34-Issue 7

Permanent URI for this collection

Tsinghua University, Beijing, October 7 – 9, 2015

Shape and Mesh
Projective Feature Learning for 3D Shapes with Multi-View Depth Images
Zhige Xie, Kai Xu, Wen Shan, Ligang Liu, Yueshan Xiong, and Hui Huang
Object Completion using k-Sparse Optimization
Pavlos Mavridis, Ivan Sipiran, Anthousis Andreadis, and Georgios Papaioannou
Guided Mesh Normal Filtering
Wangyu Zhang, Bailin Deng, Juyong Zhang, Sofien Bouaziz, and Ligang Liu
Mesh Denoising using Extended ROF Model with L1 Fidelity
Xiaoqun Wu, Jianmin Zheng, Yiyu Cai, and Chi-Wing Fu
Procedural Tree Modeling with Guiding Vectors
Ling Xu and David Mould
Rendering
Realtime Rendering Glossy to Glossy Reflections in Screen Space
Chao Xu, Rui Wang, and Hujun Bao
Order-Independent Transparency for Programmable Deferred Shading Pipelines
Andre Schollmeyer, Andrey Babanin, and Bernd Froehlich
Towards Automatic Band-Limited Procedural Shaders
Jonathan Dorn, Connelly Barnes, Jason Lawrence, and Westley Weimer
Virtual Spherical Gaussian Lights for Real-time Glossy Indirect Illumination
Yusuke Tokuyoshi
Characters
Multi-layer Lattice Model for Real-Time Dynamic Character Deformation
Naoya Iwamoto, Hubert P. H. Shu, Longzhi Yang, and Shigeo Morishima
A Suggestive Interface for Sketch-based Character Posing
Pei Lv, Pengjie Wang, Weiwei Xu, Jinxiang Chai, Mingmin Zhang, Zhigeng Pan, and Mingliang Xu
Interactive Rigging with Intuitive Tools
Seungbae Bang, Byungkuk Choi, Roger Blanco i Ribera, Meekyoung Kim, Sung-Hee Lee, and Junyong Noh
Simulation and Visualization
Quadratic Contact Energy Model for Multi-impact Simulation
Tianxiang Zhang, Sheng Li, Dinesh Manocha, Guoping Wang, and Hanqiu Sun
Geometrically Exact Simulation of Inextensible Ribbon
Zhongwei Shen, Jin Huang, Wei Chen, and Hujun Bao
An Efficient Boundary Handling with a Modified Density Calculation for SPH
Makoto Fujisawa and Kenjiro T. Miura
EasyXplorer: A Flexible Visual Exploration Approach for Multivariate Spatial Data
Feiran Wu, Guoning Chen, Jin Huang, Yubo Tao, and Wei Chen
Image and Video
4D Model Flow: Precomputed Appearance Alignment for Real-time 4D Video Interpolation
Dan Casas, Christian Richardt, John Collomosse, Christian Theobalt, and Adrian Hilton
Efficient Variational Light Field View Synthesis For Making Stereoscopic 3D Images
Lei Zhang, Yu-Hang Zhang, and Hua Huang
DenseCut: Densely Connected CRFs for Realtime GrabCut
Ming-Ming Cheng, Victor Adrian Prisacariu, Shuai Zheng, Philip H. S. Torr, and Carsten Rother
Multiple Facial Image Editing Using Edge-Aware PDE Learning
Lingyu Liang, Lianwen Jin, Xin Zhang, and Yong Xu
Evaluating the Quality of Face Alignment without Ground Truth
Kekai Sheng, Weiming Dong, Yan Kong, Xing Mei, Jilin Li, Chengjie Wang, Feiyue Huang, and Bao-Gang Hu
Drawing and Painting
Tone- and Feature-Aware Circular Scribble Art
Chun-Chia Chiu, Yi-Hsiang Lo, Ruen-Rone Lee, and Hung-Kuo Chu
Data-driven Handwriting Synthesis in a Conjoined Manner
Hsin-I Chen, Tse-Ju Lin, Xiao-Feng Jian, I-Chao Shen, Bing-Yu Chen
FlexyFont: Learning Transferring Rules for Flexible Typeface Synthesis
Huy Quoc Phan, Hongbo Fu, and Antoni B. Chan
Brushables: Example-based Edge-aware Directional Texture Painting
Michal Lukáč, Jakub Fišer, Paul Asente, Jingwan Lu, Eli Shechtman, and Daniel Sýkora
Collision Detection
Deformable Objects Collision Handling with Fast Convergence
Siwang Li, Zherong Pan, Jin Huang, Hujun Bao, and Xiaogang Jin
An Efficient Feathering System with Collision Control
Le Liu, Xiaosheng Li, Yanyun Chen, Xuehui Liu, Jian J. Zhang, and Enhua Wu
TightCCD: Efficient and Robust Continuous Collision Detection using Tight Error Bounds
Zhendong Wang, Min Tang, Ruofeng Tong, and Dinesh Manocha
Ray Tracing
Skeleton based Vertex Connection Resampling for Bidirectional Path Tracing
Laurent Noël and Venceslas Biri
Ray Specialized Contraction on Bounding Volume Hierarchies
Yan Gu, Yong He, and Guy E. Blelloch
Stylization
Contrast-Enhanced Black and White Images
Hua Li and David Mould
Dispersion-based Color Projection using Masked Prisms
Rafael Hostettler, Ralf Habel, Markus Gross, and Wojciech Jarosz
PIXEL2BRICK: Constructing Brick Sculptures from Pixel Art
Ming-Hsun Kuo, You-En Lin, Hung-Kuo Chu, Ruen-Rone Lee, and Yong-Liang Yang

