape in a variety of floating poses.Item Improved Surface Quality in 3D Printing by Optimizing the Printing Direction(The Eurographics Association and John Wiley & Sons Ltd., 2016) Wang, Weiming; Zanni, Cédric; Kobbelt, Leif; Joaquim Jorge and Ming LinWe present a pipeline of algorithms that decomposes a given polygon model into parts such that each part can be 3D printed with high (outer) surface quality. For this we exploit the fact that most 3D printing technologies have an anisotropic resolution and hence the surface smoothness varies significantly with the orientation of the surface. Our pipeline starts by segmenting the input surface into patches such that their normals can be aligned perpendicularly to the printing direction. A 3D Voronoi diagram is computed such that the intersections of the Voronoi cells with the surface approximate these surface patches. The intersections of the Voronoi cells with the input model's volume then provide an initial decomposition. We further present an algorithm to compute an assembly order for the parts and generate connectors between them. A post processing step further optimizes the seams between segments to improve the visual quality. We run our pipeline on a wide range of 3D models and experimentally evaluate the obtained improvements in terms of numerical, visual, and haptic quality.Item Generalized Diffusion Curves: An Improved Vector Representation for Smooth-Shaded Images(The Eurographics Association and John Wiley & Sons Ltd., 2016) Jeschke, Stefan; Joaquim Jorge and Ming LinThis paper generalizes the well-known Diffusion Curves Images (DCI), which are composed of a set of Bezier curves with colors specified on either side. These colors are diffused as Laplace functions over the image domain, which results in smooth color gradients interrupted by the Bezier curves. Our new formulation allows for more color control away from the boundary, providing a similar expressive power as recent Bilaplace image models without introducing associated issues and computational costs. The new model is based on a special Laplace function blending and a new edge blur formulation. We demonstrate that given some user-defined boundary curves over an input raster image, fitting colors and edge blur from the image to the new model and subsequent editing and animation is equally convenient as with DCIs. Numerous examples and comparisons to DCIs are presented.Item Generalized As-Similar-As-Possible Warping with Applications in Digital Photography(The Eurographics Association and John Wiley & Sons Ltd., 2016) Chen, Renjie; Gotsman, Craig; Joaquim Jorge and Ming LinDiscrete conformal mappings of planar triangle meshes, also known as the As-Similar-As-Possible (ASAP) mapping, involve the minimization of a quadratic energy function, thus are very easy to generate and are popular in image warping scenarios. We generalize this classical mapping to the case of quad meshes, taking into account the mapping of the interior of the quad, and analyze in detail the most common case - the unit grid mesh. We show that the generalization, when combined with barycentric coordinate mappings between the source and target polygons, spawns an entire family of new mappings governed by quadratic energy functions, which allow to control quite precisely various effects of the mapping. This approach is quite general and applies also to arbitrary planar polygon meshes. As an application of generalized ASAP mappings of the unit grid mesh, we demonstrate how they can be used to warp digital photographs to achieve a variety of effects. One such effect is modifying the perspective of the camera that took a given photograph (without moving the camera). A related, but more challenging, effect is re-photography - warping a contemporary photograph in order to reproduce the camera view present in a vintage photograph of the same scene - taken many years before with a different camera from a different viewpoint. We apply the generalized ASAP mapping to these images, discretized to a unit grid. Using a quad mesh (as opposed to a triangle mesh) permits biasing towards affine maps of the unit squares. This allows the introduction of an As-Affine-As-Possible (AAAP) mapping for a good approximation of the homographies present in these warps, achieving quite accurate results. We demonstrate the advantages of the AAAP mapping on a variety of synthetic and real-world examples.Item Automatic Portrait Segmentation for Image Stylization(The Eurographics Association and John Wiley & Sons Ltd., 2016) Shen, Xiaoyong; Hertzmann, Aaron; Jia, Jiaya; Paris, Sylvain; Price, Brian; Shechtman, Eli; Sachs, Ian; Joaquim Jorge and Ming LinPortraiture is a major art form in both photography and painting. In most instances, artists seek to make the subject stand out from its surrounding, for instance, by making it brighter or sharper. In the digital world, similar effects can be achieved by processing a portrait image with photographic or painterly filters that adapt to the semantics of the image. While many successful user-guided methods exist to delineate the subject, fully automatic techniques are lacking and yield unsatisfactory results. Our paper first addresses this problem by introducing a new automatic segmentation algorithm dedicated to portraits. We then build upon this result and describe several portrait filters that exploit our automatic segmentation algorithm to generate high-quality portraits.Item Motion Grammars for Character Animation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Hyun, Kyunglyul; Lee, Kyungho; Lee, Jehee; Joaquim Jorge and Ming LinThe behavioral structure of human movements is imposed by multiple sources, such as rules, regulations, choreography, habits, and emotion. Our goal is to identify the behavioral structure in a specific application domain and create a novel sequence of movements that abide by structure-building rules. To do so, we exploit the ideas from formal language, such as rewriting rules and grammar parsing, and adapted those ideas to synthesize the three-dimensional animation of multiple characters. The structured motion synthesis using motion grammars is formulated in two layers. The upper layer is a symbolic description that relates the semantics of each individual's movements and the interaction among them. The lower layer provides spatial and temporal contexts to the animation. Our multi-level MCMC (Markov Chain Monte Carlo) algorithm deals with the syntax, semantics, and spatiotemporal context of human motion to produce highly-structured, animated scenes. The power and effectiveness of motion grammars are demonstrated in animating basketball games from drawings on a tactic board. Our system allows the user to position players and draw out tactical plans, which are animated automatically in virtual environments with three-dimensional, full-body characters.Item Animation Setup Transfer for 3D Characters(The Eurographics Association and John Wiley & Sons Ltd., 