34-Issue 7

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https://diglib.eg.org/handle/10.2312/13266

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4D Model Flow: Precomputed Appearance Alignment for Real-time 4D Video Interpolation
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Casas, Dan; Richardt, Christian; Collomosse, John; Theobalt, Christian; Hilton, Adrian; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We introduce the concept of 4D model flow for the precomputed alignment of dynamic surface appearance across 4D video sequences of different motions reconstructed from multi-view video. Precomputed 4D model flow allows the efficient parametrization of surface appearance from the captured videos, which enables efficient real-time rendering of interpolated 4D video sequences whilst accurately reproducing visual dynamics, even when using a coarse underlying geometry. We estimate the 4D model flow using an image-based approach that is guided by available geometry proxies. We propose a novel representation in surface texture space for efficient storage and online parametric interpolation of dynamic appearance. Our 4D model flow overcomes previous requirements for computationally expensive online optical flow computation for data-driven alignment of dynamic surface appearance by precomputing the appearance alignment. This leads to an efficient rendering technique that enables the online interpolation between 4D videos in real time, from arbitrary viewpoints and with visual quality comparable to the state of the art.
Brushables: Example-based Edge-aware Directional Texture Painting
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Lukáč, Michal; Fišer, Jakub; Asente, Paul; Lu, Jingwan; Shechtman, Eli; Sýkora, Daniel; Stam, Jos and Mitra, Niloy J. and Xu, Kun
In this paper we present Brushables-a novel approach to example-based painting that respects user-specified shapes at the global level and preserves textural details of the source image at the local level. We formulate the synthesis as a joint optimization problem that simultaneously synthesizes the interior and the boundaries of the region, transferring relevant content from the source to meaningful locations in the target. We also provide an intuitive interface to control both local and global direction of textural details in the synthesized image. A key advantage of our approach is that it enables a ''combing'' metaphor in which the user can incrementally modify the target direction field to achieve the desired look. Based on this, we implement an interactive texture painting tool capable of handling more complex textures than ever before, and demonstrate its versatility on difficult inputs including vegetation, textiles, hair and painting media.
Contrast-Enhanced Black and White Images
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Li, Hua; Mould, David; Stam, Jos and Mitra, Niloy J. and Xu, Kun
This paper investigates contrast enhancement as an approach to tone reduction, aiming to convert a photograph to black and white. Using a filter-based approach to strengthen contrast, we avoid making a hard decision about how to assign tones to segmented regions. Our method is inspired by sticks filtering, used to enhance medical images but not previously used in non-photorealistic rendering. We amplify contrast of pixels along the direction of greatest local difference from the mean, strengthening even weak features if they are most prominent. A final thresholding step converts the contrast-enhanced image to black and white. Local smoothing and contrast enhancement balances abstraction and structure preservation; the main advantage of our method is its faithful depiction of image detail. Our method can create a set of effects: line drawing, hatching, and black and white, all having superior details to previous black and white methods.
Data-driven Handwriting Synthesis in a Conjoined Manner
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Chen, Hsin-I; Lin, Tse-Ju; Jian, Xiao-Feng; Shen, I-Chao; Chen, Bing-Yu; Stam, Jos and Mitra, Niloy J. and Xu, Kun
A person's handwriting appears differently within a typical range of variations, and the shapes of handwriting characters also show complex interaction with their nearby neighbors. This makes automatic synthesis of handwriting characters and paragraphs very challenging. In this paper, we propose a method for synthesizing handwriting texts according to a writer's handwriting style. The synthesis algorithm is composed by two phases. First, we create the multidimensional morphable models for different characters based on one writer's data. Then, we compute the cursive probability to decide whether each pair of neighboring characters are conjoined together or not. By jointly modeling the handwriting style and conjoined property through a novel trajectory optimization, final handwriting words can be synthesized from a set of collected samples. Furthermore, the paragraphs' layouts are also automatically generated and adjusted according to the writer's style obtained from the same dataset. We demonstrate that our method can successfully synthesize an entire paragraph that mimic a writer's handwriting using his/her collected handwriting samples.
Deformable Objects Collision Handling with Fast Convergence
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Li, Siwang; Pan, Zherong; Huang, Jin; Bao, Hujun; Jin, Xiaogang; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We present a stable and efficient simulator for deformable objects with collisions and contacts. For stability, an optimization derived from the implicit time integrator is solved in each timestep under the inequality constraints coming from collisions. To achieve fast convergence, we extend the MPRGP based solver from handling box constraints only to handling general linear constraints and prove its convergence. This generalization introduces a cost of solving dense linear systems in each step, but these systems can be reduced into diagonal ones for efficiency without affecting the general stability via pruning redundant collisions. Our solver is an order of magnitude faster, especially for elastic objects under large deformation compared with iterative constraint anticipation method (ICA), a typical method for stability. The efficiency, robustness and stability are further verified by our results.