BibTeX (34-Issue 7)
                
@article{
10.1111:cgf.12740,
journal = {Computer Graphics Forum}, title = {{
Projective Feature Learning for 3D Shapes with Multi-View Depth Images}},
author = {
Xie, Zhige
and
Xu, Kai
and
Shan, Wen
and
Liu, Ligang
and
Xiong, Yueshan
and
Huang, Hui
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12740}
}
@inproceedings{
10.1111:cgf.12773,
booktitle = {
Preface and Table of Contents},
editor = {
-
}, title = {{
Frontmatter: Pacific Graphics 2015}},
author = {
Stam, Jos
and
Mitra, Niloy J.
and
Xu, Kun
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12773}
}
                
@article{
10.1111:cgf.12741,
journal = {Computer Graphics Forum}, title = {{
Object Completion using k-Sparse Optimization}},
author = {
Mavridis, Pavlos
and
Sipiran, Ivan
and
Andreadis, Anthousis
and
Papaioannou, Georgios
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12741}
}
                
@article{
10.1111:cgf.12742,
journal = {Computer Graphics Forum}, title = {{
Guided Mesh Normal Filtering}},
author = {
Zhang, Wangyu
and
Deng, Bailin
and
Zhang, Juyong
and
Bouaziz, Sofien
and
Liu, Ligang
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12742}
}
                
@article{
10.1111:cgf.12744,
journal = {Computer Graphics Forum}, title = {{
Procedural Tree Modeling with Guiding Vectors}},
author = {
Xu, Ling
and
Mould, David
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12744}
}
                
@article{
10.1111:cgf.12743,
journal = {Computer Graphics Forum}, title = {{
Mesh Denoising using Extended ROF Model with L1 Fidelity}},
author = {
Wu, Xiaoqun
and
Zheng, Jianmin
and
Cai, Yiyu
and
Fu, Chi-Wing
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12743}
}
                
@article{
10.1111:cgf.12745,
journal = {Computer Graphics Forum}, title = {{
Realtime Rendering Glossy to Glossy Reflections in Screen Space}},
author = {
Xu, Chao
and
Wang, Rui
and
Bao, Hujun
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12745}
}
                
