29-Issue 7

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https://diglib.eg.org/handle/10.2312/158

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Video Painting via Motion Layer Manipulation
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Huang, Hua; Zhang, Lei; Fu, Tian-Nan
Temporal coherence is an important problem in Non-Photorealistic Rendering for videos. In this paper, we present a novel approach to enhance temporal coherence in video painting. Instead of painting on video frame, our approach first partitions the video into multiple motion layers, and then places the brush strokes on the layers to generate the painted imagery. The extracted motion layers consist of one background layer and several object layers in each frame. Then, background layers from all the frames are aligned into a panoramic image, on which brush strokes are placed to paint the background in one-shot. The strokes used to paint object layers are propagated frame by frame using smooth transformations defined by thin plate splines. Once the background and object layers are painted, they are projected back to each frame and blent to form the final painting results. Thanks to painting a single image, our approach can completely eliminate the flickering in background, and temporal coherence on object layers is also significantly enhanced due to the smooth transformation over frames. Additionally, by controlling the painting strokes on different layers, our approach is easy to generate painted video with multi-style. Experimental results show that our approach is both robust and efficient to generate plausible video painting.
Modeling Complex Unfoliaged Trees from a Sparse Set of Images
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lopez, Luis D.; Ding, Yuanyuan; Yu, Jingyi
We present a novel image-based technique for modeling complex unfoliaged trees. Existing tree modeling tools either require capturing a large number of views for dense 3D reconstruction or rely on user inputs and botanic rules to synthesize natural-looking tree geometry. In this paper, we focus on faithfully recovering real instead of realistically-looking tree geometry from a sparse set of images. Our solution directly integrates 2D/3D tree topology as shape priors into the modeling process. For each input view, we first estimate a 2D skeleton graph from its matte image and then find a 2D skeleton tree from the graph by imposing tree topology. We develop a simple but effective technique for computing the optimal 3D skeleton tree most consistent with the 2D skeletons. For each edge in the 3D skeleton tree, we further apply volumetric reconstruction to recover its corresponding curved branch. Finally, we use piecewise cylinders to approximate each branch from the volumetric results. We demonstrate our framework on a variety of trees to illustrate the robustness and usefulness of our technique.
Binary Orientation Trees for Volume and Surface Reconstruction from Unoriented Point Clouds
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Chen, Yi-Ling; Chen, Bing-Yu; Lai, Shang-Hong; Nishita, Tomoyuki
Given a complete unoriented point set, we propose a binary orientation tree (BOT) for volume and surface representation, which roughly splits the space into the interior and exterior regions with respect to the input point set. The BOTs are constructed by performing a traditional octree subdivision technique while the corners of each cell are associated with a tag indicating the in/out relationship with respect to the input point set. Starting from the root cell, a growing stage is performed to efficiently assign tags to the connected empty sub-cells. The unresolved tags of the remaining cell corners are determined by examining their visibility via the hidden point removal operator. We show that the outliers accompanying the input point set can be effectively detected during the construction of the BOTs. After removing the outliers and resolving the in/out tags, the BOTs are ready to support any volume or surface representation techniques. To represent the surfaces, we also present a modified MPU implicits algorithm enabled to reconstruct surfaces from the input unoriented point clouds by taking advantage of the BOTs.
Feature Oriented Progressive Lossless Mesh Coding
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Peng, Jingliang; Huang, Yan; Kuo, C.-C. Jay; Eckstein, Ilya; Gopi, M.
A feature-oriented generic progressive lossless mesh coder (FOLProM) is proposed to encode triangular meshes with arbitrarily complex geometry and topology. In this work, a sequence of levels of detail (LODs) are generated through iterative vertex set split and bounding volume subdivision. The incremental geometry and connectivity updates associated with each vertex set split and/or bounding volume subdivision are entropy coded. Due to the visual importance of sharp geometric features, the whole geometry coding process is optimized for a better presentation of geometric features, especially at low coding bitrates. Feature-oriented optimization in FOLProM is performed in hierarchy control and adaptive quantization. Efficient coordinate representation and prediction schemes are employed to reduce the entropy of data significantly. Furthermore, a simple yet efficient connectivity coding scheme is proposed. It is shown that FOLProM offers a significant rate-distortion (R-D) gain over the prior art, which is especially obvious at low bitrates.