DenseCut: Densely Connected CRFs for Realtime GrabCut
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Cheng, Ming-Ming; Prisacariu, Victor Adrian; Zheng, Shuai; Torr, Philip H. S.; Rother, Carsten; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Figure-ground segmentation from bounding box input, provided either automatically or manually, has been extremely popular in the last decade and influenced various applications. A lot of research has focused on highquality segmentation, using complex formulations which often lead to slow techniques, and often hamper practical usage. In this paper we demonstrate a very fast segmentation technique which still achieves very high quality results. We propose to replace the time consuming iterative refinement of global colour models in traditional GrabCut formulation by a densely connected CRF. To motivate this decision, we show that a dense CRF implicitly models unnormalized global colour models for foreground and background. Such relationship provides insightful analysis to bridge between dense CRF and GrabCut functional. We extensively evaluate our algorithm using two famous benchmarks. Our experimental results demonstrated that the proposed algorithm achieves an order of magnitude (10 ) speed-up with respect to the closest competitor, and at the same time achieves a considerably higher accuracy.
Dispersion-based Color Projection using Masked Prisms
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Hostettler, Rafael; Habel, Ralf; Gross, Markus; Jarosz, Wojciech; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We present a method for projecting arbitrary color images using a white light source and an optical device with no colored components - consisting solely of one or two prisms and two transparent masks. When illuminated, the first mask creates structured white light that is then dispersed in the prism and attenuated by the second mask to create the color projection. We derive analytical expressions for the mask parameters from the physical components and validate our approach both in simulation and also demonstrate it on a wide variety of images using two different physical setups (one consisting of two inexpensive triangular prisms, and the other using a single rhombic prism). Furthermore, we show that optimizing the masks simultaneously enables obfuscating the image content, and provides a tradeoff between increased light throughput (by up to a factor of three) and maximum color saturation.
EasyXplorer: A Flexible Visual Exploration Approach for Multivariate Spatial Data
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Wu, Feiran; Chen, Guoning; Huang, Jin; Tao, Yubo; Chen, Wei; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Exploring multivariate spatial data attracts much attention in the visualization community. The main challenge lies in that automatic analysis techniques is insufficient in discovering complicated patterns with the perspective of human beings, while visualization techniques are incapable of accurately identifying the features of interest. This paper addresses this contradiction by enhancing automatic analysis techniques with human intelligence in an iterative visual exploration process. The integrated system, called EasyXplorer, provides a suite of intuitive clustering, dimension reduction, visual encoding and filtering widgets within 2D and 3D views, allowing an inexperienced user to visually explore and reason undiscovered features with several simple interactions. Case studies show the quality and scalability of our approach in quite challenging examples.
An Efficient Boundary Handling with a Modified Density Calculation for SPH
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Fujisawa, Makoto; Miura, Kenjiro T.; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We propose a new boundary handling method for smoothed particle hydrodynamics (SPH). Previous approaches required the use of boundary particles to prevent particles from sticking to the boundary. We address this issue by correcting the fundamental equations of SPH with the integration of a kernel function. Our approach is able to directly handle triangle mesh boundaries without the need for boundary particles.We also show how our approach can be integrated into a position-based fluid framework.
An Efficient Feathering System with Collision Control
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Liu, Le; Li, Xiaosheng; Chen, Yanyun; Liu, Xuehui; Zhang, Jian J.; Wu, Enhua; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We present an efficient interactive system for dressing a naked bird with feathers. In our system, a skeleton associated with guide feathers is used to describe the distribution of the body feathers. The special skeleton can be easily built by the user, given a 3D bird model as input. To address the problem of interpenetrations among feathers, the growth priority between the feather roots is defined, with which we obtain the growth order from a greedily constructed directed acyclic graph. Each feather is then adjusted in that order by a height field based collision resolution process. The height field not only provides an efficient way to detect the collision but also enables us to finely control the degree of collision during feather adjustments. The results show that our approach is capable of resolving the collisions among thousands of feathers in a few seconds. If model animation is desired, the feathers can be adjusted on the fly at interactive framerates. Details of our implementation are provided with several examples to demonstrate the effectiveness of our system.
Efficient Variational Light Field View Synthesis For Making Stereoscopic 3D Images
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhang, Lei; Zhang, Yu-Hang; Huang, Hua; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We present a novel approach for making stereoscopic images by variational view synthesis on the multi-perspective light field. With the intended disparities as constraints, we specialize the generative variational model by incorporating per-pixel viewpoint assignment to synthesize the stereo pair. Also, we improve the variational solution by use of explicit weighted average on the light field. Our algorithm is able to handle arbitrary disparity remapping, thus enabling more flexible disparity control for the desired stereoscopic effect. The experiments demonstrate the effectiveness and efficiency for making the stereoscopic 3D images based on the light field.
