PG: Pacific Graphics Short Papers

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A Fast Simulation Method Using SPH and Wavelet for Sub-Particle-Scale Turbulent Flow
(The Eurographics Association, 2011) Fujisawa, Makoto; Mimura, Go; Amano, Toshiyuki; Miyazaki, Jun; Kato, Hirokazu; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
This paper presents a fast simulation method for turbulent flow which uses a particle method and wavelet analysis. To simulate fluid flow, the method uses smoothed particle hydrodynamics (SPH), which discretizes the fluid into a collection of particles, and detects regions where turbulent flow will occur by using wavelet analysis without a spatial grid. By taking the curl of wavelet noise, the turbulent flow is then appended as a divergence-free turbulence velocity field. Additionally, by using vortex subparticles, which characterize the vortex features of turbulence, a subparticle-scale representation of turbulent flow is proposed. Implementing almost all processes on a graphics processing unit (GPU), simulations are performed in near real time.
Diffusion Tensor Weighted Harmonic Fields for Feature Classification
(The Eurographics Association, 2011) Wang, Shengfa; Hou, Tingbo; Su, Zhixun; Qin, Hong; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
This paper presents an efficient method for feature definition and classification on shapes. We tackle this challenge by exploring the weighted harmonic field (WHF), which is also the stable state of a heat diffusion regulated by an anisotropic diffusion tensor. The technical merit of our method is highlighted by the elegant integration of locallydefined diffusion tensor and globally-defined harmonic field in an anisotropic manner. At the computational front, the partial differential equation of heat diffusion becomes a linear system with Dirichlet boundary condition at heat sources (also called seeds). We develop an algorithm for automatic seed selection, enhanced by a fast update procedure in a high dimensional space. Various experiments are conducted to demonstrate the ease of manipulation and high performance of our method.
Illustrative Line Styles for Flow Visualization
(The Eurographics Association, 2011) Everts, Maarten H.; Bekker, Henk; Roerdink, Jos B. T. M.; Isenberg, Tobias; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
We present a flexible illustrative line style model for the visualization of streamline data. Our model partitions vieworiented line strips into parallel bands whose basic visual properties can be controlled independently. We thus extend previous line stylization techniques specifically for visualization purposes by allowing the parametrization of these bands based on the local line data attributes. We demonstrate the effectiveness of our model by applying it to 3D flow field datasets.
Fast Level Set Image Segmentation Using New Evolution Indicator Operators
(The Eurographics Association, 2011) Xiao, Chunxia; Gan, Jiajia; Hu, Xiangyun; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
We propose an effective level set evolution method for robust object segmentation in real images. We construct an effective region indicator and a multiscale edge indicator to adaptively guide the evolution of the level set function. The region indicator is built on the similarity map between image pixels and user specified interest regions, which is computed using Gaussian Mixture Models (GMM). To accurately detect object boundary, we propose to use a multi-scale edge indicator defined in the gradient domain of the multi-scale feature-preserving filtered image. Then, we develop a new mixing edge stop function based on these two indicators, which forces the level set to evolve adaptively based on the image content. Furthermore, we apply an acceleration approach to speed up our evolution process, which yields real time segmentation performance. As the results show, our approach is effective for image segmentation and works well to accurately detect the complex object boundaries in real-time.
Facial Retargeting by Adding Supplemental Blendshapes
(The Eurographics Association, 2011) Kim, Paul Hyunjin; Seol, Yeongho; Song, Jaewon; Noh, Junyong; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
This paper introduces a novel method to add a minimal set of missing blendshapes to automatically improve the quality of the retargeting result. Our approach compares the expression spaces defined by the source and the target to determine which frames need to be corrected. The expression spaces are represented on the principal axes extracted from the target blendshapes. Those frames that cannot be sufficiently reconstructed by the current set of blendshapes will be augmented by a set of automatically generated blendshapes. The new blendshapes are determined to minimize error between the source animation and the retargeting result. We performed experiments to compare the results created by a basic set of blendshapes and by our method. Our method effectively reduces error between the source and target animation, and produces much visually improved target animation without relying on manual intervention.