@article{
10.1111:cgf.12746,
journal = {Computer Graphics Forum}, title = {{
Order-Independent Transparency for Programmable Deferred Shading Pipelines}},
author = {
Schollmeyer, Andre
and
Babanin, Andrey
and
Froehlich, Bernd
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12746}
}
                
@article{
10.1111:cgf.12747,
journal = {Computer Graphics Forum}, title = {{
Towards Automatic Band-Limited Procedural Shaders}},
author = {
Dorn, Jonathan
and
Barnes, Connelly
and
Lawrence, Jason
and
Weimer, Westley
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12747}
}
                
@article{
10.1111:cgf.12748,
journal = {Computer Graphics Forum}, title = {{
Virtual Spherical Gaussian Lights for Real-time Glossy Indirect Illumination}},
author = {
Tokuyoshi, Yusuke
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12748}
}
                
@article{
10.1111:cgf.12749,
journal = {Computer Graphics Forum}, title = {{
Multi-layer Lattice Model for Real-Time Dynamic Character Deformation}},
author = {
Iwamoto, Naoya
and
Shum, Hubert P. H.
and
Yang, Longzhi
and
Morishima, Shigeo
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12749}
}
                
@article{
10.1111:cgf.12750,
journal = {Computer Graphics Forum}, title = {{
A Suggestive Interface for Sketch-based Character Posing}},
author = {
Lv, Pei
and
Wang, Pengjie
and
Xu, Weiwei
and
Chai, Jinxiang
and
Zhang, Mingmin
and
Pan, Zhigeng
and
Xu, Mingliang
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12750}
}
                
@article{
10.1111:cgf.12752,
journal = {Computer Graphics Forum}, title = {{
Quadratic Contact Energy Model for Multi-impact Simulation}},
author = {
Zhang, Tianxiang
and
Li, Sheng
and
Manocha, Dinesh
and
Wang, Guoping
and
Sun, Hanqiu
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12752}
}
                
@article{
10.1111:cgf.12751,
journal = {Computer Graphics Forum}, title = {{
Interactive Rigging with Intuitive Tools}},
author = {
Bang, Seungbae
and
Choi, Byungkuk
and
Ribera, Roger Blanco i
and
Kim, Meekyoung
and
Lee, Sung-Hee
and
Noh, Junyong
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12751}
}
                
@article{
10.1111:cgf.12753,
journal = {Computer Graphics Forum}, title = {{
Geometrically Exact Simulation of Inextensible Ribbon}},
author = {
Shen, Zhongwei
and
Huang, Jin
and
Chen, Wei
and
Bao, Hujun
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12753}
}
                
@article{
10.1111:cgf.12755,
journal = {Computer Graphics Forum}, title = {{
EasyXplorer: A Flexible Visual Exploration Approach for Multivariate Spatial Data}},
author = {
Wu, Feiran
and
Chen, Guoning
and
Huang, Jin
and
Tao, Yubo
and
Chen, Wei
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12755}
}
                
@article{
10.1111:cgf.12754,
journal = {Computer Graphics Forum}, title = {{
An Efficient Boundary Handling with a Modified Density Calculation for SPH}},
author = {
Fujisawa, Makoto
and
Miura, Kenjiro T.
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12754}
}
                
@article{
10.1111:cgf.12756,
journal = {Computer Graphics Forum}, title = {{
4D Model Flow: Precomputed Appearance Alignment for Real-time 4D Video Interpolation}},
author = {
Casas, Dan
and
Richardt, Christian
and
Collomosse, John
and
Theobalt, Christian
and
Hilton, Adrian
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12756}
}
                
@article{
10.1111:cgf.12758,
journal = {Computer Graphics Forum}, title = {{
DenseCut: Densely Connected CRFs for Realtime GrabCut}},
author = {
Cheng, Ming-Ming
and
Prisacariu, Victor Adrian
and
Zheng, Shuai
and
Torr, Philip H. S.
and
Rother, Carsten
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12758}
}
                