Evaluating the Quality of Face Alignment without Ground Truth
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Sheng, Kekai; Dong, Weiming; Kong, Yan; Mei, Xing; Li, Jilin; Wang, Chengjie; Huang, Feiyue; Hu, Bao-Gang; Stam, Jos and Mitra, Niloy J. and Xu, Kun
The study of face alignment has been an area of intense research in computer vision, with its achievements widely used in computer graphics applications. The performance of various face alignment methods is often imagedependent or somewhat random because of their own strategy. This study aims to develop a method that can select an input image with good face alignment results from many results produced by a single method or multiple ones. The task is challenging because different face alignment results need to be evaluated without any ground truth. This study addresses this problem by designing a feasible feature extraction scheme to measure the quality of face alignment results. The feature is then used in various machine learning algorithms to rank different face alignment results. Our experiments show that our method is promising for ranking face alignment results and is able to pick good face alignment results, which can enhance the overall performance of a face alignment method with a random strategy. We demonstrate the usefulness of our ranking-enhanced face alignment algorithm in two practical applications: face cartoon stylization and digital face makeup.
FlexyFont: Learning Transferring Rules for Flexible Typeface Synthesis
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Phan, Huy Quoc; Fu, Hongbo; Chan, Antoni B.; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Maintaining consistent styles across glyphs is an arduous task in typeface design. In this work we introduce Flexy- Font, a flexible tool for synthesizing a complete typeface that has a consistent style with a given small set of glyphs. Motivated by a key fact that typeface designers often maintain a library of glyph parts to achieve a consistent typeface, we intend to learn part consistency between glyphs of different characters across typefaces. We take a part assembling approach by firstly decomposing the given glyphs into semantic parts and then assembling them according to learned sets of transferring rules to reconstruct the missing glyphs. To maintain style consistency, we represent the style of a font as a vector of pairwise part similarities. By learning a distribution over these feature vectors, we are able to predict the style of a novel typeface given only a few examples. We utilize a popular machine learning method as well as retrieval-based methods to quantitatively assess the performance of our feature vector, resulting in favorable results. We also present an intuitive interface that allows users to interactively create novel typefaces with ease. The synthesized fonts can be directly used in real-world design.
Frontmatter: Pacific Graphics 2015
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Stam, Jos; Mitra, Niloy J.; Xu, Kun; -
Geometrically Exact Simulation of Inextensible Ribbon
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Shen, Zhongwei; Huang, Jin; Chen, Wei; Bao, Hujun; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Narrow, inextensible, and naturally flat ribbons have some special and interesting phenomena under isometric deformations. Although a ribbon has a shape between rod and shell, directly applying the geometric representation designed for them imposes a challenge to faithfully reproduce interesting behaviors. We thus parameterize the ribbon surface as a developable ruled surface along its centerline and represent it using a framed centerline curve. Then the elastic and kinetic energy of the ribbon surface can be equivalently yet compactly described by the framed centerline curve only. To avoid numerical singularity when developability is violated, a finite Taylor series approximation to the potential energy is adopted. Under the observation that the off-centerline part of ribbon contributes little dynamic effect, the kinetic energy is simplified with respect to the centerline velocity only. For efficiency, each time step is separated into two stages: dynamically evolving the centerline, and then quasi-statically updating the ruling. We validate the method with qualitative analysis and ribbon specific phenomena comparisons with real-world scenarios. A set of comparisons to rod and shell model is also provided to demonstrate the advantages of our method.
Guided Mesh Normal Filtering
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhang, Wangyu; Deng, Bailin; Zhang, Juyong; Bouaziz, Sofien; Liu, Ligang; Stam, Jos and Mitra, Niloy J. and Xu, Kun
The joint bilateral filter is a variant of the standard bilateral filter, where the range kernel is evaluated using a guidance signal instead of the original signal. It has been successfully applied to various image processing problems, where it provides more flexibility than the standard bilateral filter to achieve high quality results. On the other hand, its success is heavily dependent on the guidance signal, which should ideally provide a robust estimation about the features of the output signal. Such a guidance signal is not always easy to construct. In this paper, we propose a novel mesh normal filtering framework based on the joint bilateral filter, with applications in mesh denoising. Our framework is designed as a two-stage process: first, we apply joint bilateral filtering to the face normals, using a properly constructed normal field as the guidance; afterwards, the vertex positions are updated according to the filtered face normals. We compute the guidance normal on a face using a neighboring patch with the most consistent normal orientations, which provides a reliable estimation of the true normal even with a high-level of noise. The effectiveness of our approach is validated by extensive experimental results.