2016) Avril, Quentin; Ghafourzadeh, Donya; Ramachandran, Srinivasan; Fallahdoust, Sahel; Ribet, Sarah; Dionne, Olivier; Lasa, Martin de; Paquette, Eric; Joaquim Jorge and Ming LinWe present a general method for transferring skeletons and skinning weights between characters with distinct mesh topologies. Our pipeline takes as inputs a source character rig (consisting of a mesh, a transformation hierarchy of joints, and skinning weights) and a target character mesh. From these inputs, we compute joint locations and orientations that embed the source skeleton in the target mesh, as well as skinning weights to bind the target geometry to the new skeleton. Our method consists of two key steps. We first compute the geometric correspondence between source and target meshes using a semi-automatic method relying on a set of markers. The resulting geometric correspondence is then used to formulate attribute transfer as an energy minimization and filtering problem. We demonstrate our approach on a variety of source and target bipedal characters, varying in mesh topology and morphology. Several examples demonstrate that the target characters behave well when animated with either forward or inverse kinematics. Via these examples, we show that our method preserves subtle artistic variations; spatial relationships between geometry and joints, as well as skinning weight details, are accurately maintained. Our proposed pipeline opens up many exciting possibilities to quickly animate novel characters by reusing existing production assets.Item Character Contact Re-positioning Under Large Environment Deformation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Tonneau, Steve; Al-Ashqar, Rami Ali; Pettré, Julien; Komura, Taku; Mansard, Nicolas; Joaquim Jorge and Ming LinCharacter animation based on motion capture provides intrinsically plausible results, but lacks the flexibility of procedural methods. Motion editing methods partially address this limitation by adapting the animation to small deformations of the environment.We extend one such method, the so-called relationship descriptors, to tackle the issue of motion editing under large environment deformations. Large deformations often result in joint limits violation, loss of balance, or collisions. Our method handles these situations by automatically detecting and re-positioning invalidated contacts. The new contact configurations are chosen to preserve the mechanical properties of the original contacts in order to provide plausible support phases. When it is not possible to find an equivalent contact, a procedural animation is generated and blended with the original motion. Thanks to an optimization scheme, the resulting motions are continuous and preserve the style of the reference motions. The method is fully interactive and enables the motion to be adapted on-line even in case of large changes of the environment. We demonstrate our method on several challenging scenarios, proving its immediate application to 3D animation softwares and video games.Item An Objective Deghosting Quality Metric for HDR Images(The Eurographics Association and John Wiley & Sons Ltd., 2016) Tursun, Okan Tarhan; Akyüz, Ahmet Oğuz; Erdem, Aykut; Erdem, Erkut; Joaquim Jorge and Ming LinReconstructing high dynamic range (HDR) images of a complex scene involving moving objects and dynamic backgrounds is prone to artifacts. A large number of methods have been proposed that attempt to alleviate these artifacts, known as HDR deghosting algorithms. Currently, the quality of these algorithms are judged by subjective evaluations, which are tedious to conduct and get quickly outdated as new algorithms are proposed on a rapid basis. In this paper, we propose an objective metric which aims to simplify this process. Our metric takes a stack of input exposures and the deghosting result and produces a set of artifact maps for different types of artifacts. These artifact maps can be combined to yield a single quality score. We performed a subjective experiment involving 52 subjects and 16 different scenes to validate the agreement of our quality scores with subjective judgements and observed a concordance of almost 80%. Our metric also enables a novel application that we call as hybrid deghosting, in which the output of different deghosting algorithms are combined to obtain a superior deghosting result.Item Convolutional Sparse Coding for High Dynamic Range Imaging(The Eurographics Association and John Wiley & Sons Ltd., 2016) Serrano, Ana; Heide, Felix; Gutierrez, Diego; Wetzstein, Gordon; Masia, Belen; Joaquim Jorge and Ming LinCurrent HDR acquisition techniques are based on either (i) fusing multibracketed, low dynamic range (LDR) images, (ii) modifying existing hardware and capturing different exposures simultaneously with multiple sensors, or (iii) reconstructing a single image with spatially-varying pixel exposures. In this paper, we propose a novel algorithm to recover high-quality HDRI images from a single, coded exposure. The proposed reconstruction method builds on recently-introduced ideas of convolutional sparse coding (CSC); this paper demonstrates how to make CSC practical for HDR imaging. We demonstrate that the proposed algorithm achieves higher-quality reconstructions than alternative methods, we evaluate optical coding schemes, analyze algorithmic parameters, and build a prototype coded HDR camera that demonstrates the utility of convolutional sparse HDRI coding with a custom hardware platform.Item Large Scale Terrain Generation from Tectonic Uplift and Fluvial Erosion(The Eurographics Association and John Wiley & Sons Ltd., 2016) Cordonnier, Guillaume; Braun, Jean; Cani, Marie-Paule; Benes, Bedrich; Galin, Éric; Peytavie, Adrien; Guérin, Éric; Joaquim Jorge and Ming LinAt large scale, landscapes result from the combination of two major processes: tectonics which generate the main relief through crust uplift, and weather which accounts for erosion. This paper presents the first method in computer graphics that combines uplift and hydraulic erosion to generate visually plausible terrains. Given a user-painted uplift map, we generate a stream graph over the entire domain embedding elevation information and stream flow. Our approach relies on the stream power equation introduced in geology for hydraulic erosion. By combining crust uplift and stream power erosion we generate large realistic terrains at a low computational cost. Finally, we convert this graph into a digital elevation model by blending landform feature kernels whose parameters are derived from the information in the graph. Our method gives high-level control over the large scale dendritic structures of the resulting river networks, watersheds, and mountains ridges.Item Sparse Representation of Terrains for Procedural Modeling(The Eurographics Association and John Wiley & Sons Ltd., 2016) Guérin, Eric; Digne, Julie; Galin, Eric; Peytavie, Adrien; Joaquim Jorge and Ming LinIn this paper, we present a simple and efficient method to represent terrains as elevation functions built from linear combinations of landform