@article{
10.1111:cgf.12757,
journal = {Computer Graphics Forum}, title = {{
Efficient Variational Light Field View Synthesis For Making Stereoscopic 3D Images}},
author = {
Zhang, Lei
and
Zhang, Yu-Hang
and
Huang, Hua
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12757}
}
                
@article{
10.1111:cgf.12760,
journal = {Computer Graphics Forum}, title = {{
Evaluating the Quality of Face Alignment without Ground Truth}},
author = {
Sheng, Kekai
and
Dong, Weiming
and
Kong, Yan
and
Mei, Xing
and
Li, Jilin
and
Wang, Chengjie
and
Huang, Feiyue
and
Hu, Bao-Gang
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12760}
}
                
@article{
10.1111:cgf.12759,
journal = {Computer Graphics Forum}, title = {{
Multiple Facial Image Editing Using Edge-Aware PDE Learning}},
author = {
Liang, Lingyu
and
Jin, Lianwen
and
Zhang, Xin
and
Xu, Yong
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12759}
}
                
@article{
10.1111:cgf.12761,
journal = {Computer Graphics Forum}, title = {{
Tone- and Feature-Aware Circular Scribble Art}},
author = {
Chiu, Chun-Chia
and
Lo, Yi-Hsiang
and
Lee, Ruen-Rone
and
Chu, Hung-Kuo
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12761}
}
                
@article{
10.1111:cgf.12763,
journal = {Computer Graphics Forum}, title = {{
FlexyFont: Learning Transferring Rules for Flexible Typeface Synthesis}},
author = {
Phan, Huy Quoc
and
Fu, Hongbo
and
Chan, Antoni B.
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12763}
}
                
@article{
10.1111:cgf.12762,
journal = {Computer Graphics Forum}, title = {{
Data-driven Handwriting Synthesis in a Conjoined Manner}},
author = {
Chen, Hsin-I
and
Lin, Tse-Ju
and
Jian, Xiao-Feng
and
Shen, I-Chao
and
Chen, Bing-Yu
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12762}
}
                
@article{
10.1111:cgf.12764,
journal = {Computer Graphics Forum}, title = {{
Brushables: Example-based Edge-aware Directional Texture Painting}},
author = {
Lukáč, Michal
and
Fišer, Jakub
and
Asente, Paul
and
Lu, Jingwan
and
Shechtman, Eli
and
Sýkora, Daniel
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12764}
}
                
@article{
10.1111:cgf.12767,
journal = {Computer Graphics Forum}, title = {{
TightCCD: Efficient and Robust Continuous Collision Detection using Tight Error Bounds}},
author = {
Wang, Zhendong
and
Tang, Min
and
Tong, Ruofeng
and
Manocha, Dinesh
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12767}
}
                
@article{
10.1111:cgf.12766,
journal = {Computer Graphics Forum}, title = {{
An Efficient Feathering System with Collision Control}},
author = {
Liu, Le
and
Li, Xiaosheng
and
Chen, Yanyun
and
Liu, Xuehui
and
Zhang, Jian J.
and
Wu, Enhua
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12766}
}
                
@article{
10.1111:cgf.12765,
journal = {Computer Graphics Forum}, title = {{
Deformable Objects Collision Handling with Fast Convergence}},
author = {
Li, Siwang
and
Pan, Zherong
and
Huang, Jin
and
Bao, Hujun
and
Jin, Xiaogang
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12765}
}
                
@article{
10.1111:cgf.12768,
journal = {Computer Graphics Forum}, title = {{
Skeleton based Vertex Connection Resampling for Bidirectional Path Tracing}},
author = {
Noël, Laurent
and
Biri, Venceslas
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12768}
}
                
@article{
10.1111:cgf.12769,
journal = {Computer Graphics Forum}, title = {{
Ray Specialized Contraction on Bounding Volume Hierarchies}},
author = {
Gu, Yan
and
He, Yong
and
Blelloch, Guy E.
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12769}
}
                