Interactive Rigging with Intuitive Tools
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Bang, Seungbae; Choi, Byungkuk; Ribera, Roger Blanco i; Kim, Meekyoung; Lee, Sung-Hee; Noh, Junyong; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Rigging is a core element in the process of bringing a 3D character to life. The rig defines and delimits the motions of the character and provides an interface for an animator with which to interact with the 3D character. The quality of the rig has a key impact on the expressiveness of the character. Creating a usable, rich, production ready rig is a laborious task requiring direct intervention by a trained professional because the goal is difficult to achieve with fully automatic methods. We propose a semi-automatic rigging editing framework which eases the need for manual intervention while maintaining an important degree of control over the final rig. Starting by automatically generated base rig, we provide interactive operations which efficiently configure the skeleton structure and mesh skinning.
Mesh Denoising using Extended ROF Model with L1 Fidelity
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Wu, Xiaoqun; Zheng, Jianmin; Cai, Yiyu; Fu, Chi-Wing; Stam, Jos and Mitra, Niloy J. and Xu, Kun
This paper presents a variational algorithm for feature-preserved mesh denoising. At the heart of the algorithm is a novel variational model composed of three components: fidelity, regularization and fairness, which are specifically designed to have their intuitive roles. In particular, the fidelity is formulated as an L1 data term, which makes the regularization process be less dependent on the exact value of outliers and noise. The regularization is formulated as the total absolute edge-lengthed supplementary angle of the dihedral angle, making the model capable of reconstructing meshes with sharp features. In addition, an augmented Lagrange method is provided to efficiently solve the proposed variational model. Compared to the prior art, the new algorithm has crucial advantages in handling large scale noise, noise along random directions, and different kinds of noise, including random impulsive noise, even in the presence of sharp features. Both visual and quantitative evaluation demonstrates the superiority of the new algorithm.
Multi-layer Lattice Model for Real-Time Dynamic Character Deformation
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Iwamoto, Naoya; Shum, Hubert P. H.; Yang, Longzhi; Morishima, Shigeo; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Due to the recent advancement of computer graphics hardware and software algorithms, deformable characters have become more and more popular in real-time applications such as computer games. While there are mature techniques to generate primary deformation from skeletal movement, simulating realistic and stable secondary deformation such as jiggling of fats remains challenging. On one hand, traditional volumetric approaches such as the finite element method require higher computational cost and are infeasible for limited hardware such as game consoles. On the other hand, while shape matching based simulations can produce plausible deformation in real-time, they suffer from a stiffness problem in which particles either show unrealistic deformation due to high gains, or cannot catch up with the body movement. In this paper, we propose a unified multi-layer lattice model to simulate the primary and secondary deformation of skeleton-driven characters. The core idea is to voxelize the input character mesh into multiple anatomical layers including the bone, muscle, fat and skin. Primary deformation is applied on the bone voxels with lattice-based skinning. The movement of these voxels is propagated to other voxel layers using lattice shape matching simulation, creating a natural secondary deformation. Our multi-layer lattice framework can produce simulation quality comparable to those from other volumetric approaches with a significantly smaller computational cost. It is best to be applied in real-time applications such as console games or interactive animation creation.
Multiple Facial Image Editing Using Edge-Aware PDE Learning
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Liang, Lingyu; Jin, Lianwen; Zhang, Xin; Xu, Yong; Stam, Jos and Mitra, Niloy J. and Xu, Kun
This paper introduces a novel facial editing tool, called edge-aware mask, to achieve multiple photo-realistic rendering effects in a unified framework. The edge-aware masks facilitate three basic operations for adaptive facial editing, including region selection, edit setting and region blending. Inspired by the state-of-the-art edit propagation and partial differential equation (PDE) learning method, we propose an adaptive PDE model with facial priors for masks generation through edge-aware diffusion. The edge-aware masks can automatically fit the complex region boundary with great accuracy and produce smooth transition between different regions, which significantly improves the visual consistence of face editing and reduce the human intervention. Then, a unified and flexible facial editing framework is constructed, which consists of layer decomposition, edge-aware masks generation, and layer/mask composition. The combinations of multiple facial layers and edge-aware masks can achieve various facial effects simultaneously, including face enhancement, relighting, makeup and face blending etc. Qualitative and quantitative evaluations were performed using different datasets for different facial editing tasks. Experiments demonstrate the effectiveness and flexibility of our methods, and the comparisons with the previous methods indicate that improved results are obtained using the combination of multiple edge-aware masks.

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