features (atoms). These features can be extracted either from real world data-sets or procedural primitives, or from any combination of multiple terrain models. Our approach consists in representing the elevation function as a sparse combination of primitives, a concept which we call Sparse Construction Tree, which blends the different landform features stored in a dictionary. The sparse representation allows us to represent complex terrains using combinations of atoms from a small dictionary, yielding a powerful and compact terrain representation and synthesis tool. Moreover, we present a method for automatically learning the dictionary and generating the Sparse Construction Tree model. We demonstrate the efficiency of our method in several applications: inverse procedural modeling of terrains, terrain amplification and synthesis from a coarse sketch.Item DeepProp: Extracting Deep Features from a Single Image for Edit Propagation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Endo, Yuki; Iizuka, Satoshi; Kanamori, Yoshihiro; Mitani, Jun; Joaquim Jorge and Ming LinEdit propagation is a technique that can propagate various image edits (e.g., colorization and recoloring) performed via user strokes to the entire image based on similarity of image features. In most previous work, users must manually determine the importance of each image feature (e.g., color, coordinates, and textures) in accordance with their needs and target images. We focus on representation learning that automatically learns feature representations only from user strokes in a single image instead of tuning existing features manually. To this end, this paper proposes an edit propagation method using a deep neural network (DNN). Our DNN, which consists of several layers such as convolutional layers and a feature combiner, extracts strokeadapted visual features and spatial features, and then adjusts the importance of them. We also develop a learning algorithm for our DNN that does not suffer from the vanishing gradient problem, and hence avoids falling into undesirable locally optimal solutions. We demonstrate that edit propagation with deep features, without manual feature tuning, can achieve better results than previous work.Item Smooth Image Sequences for Data-driven Morphing(The Eurographics Association and John Wiley & Sons Ltd., 2016) Averbuch-Elor, Hadar; Cohen-Or, Daniel; Kopf, Johannes; Joaquim Jorge and Ming LinSmoothness is a quality that feels aesthetic and pleasing to the human eye. We present an algorithm for finding ''as-smoothas- possible'' sequences in image collections. In contrast to previous work, our method does not assume that the images show a common 3D scene, but instead may depict different object instances with varying deformations, and significant variation in lighting, texture, and color appearance. Our algorithm does not rely on a notion of camera pose, view direction, or 3D representation of an underlying scene, but instead directly optimizes the smoothness of the apparent motion of local point matches among the collection images. We increase the smoothness of our sequences by performing a global similarity transform alignment, as well as localized geometric wobble reduction and appearance stabilization. Our technique gives rise to a new kind of image morphing algorithm, in which the in-between motion is derived in a data-driven manner from a smooth sequence of real images without any user intervention. This new type of morph can go far beyond the ability of traditional techniques. We also demonstrate that our smooth sequences allow exploring large image collections in a stable manner.Item Boundary Detection in Particle-based Fluids(The Eurographics Association and John Wiley & Sons Ltd., 2016) Sandim, Marcos; Cedrim, Douglas; Nonato, Luis Gustavo; Pagliosa, Paulo; Paiva, Afonso; Joaquim Jorge and Ming LinThis paper presents a novel method to detect free-surfaces on particle-based volume representation. In contrast to most particlebased free-surface detection methods, which perform the surface identification based on physical and geometrical properties derived from the underlying fluid flow simulation, the proposed approach only demands the spatial location of the particles to properly recognize surface particles, avoiding even the use of kernels. Boundary particles are identified through a Hidden Point Removal (HPR) operator used for visibility test. Our method is very simple, fast, easy to implement and robust to changes in the distribution of particles, even when facing large deformation of the free-surface. A set of comparisons against state-of-the-art boundary detection methods show the effectiveness of our approach. The good performance of our method is also attested in the context of fluid flow simulation involving free-surface, mainly when using level-sets for rendering purposes.Item Narrow Band FLIP for Liquid Simulations(The Eurographics Association and John Wiley & Sons Ltd., 2016) Ferstl, Florian; Ando, Ryoichi; Wojtan, Chris; Westermann, Rüdiger; Thuerey, Nils; Joaquim Jorge and Ming LinThe Fluid Implicit Particle method (FLIP) for liquid simulations uses particles to reduce numerical dissipation and provide important visual cues for events like complex splashes and small-scale features near the liquid surface. Unfortunately, FLIP simulations can be computationally expensive, because they require a dense sampling of particles to fill the entire liquid volume. Furthermore, the vast majority of these FLIP particles contribute nothing to the fluid's visual appearance, especially for larger volumes of liquid. We present a method that only uses FLIP particles within a narrow band of the liquid surface, while efficiently representing the remaining inner volume on a regular grid. We show that a naïve realization of this idea introduces unstable and uncontrollable energy fluctuations, and we propose a novel coupling scheme between FLIP particles and regular grid which overcomes this problem. Our method drastically reduces the particle count and simulation times while yielding results that are nearly indistinguishable from regular FLIP simulations. Our approach is easy to integrate into any existing FLIP implementation.Item A Practical Method for High-Resolution Embedded Liquid Surfaces(The Eurographics Association and John Wiley & Sons Ltd., 2016) Goldade, Ryan; Batty, Christopher; Wojtan, Chris; Joaquim Jorge and Ming LinCombining high-resolution level set surface tracking with lower resolution physics is an inexpensive method for achieving highly detailed liquid animations. Unfortunately, the inherent resolution mismatch introduces several types of disturbing visual artifacts. We identify the primary sources of these artifacts and present simple, efficient, and practical solutions to address them. First, we propose an unconditionally stable filtering method that selectively removes sub-grid surface artifacts not seen by the fluid physics, while preserving fine detail in dynamic splashing regions. It provides comparable results to