Dirichlet Harmonic Shape Compression with Feature Preservation for Parameterized Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Liu, Yang; Prabhakaran, Balakrishnan; Guo, Xiaohu
With the rapid advancement of 3D scanning devices, large and complicated 3D shapes are becoming ubiquitous, and require large amount of resources to store and transmit them efficiently. This makes shape compression a demanding technique in order for the user to reduce the data transmission latency. Existing shape compression methods could achieve very low bit-rates by sacrificing shape quality. But none of them guarantees the preservation of salient feature lines that users care. In addition, many 3D shapes come with parametric information for texture mapping purposes. In this paper we describe a spectral method to compress the geometric shapes equipped with arbitrary valid parametric information. It guarantees to preserve user-specified feature lines while achieving a high compression ratio. By applying the spectral shape analysis - Dirichlet Manifold Harmonics, in the 2D parametric domain, this method provides a progressive compression mechanism to trade-off between bit-rate and shape quality. Experiments show that this method provides very low bit-rate with high shape-quality and still guarantees the preservation of user-specified feature lines.
Fast Updating of Delaunay Triangulation of Moving Points by Bi-cell Filtering
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Zhou, Yuanfeng; Sun, Feng; Wang, Wenping; Wang, Jiaye; Zhang, Caiming
Updating a Delaunay triangulation when data points are slightly moved is the bottleneck of computation time in variational methods for mesh generation and remeshing. Utilizing the connectivity coherence between two consecutive Delaunay triangulations for computation speedup is the key to solving this problem. Our contribution is an effective filtering technique that confirms most bi-cells whose Delaunay connectivities remain unchanged after the points are perturbed. Based on bi-cell flipping, we present an efficient algorithm for updating two-dimensional and three-dimensional Delaunay triangulations of dynamic point sets. Experimental results show that our algorithm outperforms previous methods.
Modeling of Clouds from a Single Photograph
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Dobashi, Yoshinori; Shinzo, Yusuke; Yamamoto, Tsuyoshi
In this paper, we propose a simple method for modeling clouds from a single photograph. Our method can synthesize three types of clouds: cirrus, altocumulus, and cumulus. We use three different representations for each type of cloud: two-dimensional texture for cirrus, implicit functions (metaballs) for altocumulus, and volume data for cumulus. Our method initially computes the intensity and the opacity of clouds for each pixel from an input photograph, stored as a cloud image. For cirrus, the cloud image is the output two-dimensional texture. For each of the other two types of cloud, three-dimensional density distributions are generated by referring to the cloud image. Since the method is very simple, the computational cost is low. Our method can generate, within several seconds, realistic clouds that are similar to those in the photograph.
Multi-Resolution Cloth Simulation
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lee, Yongjoon; Yoon, Sung-eui; Oh, Seungwoo; Kim, Duksu; Choi, Sunghee
We propose a novel, multi-resolution method to efficiently perform large-scale cloth simulation. Our cloth simulation method is based on a triangle-based energy model constructed from a cloth mesh. We identify that solutions of the linear system of cloth simulation are smooth in certain regions of the cloth mesh and solve the linear system on those regions in a reduced solution space. Then we reconstruct the original solutions by performing a simple interpolation from solutions computed in the reduced space. In order to identify regions where solutions are smooth, we propose simplification metrics that consider stretching, shear, and bending forces, as well as geometric collisions. Our multi-resolution method can be applied to many existing cloth simulation methods, since our method works on a general linear system. In order to demonstrate benefits of our method, we apply our method into four large-scale cloth benchmarks that consist of tens or hundreds of thousands of triangles. Because of the reduced computations, we achieve a performance improvement by a factor of up to one order of magnitude, with a little loss of simulation quality.
Towards Perceptual Simplification of Models with Arbitrary Materials
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Menzel, Nicolas; Guthe, Michael
Real-time rendering of models with high polygon count is still an important issue in interactive computer graphics. A common way to improve rendering performance is to generate different levels of detail of a model. These are mostly computed using polygonal simplification techniques, which aim to reduce the number of polygons without significant loss of visual fidelity. Most existing algorithms use geometric error bounds, which are well-suited for silhouette preservation. They ignore the fact that a much more aggressive simplification is possible in low-contrast areas inside the model. The main contribution of this paper is an efficient simplification algorithm based on the human visual system. The key idea is to move the domain of error computation from image-space to vertex-space to avoid a costly per-pixel comparison. This way the error estimation of a simplification operation can be accelerated significantly. To account for the human vision, we introduce a perceptually based metric depending on the contrast and spatial frequency of the model at a single vertex. Finally, we validate our approach with a user study.