@article{
10.1111:cgf.12770,
journal = {Computer Graphics Forum}, title = {{
Contrast-Enhanced Black and White Images}},
author = {
Li, Hua
and
Mould, David
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12770}
}
                
@article{
10.1111:cgf.12771,
journal = {Computer Graphics Forum}, title = {{
Dispersion-based Color Projection using Masked Prisms}},
author = {
Hostettler, Rafael
and
Habel, Ralf
and
Gross, Markus
and
Jarosz, Wojciech
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12771}
}
                
@article{
10.1111:cgf.12772,
journal = {Computer Graphics Forum}, title = {{
PIXEL2BRICK: Constructing Brick Sculptures from Pixel Art}},
author = {
Kuo, Ming-Hsun
and
Lin, You-En
and
Chu, Hung-Kuo
and
Lee, Ruen-Rone
and
Yang, Yong-Liang
}, year = {
2015},
publisher = {
The Eurographics Association and John Wiley & Sons Ltd.},
DOI = {
10.1111/cgf.12772}
}

Browse

Recent Submissions

Now showing 1 - 34 of 34
  • Item
    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.
  • Item
    Frontmatter: Pacific Graphics 2015
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Stam, Jos; Mitra, Niloy J.; Xu, Kun; -
  • Item
    Object Completion using k-Sparse Optimization
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Mavridis, Pavlos; Sipiran, Ivan; Andreadis, Anthousis; Papaioannou, Georgios; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    We present a new method for the completion of partial globally-symmetric 3D objects, based on the detection of partial and approximate symmetries in the incomplete input dataset. In our approach, symmetry detection is formulated as a constrained sparsity maximization problem, which is solved efficiently using a robust RANSACbased optimizer. The detected partial symmetries are then reused iteratively, in order to complete the missing parts of the object. A global error relaxation method minimizes the accumulated alignment errors and a nonrigid registration approach applies local deformations in order to properly handle approximate symmetry. Unlike previous approaches, our method does not rely on the computation of features, it uniformly handles translational, rotational and reflectional symmetries and can provide plausible object completion results, even on challenging cases, where more than half of the target object is missing. We demonstrate our algorithm in the completion of 3D scans with varying levels of partiality and we show the applicability of our approach in the repair and completion of heavily eroded or incomplete cultural heritage objects.
  • Item
    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.
  • Item
    Procedural Tree Modeling with Guiding Vectors
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Xu, Ling; Mould, David; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    We propose guiding vectors to augment graph-based tree synthesis, in which trees are collections of least-cost paths in a graph. Each node has an associated guiding vector; edges parallel to the guiding vector are cheap, but edges are more expensive when their orientation differs from the guiding vector.We further propose an incremental method for assigning guiding vectors over the graph, in which a node's guiding vector is an incremental rotation of that of its parent. We present a complete procedural system for tree modeling; our use of guiding vectors enables the graph-based method to produce high-quality tree models resembling a variety of real-world tree species.
  • Item
    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.
  • Item
    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.
  • Item
    Order-Independent Transparency for Programmable Deferred Shading Pipelines
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Schollmeyer, Andre; Babanin, Andrey; Froehlich, Bernd; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    In this paper, we present a flexible and efficient approach for the integration of order-independent transparency into a deferred shading pipeline. The intermediate buffers for storing fragments to be shaded are extended with a dynamic and memory-efficient storage for transparent fragments. The transparency of an object is not fixed and remains programmable until fragment processing, which allows for the implementation of advanced materials effects, interaction techniques or adaptive fade-outs. Traversing costs for shading the transparent fragments are greatly reduced by introducing a tile-based light-culling pass. During deferred shading, opaque and transparent fragments are shaded and composited in front-to-back order using the retrieved lighting information and a physically-based shading model. In addition, we discuss various configurations of the system and further enhancements. Our results show that the system performs at interactive frame rates even for complex scenarios.
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    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.
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    Virtual Spherical Gaussian Lights for Real-time Glossy Indirect Illumination
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Tokuyoshi, Yusuke; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    Virtual point lights (VPLs) are well established for real-time global illumination. However, this method suffers from spiky artifacts and flickering caused by singularities of VPLs, highly glossy materials, high-frequency textures, and discontinuous geometries. To avoid these artifacts, this paper introduces a virtual spherical Gaussian light (VSGL) which roughly represents a set of VPLs. For a VSGL, the total radiant intensity and positional distribution of VPLs are approximated using spherical Gaussians and a Gaussian distribution, respectively. Since this approximation can be computed using summations of VPL parameters, VSGLs can be dynamically generated using mipmapped reflective shadow maps. Our VSGL generation is simple and independent from any scene geometries. In addition, reflected radiance for a VSGL is calculated using an analytic formula. Hence, we are able to render one-bounce glossy interreflections at real-time frame rates with smaller artifacts.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.