recent error-correction techniques at lower cost, without substepping, and with better scaling behavior. Second, we show how a modified narrow-band scheme can ensure accurate free surface boundary conditions in the presence of large resolution mismatches. Our scheme preserves the efficiency of the narrow-band methodology, while eliminating objectionable stairstep artifacts observed in prior work. Third, we demonstrate that the use of linear interpolation of velocity during advection of the high-resolution level set surface is responsible for visible grid-aligned kinks; we therefore advocate higher-order velocity interpolation, and show that it dramatically reduces this artifact. While these three contributions are orthogonal, our results demonstrate that taken together they efficiently address the dominant sources of visual artifacts arising with high-resolution embedded liquid surfaces; the proposed approach offers improved visual quality, a straightforward implementation, and substantially greater scalability than competing methods.Item Stylized Caustics: Progressive Rendering of Animated Caustics(The Eurographics Association and John Wiley & Sons Ltd., 2016) Günther, Tobias; Rohmer, Kai; Rössl, Christian; Grosch, Thorsten; Theisel, Holger; Joaquim Jorge and Ming LinIn recent years, much work was devoted to the design of light editing methods such as relighting and light path editing. So far, little work addressed the target-based manipulation and animation of caustics, for instance to a differently-shaped caustic, text or an image. The aim of this work is the animation of caustics by blending towards a given target irradiance distribution. This enables an artist to coherently change appearance and style of caustics, e.g., for marketing applications and visual effects. Generating a smooth animation is nontrivial, as photon density and caustic structure may change significantly. Our method is based on the efficient solution of a discrete assignment problem that incorporates constraints appropriate to make intermediate blends plausibly resemble caustics. The algorithm generates temporally coherent results that are rendered with stochastic progressive photon mapping. We demonstrate our system in a number of scenes and show blends as well as a key frame animation.Item Multi-Resolution Meshes for Feature-Aware Hardware Tessellation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Lambert, Thibaud; Bénard, Pierre; Guennebaud, Gaël; Joaquim Jorge and Ming LinHardware tessellation is de facto the preferred mechanism to adaptively control mesh resolution with maximal performances. However, owing to its fixed and uniform pattern, leveraging tessellation for feature-aware LOD rendering remains a challenging problem. We relax this fundamental constraint by introducing a new spatial and temporal blending mechanism of tessellation levels, which is built on top of a novel hierarchical representation of multi-resolution meshes. This mechanism allows to finely control topological changes so that vertices can be removed or added at the most appropriate location to preserve geometric features in a continuous and artifact-free manner. We then show how to extend edge-collapse based decimation methods to build feature-aware multi-resolution meshes that match the tessellation patterns. Our approach is fully compatible with current hardware tessellators and only adds a small overhead on memory consumption and tessellation cost.Item Regularizing Image Reconstruction for Gradient-Domain Rendering with Feature Patches(The Eurographics Association and John Wiley & Sons Ltd., 2016) Manzi, Marco; Vicini, Delio; Zwicker, Matthias; Joaquim Jorge and Ming LinWe present a novel algorithm to reconstruct high-quality images from sampled pixels and gradients in gradient-domain rendering. Our approach extends screened Poisson reconstruction by adding additional regularization constraints. Our key idea is to exploit local patches in feature images, which contain per-pixels normals, textures, position, etc., to formulate these constraints. We describe a GPU implementation of our approach that runs on the order of seconds on megapixel images. We demonstrate a significant improvement in image quality over screened Poisson reconstruction under the L1 norm. Because we adapt the regularization constraints to the noise level in the input, our algorithm is consistent and converges to the ground truth.Item A Practical and Controllable Hair and Fur Model for Production Path Tracing(The Eurographics Association and John Wiley & Sons Ltd., 2016) Chiang, Matt Jen-Yuan; Bitterli, Benedikt; Tappan, Chuck; Burley, Brent; Joaquim Jorge and Ming LinWe present an energy-conserving fiber shading model for hair and fur that is efficient enough for path tracing. Our model adopts a near-field formulation to avoid the expensive integral across the fiber, accounts for all high order internal reflection events with a single lobe, and proposes a novel, closed-form distribution for azimuthal roughness based on the logistic distribution. Additionally, we derive, through simulation, a parameterization that relates intuitive user controls such as multiple-scattering albedo and isotropic cylinder roughness to the underlying physical parameters.Item SAH Guided Spatial Split Partitioning for Fast BVH Construction(The Eurographics Association and John Wiley & Sons Ltd., 2016) Ganestam, Per; Doggett, Michael; Joaquim Jorge and Ming LinWe present a new SAH guided approach to subdividing triangles as the scene is coarsely partitioned into smaller sets of spatially coherent triangles. Our triangle split approach is integrated into the partitioning stage of a fast BVH construction algorithm, but may as well be used as a stand alone pre-split pass. Our algorithm significantly reduces the number of split triangles compared to previous methods, while at the same time improving ray tracing performance compared to competing fast BVH construction techniques. We compare performance on Intel's Embree ray tracer and show that BVH construction with our splitting algorithm is always faster than Embree's pre-split construction algorithm. We also show that our algorithm builds significantly improved quality trees that deliver higher ray tracing performance. Our algorithm is implemented into Embree's open source ray tracing framework, and the source code will be released late 2015.Item Geometric Flows of Curves in Shape Space for Processing Motion of Deformable Objects(The Eurographics Association and John Wiley & Sons Ltd., 2016) Brandt, Christopher; Tycowicz, Christoph von; Hildebrandt, Klaus; Joaquim Jorge and Ming LinWe introduce techniques for the processing of motion and animations of non-rigid shapes. The idea is to regard animations of deformable objects as curves in shape space. Then, we use the geometric structure on shape space to transfer concepts from curve processing in Rn to the processing of motion of non-rigid shapes. Following this principle, we introduce a discrete geometric flow for curves in shape