Automatic Animation for Time-Varying Data Visualization
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Yu, Li; Lu, Aidong; Ribarsky, William; Chen, Wei
This paper presents a digital storytelling approach that generates automatic animations for time-varying data visualization. Our approach simulates the composition and transition of storytelling techniques and synthesizes animations to describe various event features. Specifically, we analyze information related to a given event and abstract it as an event graph, which represents data features as nodes and event relationships as links. This graph embeds a tree-like hierarchical structure which encodes data features at different scales. Next, narrative structures are built by exploring starting nodes and suitable search strategies in this graph. Different stages of narrative structures are considered in our automatic rendering parameter decision process to generate animations as digital stories. We integrate this animation generation approach into an interactive exploration process of time-varying data, so that more comprehensive information can be provided in a timely fashion. We demonstrate with a storm surge application that our approach allows semantic visualization of time-varying data and easy animation generation for users without special knowledge about the underlying visualization techniques.
Fast Particle-based Visual Simulation of Ice Melting
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Iwasaki, K.; Uchida, H.; Dobashi, Y.; Nishita, T.
The visual simulation of natural phenomena has been widely studied. Although several methods have been proposed to simulate melting, the flows of meltwater drops on the surfaces of objects are not taken into account. In this paper, we propose a particle-based method for the simulation of the melting and freezing of ice objects and the interactions between ice and fluids. To simulate the flow of meltwater on ice and the formation of water droplets, a simple interfacial tension is proposed, which can be easily incorporated into common particle-based simulation methods such as Smoothed Particle Hydrodynamics. The computations of heat transfer, the phase transition between ice and water, the interactions between ice and fluids, and the separation of ice due to melting are further accelerated by implementing our method using CUDA. We demonstrate our simulation and rendering method for depicting melting ice at interactive frame-rates.
Image Synthesis for Branching Structures
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Sibbing, Dominik; Pavic, Darko; Kobbelt, Leif
We present a set of techniques for the synthesis of artificial images that depict branching structures like rivers, cracks, lightning, mountain ranges, or blood vessels. The central idea is to build a statistical model that captures the characteristic bending and branching structure from example images. Then a new skeleton structure is synthesized and the final output image is composed from image fragments of the original input images. The synthesis part of our algorithm runs mostly automatic but it optionally allows the user to control the process in order to achieve a specific result. The combination of the statistical bending and branching model with sophisticated fragment-based image synthesis corresponds to a multi-resolution decomposition of the underlying branching structure into the low frequency behavior (captured by the statistical model) and the high frequency detail (captured by the image detail in the fragments). This approach allows for the synthesis of realistic branching structures, while at the same time preserving important textural details from the original image.
Condenser-Based Instant Reflectometry
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lan, Yanxiang; Dong, Yue; Wang, Jiaping; Tong, Xin; Guo, Baining
We present a technique for rapid capture of high quality bidirectional reflection distribution functions(BRDFs) of surface points. Our method represents the BRDF at each point by a generalized microfacet model with tabulated normal distribution function (NDF) and assumes that the BRDF is symmetrical. A compact and light-weight reflectometry apparatus is developed for capturing reflectance data from each surface point within one second. The device consists of a pair of condenser lenses, a video camera, and six LED light sources. During capture, the reflected rays from a surface point lit by a LED lighting are refracted by a condenser lenses and efficiently collected by the camera CCD. Taking advantage of BRDF symmetry, our reflectometry apparatus provides an efficient optical design to improve the measurement quality. We also propose a model fitting algorithm for reconstructing the generalized microfacet model from the sparse BRDF slices captured from a material surface point. Our new algorithm addresses the measurement errors and generates more accurate results than previous work. Our technique provides a practical and efficient solution for BRDF acquisition, especially for materials with anisotropic reflectance. We test the accuracy of our approach by comparing our results with ground truth. We demonstrate the efficiency of our reflectometry by measuring materials with different degrees of specularity, values of Fresnel factor, and angular variation.
Semi-isometric Registration of Line Features for Flexible Fitting of Protein Structures
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Abeysinghe, S.S.; Baker, M. L.; Chiu, W.; Ju, T.
In this paper, we study a registration problem that is motivated by a practical biology problem - fitting protein structures to low-re solution density maps. We consider registration between two sets of lines features (e.g., helices in the proteins) that have undergone not a single, but multiple isometric transformations (e.g., hinge-motions). The problem is further complicated by the presence of symmetry in each set. We formulate the problem as a clique-finding problem in a product graph, and propose a heuristic solution that includes a fast clique-finding algorithm unique to the structure of this graph. When tested on a suite of real protein structures, the algorithm achieved high accuracy even for very large inputs containing hundreds of helices.
