34-Issue 7

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

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Frontmatter: Pacific Graphics 2015
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Stam, Jos; Mitra, Niloy J.; Xu, Kun; -
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.
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.
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.
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.
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.
Realtime Rendering Glossy to Glossy Reflections in Screen Space
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Xu, Chao; Wang, Rui; Bao, Hujun; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Glossy to glossy reflections are lights bounced between glossy surfaces. Such directional light transports are important for humans to perceive glossy materials, but difficult to simulate. This paper proposes a new method for rendering screen-space glossy to glossy reflections in realtime. We use spherical von Mises-Fisher (vMF) distributions to model glossy BRDFs at surfaces, and employ screen space directional occlusion (SSDO) rendering framework to trace indirect light transports bounced in the screen space. As our main contributions, we derive a new parameterization of vMF distribution so as to convert the non-linear fit of multiple vMF distributions into a linear sum in the new space. Then, we present a new linear filtering technique to build MIP-maps on glossy BRDFs, which allows us to create filtered radiance transfer functions at runtime, and efficiently estimate indirect glossy to glossy reflections. We demonstrate our method in a realtime application for rendering scenes with dynamic glossy objects. Compared with screen space directional occlusion, our approach only requires one extra texture and has a negligible overhead, 3% ˜ 6% loss at frame rate, but enables glossy to glossy reflections.
Ray Specialized Contraction on Bounding Volume Hierarchies
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Gu, Yan; He, Yong; Blelloch, Guy E.; Stam, Jos and Mitra, Niloy J. and Xu, Kun
In this paper we propose a simple but effective method to modify a BVH based on ray distribution for improved ray tracing performance. Our method starts with an initial BVH generated by any state-of-the-art offline algorithm. Then by traversing a small set of sample rays we collect statistics at each node of the BVH. Finally, a simple but ultra-fast BVH contraction algorithm modifies the initial binary BVH to a multi-way BVH. The overall acceleration for ray-primitive testing is about 25% for incoherent diffuse rays and 30% for shadow rays, which is significant as a data structure optimization. Similar results are also presented for packet ray tracing, and for Quad-BVHs the improvement is 10% to 15%. The approach has the advantages of being simple, and compatible with almost any existing BVH and ray tracing techniques, and it require very little extra work to generate the modified tree.
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.
Tone- and Feature-Aware Circular Scribble Art
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Chiu, Chun-Chia; Lo, Yi-Hsiang; Lee, Ruen-Rone; Chu, Hung-Kuo; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Circular scribble art is a kind of line drawing where the seemingly random, noisy and shapeless circular scribbles at microscopic scale constitute astonishing grayscale images at macroscopic scale. Such a delicate skill has rendered the creation of circular scribble art a tedious and time-consuming task even for gifted artists. In this work, we present a novel method for automatic synthesis of circular scribble art. The synthesis problem is modeled as tracing along a virtual path using a parametric circular curve. To reproduce the tone and important edge structure of input grayscale images, the system adaptively adjusts the density and structure of virtual path, and dynamically controls the size, drawing speed and orientation of parametric circular curve during the synthesis.We demonstrate the potential of our system using several circular scribble images synthesized from a wide variety of grayscale images. A preliminary experimental studying is conducted to qualitatively and quantitatively evaluate our method. Results report that our method is efficient and generates convincing results comparable to artistic artworks.
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.
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.
Quadratic Contact Energy Model for Multi-impact Simulation
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhang, Tianxiang; Li, Sheng; Manocha, Dinesh; Wang, Guoping; Sun, Hanqiu; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Simultaneous multi-impact simulation is a challenging problem that frequently arises in physically-based modeling of rigid bodies. There are several physical criteria that should be satisfied for rigid body collision handling, but existing methods generally fail to meet one or more of them. In order to capture the inner process of potential energy variation, which is the physical foundation of collisions in a multi-impact system, we present a novel quadratic contact energy model for rigid body simulation. By constructing quadratic energy functions with respect to the impulses, post-impact reactions of rigid bodies can be computed efficiently. Our model can satisfy the physical criteria and can simulate various natural phenomena including the wave effect. Also, our model can be easily combined with Linear Complementary Problem (LCP) and can provide feasible results with any restitution coefficient. In practice, our model can solve the simultaneous multi-impact problem efficiently and robustly, and we highlight its performance on different benchmarks.
Projective Feature Learning for 3D Shapes with Multi-View Depth Images
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Xie, Zhige; Xu, Kai; Shan, Wen; Liu, Ligang; Xiong, Yueshan; Huang, Hui; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Feature learning for 3D shapes is challenging due to the lack of natural paramterization for 3D surface models. We adopt the multi-view depth image representation and propose Multi-View Deep Extreme Learning Machine (MVD-ELM) to achieve fast and quality projective feature learning for 3D shapes. In contrast to existing multiview learning approaches, our method ensures the feature maps learned for different views are mutually dependent via shared weights and in each layer, their unprojections together form a valid 3D reconstruction of the input 3D shape through using normalized convolution kernels. These lead to a more accurate 3D feature learning as shown by the encouraging results in several applications. Moreover, the 3D reconstruction property enables clear visualization of the learned features, which further demonstrates the meaningfulness of our feature learning.
Towards Automatic Band-Limited Procedural Shaders
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Dorn, Jonathan; Barnes, Connelly; Lawrence, Jason; Weimer, Westley; Stam, Jos and Mitra, Niloy J. and Xu, Kun
Procedural shaders are a vital part of modern rendering systems. Despite their prevalence, however, procedural shaders remain sensitive to aliasing any time they are sampled at a rate below the Nyquist limit. Antialiasing is typically achieved through numerical techniques like supersampling or precomputing integrals stored in mipmaps. This paper explores the problem of analytically computing a band-limited version of a procedural shader as a continuous function of the sampling rate. There is currently no known way of analytically computing these integrals in general. We explore the conditions under which exact solutions are possible and develop several approximation strategies for when they are not. Compared to supersampling methods, our approach produces shaders that are less expensive to evaluate and closer to ground truth in many cases. Compared to mipmapping or precomputation, our approach produces shaders that support an arbitrary bandwidth parameter and require less storage. We evaluate our method on a range of spatially-varying shader functions, automatically producing antialiased versions that have comparable error to 4x4 multisampling but can be over an order of magnitude faster. While not complete, our approach is a promising first step toward this challenging goal and indicates a number of interesting directions for future work.
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.
A Suggestive Interface for Sketch-based Character Posing
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Lv, Pei; Wang, Pengjie; Xu, Weiwei; Chai, Jinxiang; Zhang, Mingmin; Pan, Zhigeng; Xu, Mingliang; Stam, Jos and Mitra, Niloy J. and Xu, Kun
We present a user-friendly suggestive interface for sketch-based character posing. Our interface provides suggestive information on the sketching canvas in succession by combining image retrieval technique with 3D character posing, while the user is drawing. The system highlights the canvas region where the user should draw on and constrains the user's sketches in a reasonable solution space. This is based on an e cient image descriptor, which is used to measure the distance between the user's sketch and 2D views of 3D poses. In order to achieve faster query response, local sensitive hashing is involved in our system. In addition, sampling-based optimization algorithm is adopted to synthesize and optimize the retrieved 3D pose to match the user's sketches the best. Experiments show that our interface can provide smooth suggestive information to improve the reality of sketching poses and shorten the time required for 3D posing.
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.
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.
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.

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