space. The flow iteratively replaces every shape with a weighted average shape of a local neighborhood and thereby globally decreases an energy whose minimizers are discrete geodesics in shape space. Based on the flow, we devise a novel smoothing filter for motions and animations of deformable shapes. By shortening the length in shape space of an animation, it systematically regularizes the deformations between consecutive frames of the animation. The scheme can be used for smoothing and noise removal, e.g., for reducing jittering artifacts in motion capture data. We introduce a reduced-order method for the computation of the flow. In addition to being efficient for the smoothing of curves, it is a novel scheme for computing geodesics in shape space. We use the scheme to construct non-linear ''Bézier curves'' by executing de Casteljau's algorithm in shape space.Item A Multi-sided Bézier Patch with a Simple Control Structure(The Eurographics Association and John Wiley & Sons Ltd., 2016) Várady, Tamás; Salvi, Péter; Karikó, György; Joaquim Jorge and Ming LinA new n-sided surface scheme is presented, that generalizes tensor product Bézier patches. Boundaries and corresponding crossderivatives are specified as conventional Bézier surfaces of arbitrary degrees. The surface is defined over a convex polygonal domain; local coordinates are computed from generalized barycentric coordinates; control points are multiplied by weighted, biparametric Bernstein functions. A method for interpolating a middle point is also presented. This Generalized Bézier (GB) patch is based on a new displacement scheme that builds up multi-sided patches as a combination of a base patch, n displacement patches and an interior patch; this is considered to be an alternative to the Boolean sum concept. The input ribbons may have different degrees, but the final patch representation has a uniform degree. Interior control points- other than those specified by the user-are placed automatically by a special degree elevation algorithm. GB patches connect to adjacent Bézier surfaces with G1 continuity. The control structure is simple and intuitive; the number of control points is proportional to those of quadrilateral control grids. The scheme is introduced through simple examples; suggestions for future work are also discussed.Item Compressed Multiresolution Hierarchies for High-Quality Precomputed Shadows(The Eurographics Association and John Wiley & Sons Ltd., 2016) Scandolo, Leonardo; Bauszat, Pablo; Eisemann, Elmar; Joaquim Jorge and Ming LinThe quality of shadow mapping is traditionally limited by texture resolution. We present a novel lossless compression scheme for high-resolution shadow maps based on precomputed multiresolution hierarchies. Traditional multiresolution trees can compactly represent homogeneous regions of shadow maps at coarser levels, but require many nodes for fine details. By conservatively adapting the depth map, we can significantly reduce the tree complexity. Our proposed method offers high compression rates, avoids quantization errors, exploits coherency along all data dimensions, and is well-suited for GPU architectures. Our approach can be applied for coherent shadow maps as well, enabling several applications, including high-quality soft shadows and dynamic lights moving on fixed-trajectories.Item Adapting Feature Curve Networks to a Prescribed Scale(The Eurographics Association and John Wiley & Sons Ltd., 2016) Gehre, Anne; Lim, Isaak; Kobbelt, Leif; Joaquim Jorge and Ming LinFeature curves on surface meshes are usually defined solely based on local shape properties such as dihedral angles and principal curvatures. From the application perspective, however, the meaningfulness of a network of feature curves also depends on a global scale parameter that takes the distance between feature curves into account, i.e., on a coarse scale, nearby feature curves should be merged or suppressed if the surface region between them is not representable at the given scale/resolution. In this paper, we propose a computational approach to the intuitive notion of scale conforming feature curve networks where the density of feature curves on the surface adapts to a global scale parameter. We present a constrained global optimization algorithm that computes scale conforming feature curve networks by eliminating curve segments that represent surface features, which are not compatible to the prescribed scale. To demonstrate the usefulness of our approach we apply isotropic and anisotropic remeshing schemes that take our feature curve networks as input. For a number of example meshes, we thus generate high quality shape approximations at various levels of detail.Item BlendForces: A Dynamic Framework for Facial Animation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Barrielle, Vincent; Stoiber, Nicolas; Cagniart, Cédric; Joaquim Jorge and Ming LinIn this paper we present a new paradigm for the generation and retargeting of facial animation. Like a vast majority of the approaches that have adressed these topics, our formalism is built on blendshapes. However, where prior works have generally encoded facial geometry using a low dimensional basis of these blendshapes, we propose to encode facial dynamics by looking at blendshapes as a basis of forces rather than a basis of shapes. We develop this idea into a dynamic model that naturally combines the blendshapes paradigm with physics-based techniques for the simulation of deforming meshes. Because it escapes the linear span of the shape basis through time-integration and physics-inspired simulation, this approach has a wider expres- sive range than previous blendshape-based methods. Its inherent physically-based formulation also enables the simulation of more advanced physical interactions, such as collision responses on lip contacts.Item Near-Instant Capture of High-Resolution Facial Geometry and Reflectance(The Eurographics Association and John Wiley & Sons Ltd., 2016) Fyffe, Graham; Graham, Paul; Tunwattanapong, Borom; Ghosh, Abhijeet; Debevec, Paul; Joaquim Jorge and Ming LinWe present a near-instant method for acquiring facial geometry and reflectance using a set of commodity DSLR cameras and flashes. Our setup consists of twenty-four cameras and six flashes which are fired in rapid succession with subsets of the cameras. Each camera records only a single photograph and the total capture time is less than the 67ms blink reflex. The cameras and flashes are specially arranged to produce an even distribution of specular highlights on the face. We employ this set of acquired images to estimate diffuse color, specular intensity, specular exponent, and surface orientation at each point on the face. We further refine the facial base geometry obtained from multi-view stereo using estimated diffuse and specular photometric information. This allows final submillimeter surface mesostructure detail to be obtained via shape-from-specularity. The final system uses commodity components and produces models suitable for authoring