L4RW: Laziness-based Realistic Real-time Responsive Rebalance in Walking
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Xu, Mingliang; Li, Huansen; Lv, Pei; Chen, Wenzhi; Liu, Gengdai; Zhu, Pengyu; Pan, Zhigeng
We present a novel L4RW (Laziness-based Realistic Real-time Responsive Rebalance in Walking) technique to synthesize 4RW animations under unexpected external perturbations with minimal locomotion effort. We first devise a lazy dynamic rebalance model, which specifies the dynamic balance conditions, defines the rebalance effort, and selects the suitable rebalance strategy automatically using the laziness law after an unexpected perturbation. Based on the model, L4RW searches over a motion capture (mocap) database for an appropriate motion segment to follow, and the transition-to motions is generated by interpolating the active response dynamic motion. A support vector machine (SVM) based training, classification, and predication algorithm is applied to reduce the search space, and it is trained offline only once. Our algorithm classifies the mocap database into many rebalance strategy-specified subsets and then online predicts responsive motions in the subset according to the selected strategy. The rebalance effort, the extrapolated center of mass (XCoM) and environment constraints are selected as feature attributes for the SVM feature vector. Furthermore, the subset s segments are sorted through the rebalance effort, then our algorithm searches for an acceptable segment starting from the least-effort segment. Compared with previous methods, our search increases speed by over two orders of magnitude, and our algorithm creates more realistic and smooth 4RW animation.
Manifold-Based 3D Face Caricature Generation with Individualized Facial Feature Extraction
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Wang, S.F.; Lai, S.H.
Caricature is an interesting art to express exaggerated views of different persons and things through drawing. The face caricature is popular and widely used for different applications. To do this, we have to properly extract unique/specialized features of a person s face. A person s facial feature not only depends on his/her natural appearance, but also the associated expression style. Therefore, we would like to extract the neutural facial features and personal expression style for different applicaions. In this paper, we represent the 3D neutral face models in BU-3DFE database by sparse signal decomposition in the training phase. With this decomposition, the sparse training data can be used for robust linear subspace modeling of public faces. For an input 3D face model, we fit the model and decompose the 3D model geometry into a neutral face and the expression deformation separately. The neutral geomertry can be further decomposed into public face and individualized facial feature. We exaggerate the facial features and the expressions by estimating the probability on the corresponding manifold. The public face, the exaggerated facial features and the exaggerated expression are combined to synthesize a 3D caricature for a 3D face model. The proposed algorithm is automatic and can effectively extract the individualized facial features from an input 3D face model to create 3D face caricature.
Creating and Preserving Vortical Details in SPH Fluid
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Zhu, Bo; Yang, Xubo; Fan, Ye
We present a new method to create and preserve the turbulent details generated around moving objects in SPH fluid. In our approach, a high-resolution overlapping grid is bounded to each object and translates with the object. The turbulence formation is modeled by resolving the local flow around objects using a hybrid SPH-FLIP method. Then these vortical details are carried on SPH particles flowing through the local region and preserved in the global field in a synthetic way. Our method provides a physically plausible way to model the turbulent details around both rigid and deformable objects in SPH fluid, and can efficiently produce animations of complex gaseous phenomena with rich visual details.
Metalights: Improved Interleaved Shading
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Faure, William; Chang, Chun-Fa
We present metalights, a novel Virtual Point Light (VPL) encapsulating structure which enhances classic interleaved shading by improving VPL sampling, based on few initial screen space samples to estimate VPL contribution to current view. Our method leads to important noise variance reduction in the final picture by only adding a small fraction of computation. The implementation is straight-forward and well adapted to both CPU and GPU-based engines. We also present different image-space assignment schemes for the VPL subsets to break the regularity of the noise pattern or to adapt it to simple antialiasing.
Frontmatter PG 2010
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
Instant Propagation of Sparse Edits on Images and Videos
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Li, Yong; Ju, Tao; Hu, Shi-Min
The ability to quickly and intuitively edit digital contents has become increasingly important in our everyday life. We propose a novel method for propagating a sparse set of user edits (e.g., changes in color, brightness, contrast, etc.) expressed as casual strokes to nearby regions in an image or video with similar appearances. Existing methods for edit propagation are typically based on optimization, whose computational cost can be prohibitive for large inputs. We re-formulate propagation as a function interpolation problem in a high-dimensional space, which we solve very efficiently using radial basis functions. While simple to implement, our method significantly improves the speed and space cost of existing methods, and provides instant feedback of propagation results even on large images and videos.

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