29-Issue 7

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

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B-Mesh: A Modeling System for Base Meshes of 3D Articulated Shapes
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Ji, Zhongping; Liu, Ligang; Wang, Yigang
This paper presents a novel modeling system, called B-Mesh, for generating base meshes of 3D articulated shapes. The user only needs to draw a one-dimensional skeleton and to specify key balls at the skeletal nodes. The system then automatically generates a quad dominant initial mesh. Further subdivision and evolution are performed to refine the initial mesh and generate a quad mesh which has good edge flow along the skeleton directions. The user can also modify and manipulate the shape by editing the skeleton and the key balls and can easily compose new shapes by cutting and pasting existing models in our system. The mesh models generated in our system greatly benefit the sculpting operators for sculpting modeling and skeleton-based animation.
Variance Soft Shadow Mapping
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Yang, Baoguang; Dong, Zhao; Feng, Jieqing; Seidel, Hans-Peter; Kautz, Jan
We present variance soft shadow mapping (VSSM) for rendering plausible soft shadow in real-time. VSSM is based on the theoretical framework of percentage-closer soft shadows (PCSS) and exploits recent advances in variance shadow mapping (VSM). Our new formulation allows for the efficient computation of (average) blocker distances, a common bottleneck in PCSS-based methods. Furthermore, we avoid incorrectly lit pixels commonly encountered in VSM-based methods by appropriately subdividing the filter kernel. We demonstrate that VSSM renders high-quality soft shadows efficiently (usually over 100 fps) for complex scene settings. Its speed is at least one order of magnitude faster than PCSS for large penumbra.
Density-based Outlier Rejection in Monte Carlo Rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2010) DeCoro, Christopher; Weyrich, Tim; Rusinkiewicz, Szymon
The problem of noise in Monte-Carlo rendering arising from estimator variance is well-known and well-studied. In this work, we concentrate on identifying individual light paths as outliers that lead to significant spikes of noise and represent a challenge for existing filtering methods. Most noise-reduction methods, such as importance sampling and stratification, attempt to generate samples that are expected a priori to have lower variance, but do not take into account actual sample values. While these methods are essential to decrease overall noise, we show that filtering samples a posteriori allows for greater reduction of spiked noise. In particular, given evaluated sample values, outliers can be identified and removed. Conforming with conventions in statistics, we emphasize that the term outlier should not be taken as synonymous with incorrect , but as referring to samples that distort the empirically-observed distribution of energy relative to the true underlying distribution. By expressing a path distribution in joint image and color space, we show how outliers can be characterized by their density across the set of all nearby paths in this space. We show that removing these outliers leads to significant improvements in rendering quality.
Context-Dependent Crowd Evaluation
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lerner, Alon; Chrysanthou, Yiorgos; Shamir, Ariel; Cohen-Or, Daniel
Many times, even if a crowd simulation looks good in general, there could be some specific individual behaviors which do not seem correct. Spotting such problems manually can become tedious, but ignoring them may harm the simulation s credibility. In this paper we present a data-driven approach for evaluating the behaviors of individuals within a simulated crowd. Based on video-footage of a real crowd, a database of behavior examples is generated. Given a simulation of a crowd, an analog analysis is performed on it, defining a set of queries, which are matched by a similarity function to the database examples. The results offer a possible objective answer to the question of how similar are the simulated individual behaviors to real observed behaviors. Moreover, by changing the video input one can change the context of evaluation. We show several examples of evaluating simulated crowds produced using different techniques and comprising of dense crowds, sparse crowds and flocks.
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)
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.
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.
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.
Real-time Depth of Field Rendering via Dynamic Light Field Generation and Filtering
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Yu, Xuan; Wang, Rui; Yu, Jingyi
We present a new algorithm for efficient rendering of high-quality depth-of-field (DoF) effects. We start with a single rasterized view (reference view) of the scene, and sample the light field by warping the reference view to nearby views. We implement the algorithm using NVIDIA s CUDA to achieve parallel processing, and exploit the atomic operations to resolve visibility when multiple pixels warp to the same image location. We then directly synthesize DoF effects from the sampled light field. To reduce aliasing artifacts, we propose an image-space filtering technique that compensates for spatial undersampling using MIP mapping. The main advantages of our algorithm are its simplicity and generality. We demonstrate interactive rendering of DoF effects in several complex scenes. Compared to existing methods, ours does not require ray tracing and hence scales well with scene complexity.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.

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