high-quality digital human characters.Item Learning 3D Deformation of Animals from 2D Images(The Eurographics Association and John Wiley & Sons Ltd., 2016) Kanazawa, Angjoo; Kovalsky, Shahar; Basri, Ronen; Jacobs, David; Joaquim Jorge and Ming LinUnderstanding how an animal can deform and articulate is essential for a realistic modification of its 3D model. In this paper, we show that such information can be learned from user-clicked 2D images and a template 3D model of the target animal. We present a volumetric deformation framework that produces a set of new 3D models by deforming a template 3D model according to a set of user-clicked images. Our framework is based on a novel locally-bounded deformation energy, where every local region has its own stiffness value that bounds how much distortion is allowed at that location. We jointly learn the local stiffness bounds as we deform the template 3D mesh to match each user-clicked image. We show that this seemingly complex task can be solved as a sequence of convex optimization problems. We demonstrate the effectiveness of our approach on cats and horses, which are highly deformable and articulated animals. Our framework produces new 3D models of animals that are significantly more plausible than methods without learned stiffness.Item Effect of Low-level Visual Details in Perception of Deformation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Han, Donghui; Keyser, John; Joaquim Jorge and Ming LinWe quantitatively measure how different low-level visual details can influence people's perceived stiffness of a deformable sphere under physically based simulation. The result can be used to create a metric for artists in designing textures to enhance or reduce the stiffness perceived by a viewer. We use a checkerboard texture to render the simulation of a free falling sphere that collides with the ground and bounces up. We vary the spatial frequency and contrast of the checkerboard pattern according to results seen in a previous study on the Spatial- Temporal Contrast Sensitivity Function (CSF).We find that checkerboard pattern with certain combinations of spatial frequency and contrast can reduce the perceived stiffness. We also add a high contrast checkerboard background to study how complex backgrounds can influence the effect of low-level details in textures of foreground objects. Our study shows that the effect of low-level visual details in foreground objects observed previously disappears in this situation. This indicates the importance of background, even if it is static.Item Modeling and Estimation of Energy-Based Hyperelastic Objects(The Eurographics Association and John Wiley & Sons Ltd., 2016) Miguel, Eder; Miraut, David; Otaduy, Miguel A.; Joaquim Jorge and Ming LinIn this paper, we present a method to model hyperelasticity that is well suited for representing the nonlinearity of real-world objects, as well as for estimating it from deformation examples. Previous approaches suffer several limitations, such as lack of integrability of elastic forces, failure to enforce energy convexity, lack of robustness of parameter estimation, or difficulty to model cross-modal effects. Our method avoids these problems by relying on a general energy-based definition of elastic properties. The accuracy of the resulting elastic model is maximized by defining an additive model of separable energy terms, which allow progressive parameter estimation. In addition, our method supports efficient modeling of extreme nonlinearities thanks to energy-limiting constraints. We combine our energy-based model with an optimization method to estimate model parameters from force-deformation examples, and we show successful modeling of diverse deformable objects, including cloth, human finger skin, and internal human anatomy in a medical imaging application.Item Geometry and Attribute Compression for Voxel Scenes(The Eurographics Association and John Wiley & Sons Ltd., 2016) Dado, Bas; Kol, Timothy R.; Bauszat, Pablo; Thiery, Jean-Marc; Eisemann, Elmar; Joaquim Jorge and Ming LinVoxel-based approaches are today's standard to encode volume data. Recently, directed acyclic graphs (DAGs) were successfully used for compressing sparse voxel scenes as well, but they are restricted to a single bit of (geometry) information per voxel. We present a method to compress arbitrary data, such as colors, normals, or reflectance information. By decoupling geometry and voxel data via a novel mapping scheme, we are able to apply the DAG principle to encode the topology, while using a palette-based compression for the voxel attributes, leading to a drastic memory reduction. Our method outperforms existing state-of-the-art techniques and is well-suited for GPU architectures. We achieve real-time performance on commodity hardware for colored scenes with up to 17 hierarchical levels (a 128K3 voxel resolution), which are stored fully in core.Item VBTC: GPU-Friendly Variable Block Size Texture Encoding(The Eurographics Association and John Wiley & Sons Ltd., 2016) Krajcevski, Pavel; Golas, Abhinav; Ramani, Karthik; Shebanow, Michael; Manocha, Dinesh; Joaquim Jorge and Ming LinRecent advances in computer graphics have relied on high-quality textures in order to generate photorealistic real-time images. Texture compression standards meet these growing demands for data, but current texture compression schemes use fixed-rate methods where statically sized blocks of pixels are represented using the same numbers of bits irrespective of their data content. In order to account for the natural variation in detail, we present an alternative format that allows variable bit-rate texture compression with minimal changes to texturing hardware. Our proposed scheme uses one additional level of indirection to allow the variation of the block size across the same texture. This single change is exploited to both vary the amount of bits allocated to certain parts of the texture and to duplicate redundant texture information across multiple pixels. To minimize hardware changes, the method picks combinations of block sizes and compression methods from existing fixed-rate standards. With this approach, our method is able to demonstrate energy savings of up to 50%, as well as higher quality compressed textures over current state of the art techniques.Item Space-Time Co-Segmentation of Articulated Point Cloud Sequences(The Eurographics Association and John Wiley & Sons Ltd., 2016) Yuan, Qing; Li, Guiqing; Xu, Kai; Chen, Xudong; Huang, Hui; Joaquim Jorge and Ming LinConsistent segmentation is to the center of many applications based on dynamic geometric data. Directly segmenting a raw 3D point cloud sequence is a challenging task due to the low data quality and large inter-frame variation across the whole sequence. We propose a local-to-global approach to co-segment point cloud sequences of articulated objects into near-rigid moving parts. Our method starts from a per-frame point clustering, derived from a robust voting-based trajectory analysis. The local