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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.
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    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.
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    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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    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.
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    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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    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.
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    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.
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    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.
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    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.
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    TightCCD: Efficient and Robust Continuous Collision Detection using Tight Error Bounds
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Wang, Zhendong; Tang, Min; Tong, Ruofeng; Manocha, Dinesh; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    We present a realtime and reliable continuous collision detection (CCD) algorithm between triangulated models that exploits the floating point hardware capability of current CPUs and GPUs. Our formulation is based on Bernstein Sign Classification that takes advantage of the geometry properties of Bernstein basis and Bézier curves to perform Boolean collision queries. We derive tight numerical error bounds on the computations and employ those bounds to design an accurate algorithm using finite-precision arithmetic. Compared with prior floatingpoint CCD algorithms, our approach eliminates all the false negatives and 90-95% of the false positives. We integrated our algorithm (TightCCD) with physically-based simulation system and observe speedups in collision queries of 5-15X compared with prior reliable CCD algorithms. Furthermore, we demonstrate its benefits in terms of improving the performance or robustness of cloth simulation systems.
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    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.
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    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.
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    Skeleton based Vertex Connection Resampling for Bidirectional Path Tracing
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Noël, Laurent; Biri, Venceslas; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    Bidirectional path tracing is known to perform poorly for the rendering of highly occluded scenes. Indeed, the connection strategy between light and eye subpaths does not take into account the visibility factor, presenting no contribution for many sampled paths. To improve the efficiency of bidirectional path tracing, we propose a new method for adaptive resampling of connections between light and eye subpaths. Aiming for this objective, we build discrete probability distributions of light subpaths based on a skeleton of the empty space of the scene. In order to demonstrate the efficiency of our algorithm, we compare our method to both standard bidirectional path tracing and a recent important caching method.
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    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.
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    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.
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    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.
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    PIXEL2BRICK: Constructing Brick Sculptures from Pixel Art
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Kuo, Ming-Hsun; Lin, You-En; Chu, Hung-Kuo; Lee, Ruen-Rone; Yang, Yong-Liang; Stam, Jos and Mitra, Niloy J. and Xu, Kun
    LEGO, a popular brick-based toy construction system, provides an affordable and convenient way of fabricating geometric shapes. However, building arbitrary shapes using LEGO bricks with restrictive colors and sizes is not trivial. It requires careful design process to produce appealing, stable and constructable brick sculptures. In this work, we investigate the novel problem of constructing brick sculptures from pixel art images. In contrast to previous efforts that focus on 3D models, pixel art contains rich visual contents for generating engaging LEGO designs. On the other hand, the characteristics of pixel art and corresponding brick sculpture pose new challenges to the design process. We present PIXEL2BRICK, a novel computational framework to automatically construct brick sculptures from pixel art. This is based on implementing a set of design guidelines concerning the visual quality as well as the structural stability of built sculptures. We demonstrate the effectiveness of our framework with various brick sculptures (both real and virtual) generated from a variety of pixel art images. Experimental results show that our framework is efficient and gains significant improvements over state-of-the-arts.