segments are then progressively propagated to the neighboring frames with a cut propagation operation, and further merged through all frames using a novel space-time segment grouping technqiue, leading to a globally consistent and compact segmentation of the entire articulated point cloud sequence. Such progressive propagating and merging, in both space and time dimensions, makes our co-segmentation algorithm especially robust in handling noise, occlusions and pose/view variations that are usually associated with raw scan data.Item Anisotropic Diffusion Descriptors(The Eurographics Association and John Wiley & Sons Ltd., 2016) Boscaini, Davide; Masci, Jonathan; Rodolà , Emanuele; Bronstein, Michael M.; Cremers, Daniel; Joaquim Jorge and Ming LinSpectral methods have recently gained popularity in many domains of computer graphics and geometry processing, especially shape processing, computation of shape descriptors, distances, and correspondence. Spectral geometric structures are intrinsic and thus invariant to isometric deformations, are efficiently computed, and can be constructed on shapes in different representations. A notable drawback of these constructions, however, is that they are isotropic, i.e., insensitive to direction. In this paper, we show how to construct direction-sensitive spectral feature descriptors using anisotropic diffusion on meshes and point clouds. The core of our construction are directed local kernels acting similarly to steerable filters, which are learned in a task-specific manner. Remarkably, while being intrinsic, our descriptors allow to disambiguate reflection symmetries. We show the application of anisotropic descriptors for problems of shape correspondence on meshes and point clouds, achieving results significantly better than state-of-the-art methods.Item General Projective Maps for Multidimensional Data Projection(The Eurographics Association and John Wiley & Sons Ltd., 2016) Lehmann, Dirk J.; Theisel, Holger; Joaquim Jorge and Ming LinTo project high-dimensional data to a 2D domain, there are two well-established classes of approaches: RadViz and Star Coordinates. Both are well-explored in terms of accuracy, completeness, distortions, and interaction issues. We present a generalization of both RadViz and Star Coordinates such that it unifies both approaches. We do so by considering the space of all projective projections. This gives additional degrees of freedom, which we use for three things: Firstly, we define a smooth transition between RadViz and Star Coordinates allowing the user to exploit the advantages of both approaches. Secondly, we define a data-dependent magic lens to explore the data. Thirdly, we optimize the new degrees of freedom to minimize distortion. We apply our approach to a number of high-dimensional benchmark datasets.Item Inertial Steady 2D Vector Field Topology(The Eurographics Association and John Wiley & Sons Ltd., 2016) Günther, Tobias; Theisel, Holger; Joaquim Jorge and Ming LinVector field topology is a powerful and matured tool for the study of the asymptotic behavior of tracer particles in steady flows. Yet, it does not capture the behavior of finite-sized particles, because they develop inertia and do not move tangential to the flow. In this paper, we use the fact that the trajectories of inertial particles can be described as tangent curves of a higher dimensional vector field. Using this, we conduct a full classification of the first-order critical points of this higher dimensional flow, and devise a method to their efficient extraction. Further, we interactively visualize the asymptotic behavior of finite-sized particles by a glyph visualization that encodes the outcome of any initial condition of the governing ODE, i.e., for a varying initial position and/or initial velocity. With this, we present a first approach to extend traditional vector field topology to the inertial case.Item Multisampling Compressive Video Spectroscopy(The Eurographics Association and John Wiley & Sons Ltd., 2016) Jeon, Daniel S.; Choi, Inchang; Kim, Min H.; Joaquim Jorge and Ming LinThe coded aperture snapshot spectral imaging (CASSI) architecture has been employed widely for capturing hyperspectral video. Despite allowing concurrent capture of hyperspectral video, spatial modulation in CASSI sacrifices image resolution significantly while reconstructing spectral projection via sparse sampling. Several multiview alternatives have been proposed to handle this low spatial resolution problem and improve measurement accuracy, for instance, by adding a translation stage for the coded aperture or changing the static coded aperture with a digital micromirror device for dynamic modulation. Stateof- the-art solutions enhance spatial resolution significantly but are incapable of capturing video using CASSI. In this paper, we present a novel compressive coded aperture imaging design that increases spatial resolution while capturing 4D hyperspectral video of dynamic scenes. We revise the traditional CASSI design to allow for multiple sampling of the randomness of spatial modulation in a single frame. We demonstrate that our compressive video spectroscopy approach yields enhanced spatial resolution and consistent measurements, compared with the traditional CASSI design.Item Seamless Video Stitching from Hand-held Camera Inputs(The Eurographics Association and John Wiley & Sons Ltd., 2016) Lin, Kaimo; Liu, Shuaicheng; Cheong, Loong-Fah; Zeng, Bing; Joaquim Jorge and Ming LinImages/videos captured by portable devices (e.g., cellphones, DV cameras) often have limited fields of view. Image stitching, also referred to as mosaics or panorama, can produce a wide angle image by compositing several photographs together. Although various methods have been developed for image stitching in recent years, few works address the video stitching problem. In this paper, we present the first system to stitch videos captured by hand-held cameras. We first recover the 3D camera paths and a sparse set of 3D scene points using CoSLAM system, and densely reconstruct the 3D scene in the overlapping regions. Then, we generate a smooth virtual camera path, which stays in the middle of the original paths. Finally, the stitched video is synthesized along the virtual path as if it was taken from this new trajectory. The warping required for the stitching is obtained by optimizing over both temporal stability and alignment quality, while leveraging on 3D information at our disposal. The experiments show that our method can produce high quality stitching results for various challenging scenarios.Item Interactive Videos: Plausible Video Editing using Sparse Structure Points(The Eurographics Association and John Wiley & Sons Ltd., 2016) Chang, Chia-Sheng; Chu, Hung-Kuo; Mitra, Niloy J.; Joaquim Jorge and Ming LinVideo remains the method of choice for capturing temporal events. However, without access to the underlying 3D scene models, it remains difficult to make object level edits in a single video or across multiple videos. While it may be possible to explicitly reconstruct the 3D geometries to facilitate these edits, such a workflow is cumbersome, expensive, and tedious. In this work, we present a much simpler workflow to create plausible editing and mixing of raw video footage using only sparse structure points (SSP) directly recovered from the raw sequences. First, we utilize user-scribbles to structure the point representations obtained using structure-from-motion on the input videos. The resultant structure points, even when noisy and sparse, are then used to enable various video edits in 3D, including view perturbation, keyframe animation, object duplication and transfer across videos, etc. Specifically, we describe how to synthesize object images from new views adopting a novel image-based rendering technique using the SSPs as proxy for the missing 3D scene information. We propose a structure-preserving image warping on multiple input frames adaptively selected from object video, followed by a spatio-temporally coherent image stitching to compose the final object image. Simple planar shadows and depth maps are synthesized for objects to generate plausible video sequence mimicking real-world interactions. We demonstrate our system on a variety of input videos to produce complex edits, which are otherwise difficult to achieve.Item Single Image Weathering via Exemplar Propagation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Iizuka, Satoshi; Endo, Yuki; Kanamori, Yoshihiro; Mitani, Jun; Joaquim Jorge and Ming LinThis paper presents an efficient approach for generating weathering effects with detailed appearance variations in a single image. Previous approaches merely change chroma or reflectance of weathered objects, which is not sufficient for materials with detailed shading and texture variations, such as growing moss and peeling plaster. Our method propagates such detailed features via seamless patch-based synthesis driven by weathering degree distribution. Unlike previous methods, the weathering degrees are calculated efficiently using Radial Basis Functions even for materials with wide color variations. We use graph cut-based optimization to identify the most weathered region as a ''weathering exemplar'', from which we sample weathering patches. We demonstrate our method enables us to generate various types of detailed weathering effects interactively.Item CAMA: Contact-Aware Matrix Assembly with Unified Collision Handling for GPU-based Cloth Simulation(The Eurographics Association and John Wiley & Sons Ltd., 2016) Tang, Min; Wang, Huamin; Tang, Le; Tong, Ruofeng; Manocha, Dinesh; Joaquim Jorge and Ming LinWe present a novel GPU-based approach to robustly and efficiently simulate high-resolution and complexly layered cloth. The key component of our formulation is a parallelized matrix assembly algorithm that can quickly build a large and sparse matrix in a compressed format and accurately solve linear systems on GPUs. We also present a fast and integrated solution for parallel collision handling, including collision detection and response computations, which utilizes spatio-temporal coherence. We combine these algorithms as part of a new cloth simulation pipeline that incorporates contact forces into implicit time integration for collision avoidance. The entire pipeline is implemented on GPUs, and we evaluate its performance on complex benchmarks consisting of 100 - 300K triangles. In practice, our system takes a few seconds to simulate one frame of a complex cloth scene, which represents significant speedups over prior CPU and GPU-based cloth simulation systems.Item Dexterous Manipulation of Cloth(The Eurographics Association and John Wiley & Sons Ltd., 2016) Bai, Yunfei; Yu, Wenhao; Liu, C. Karen; Joaquim Jorge and Ming LinThis paper introduces a new technique to synthesize dexterous manipulation of cloth. Given a simple description of the desired cloth motion, our algorithm computes appropriate joint torques for physically simulated hands, such that, via contact forces, the result of cloth simulation follows the desired motion. Instead of optimizing the hand control forces directly, we formulate an optimization problem that solves for the commanding forces from the hands to the cloth, which have more direct impact on the dynamic state of the hands and that of the cloth. The solution of the optimization provides commanding forces that achieve the desired cloth motion described by the user, while respecting the kinematic constraints of the hands. These commanding forces are then used to guide the joint torques of the hands. To balance between the effectiveness of control and computational costs, we formulate a model-predictive-control problem as a quadratic program at each time step. We demonstrate our technique on a set of cloth manipulation tasks in daily activities, including folding laundry, wringing a towel, and putting on a scarf.Item Data-guided Model Predictive Control Based on Smoothed Contact Dynamics(The Eurographics Association and John Wiley & Sons Ltd., 2016) Han, Daseong; Eom, Haegwang; Noh, Junyong; Shin, Joseph S. (formerly Sung Yong); Joaquim Jorge and Ming LinIn this paper, we propose an efficient data-guided method based on Model Predictive Control (MPC) to synthesize a full-body motion. Guided by a reference motion, our method repeatedly plans the full-body motion to produce an optimal control policy for predictive control while sliding the fixed-span window along the time axis. Based on this policy, the method computes the joint torques of a character at every time step. Together with contact forces and external perturbations if there are any, the joint torques are used to update the state of the character. Without including the contact forces in the control vector, our formulation of the trajectory optimization problem enables automatic adjustment of contact timings and positions for balancing in response to environmental changes and external perturbations. For efficiency, we adopt derivative-based trajectory optimization on top of state-of-the-art smoothed contact dynamics. Use of derivatives enables our method to run much faster than the existing sampling-based methods. In order to further accelerate the performance of MPC, we propose efficient numerical differentiation of the system dynamics of a full-body character based on two schemes: data reuse and data interpolation. The former scheme exploits data dependency to reuse physical quantities of the system dynamics at near-by time points. The latter scheme allows the use of derivatives at sparse sample points to interpolate those at other time points in the window. We further accelerate evaluation of the system dynamics by exploiting the sparsity of physical quantities such as Jacobian matrix resulting from the tree-like structure of the articulated body. Through experiments, we show that the proposed method efficiently can synthesize realistic motions such as locomotion, dancing, gymnastic motions, and martial arts at interactive rates using moderate computing resources.