Feature-Aware Reconstruction of Volume Data via Trivariate Splines
(The Eurographics Association, 2011) Li, Bo; Qin, Hong; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
In this paper, we propose a novel approach that transforms discrete volumetric data directly acquired from scanning devices into continuous spline representation with tensor-product regular structure. Our method is achieved through three major steps as follows. First, in order to capture fine features, we construct an as-smooth-as-possible frame field, satisfying a sparse set of directional constraints. Next, a globally smooth parameterization is computed, with iso-parameter curves following the frame field directions. We utilize the parameterization to remesh the data and construct a set of regular-structured volumetric patch layouts, consisting of a small number of volumetric patches while enforcing good feature alignment. Finally, we construct trivariate T-splines on all patches to model geometry and density functions simultaneously. Compared with conventional discrete data, our data-splineconversion results are more efficient and compact, serving as a powerful toolkit with broader application appeal in shape modeling, GPU computing, data reduction, scientific visualization, and physical analysis.
Feature Adaptive Surfel Set Simplification
(The Eurographics Association, 2011) Huang, Yan; Yan, Feihu; Wang, Bei; Peng, Jingliang; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
In this paper we propose a novel scheme for simplifying a surfel set with the resultant surfels computed and distributed in an effort to preserve prominent geometric and textural features with a reduced number of primitives. It works by iteratively collapsing local neighborhoods around surfels until a desired data reduction ratio is reached. The local neighborhood collapses are prioritized according to a cost metric that takes into account the local complexities of both the geometric and the textural information. Experimental results demonstrate that, besides yielding outstanding model quality at a reduced model size, the proposed scheme provides the flexibility for the users to specify the relative priorities in the geometric and the textural fidelity.
Interactive Design of Planar Curved Folding by Reflection
(The Eurographics Association, 2011) Mitani, Jun; Igarashi, Takeo; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
Designing curved folds of a developable surface remains an open problem. No analytical method for the design of curved folds has been reported. Although optimization methods exist, it is difficult to interactively design valid curved folds of a single developable surface using such methods. In the present paper, we propose an interactive system for designing a surface with planar curved folds based on mirror reflection. The key consideration is that a surface created by sequential reflective folding is guaranteed to be isometrically unfolded into a plane. We demonstrate that the proposed system enables the interactive design of a variety of expressive curved folds, which was very difficult using previous methods.
An Image-based Hair Styling System Using Layered Texture Pieces
(The Eurographics Association, 2011) Watanabe, Hiroki; Kanamori, Yoshihiro; Mitani, Jun; Fukui, Yukio; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
We present an interactive system that allows the user to finely edit a hairstyle image so that the image can be naturally synthesized onto a given facial image. In our system, a hairstyle is composed by stacking texture pieces (textured belt-shaped polygons) that represent hair wisps. By warping these pieces, the user can perform typical manipulations for hairstyles, such as lengthening/shortening, combing (modification of the flows of hair) and scissoring. We demonstrate the effectiveness of our system through experimental results with various hairstyle images and facial images.
An Effective and Efficient Contour-based Corner Detector using Simple Triangular Theory
(The Eurographics Association, 2011) Sadat, R. M. Najmus; Teng, Shyh Wei; Lu, Guojun; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
Corner detection is an important operation in many computer vision applications. Among the contour-based corner detectors in the literature, the Chord-to-Point Distance Accumulation (CPDA) detector is reported to have one of the best repeatability and lowest localization error. However, we found that CPDA detector often fails to accurately detect the true corners in some situations. Furthermore, CPDA detector is also computationally expensive. To overcome these weaknesses of CPDA detector, we propose an effective but yet efficient corner detector using a simple triangular theory. Our experimental results show that our proposed detector outperforms CPDA and six other existing detectors in terms of repeatability. Our proposed detector also has one of the lowest localization error. Finally it is computationally the most efficient.
Fast Computing Adaptively Sampled Distance Field on GPU
(The Eurographics Association, 2011) Yin, Kangxue; Liu, Youquan; Wu, Enhua; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
In this paper we present an efficient method to compute the signed distance field for a large triangle mesh, which can run interactively with GPU accelerated. Restricted by absence of flexible pointer addressing on GPU, we design a novel multi-layer hash table to organize the voxel/triangle overlap pairs as two-tuples, such strategy provides an efficient way to store and access. Based on the general octree structure idea, a GPU-based octree structure is given to generate the sample points which are used to calculate the shortest distance to the triangle mesh. Classifying sample points into three types provides a well tradeoff between performance and precision, and when implementing the algorithm on GPU, these samples are also organized into blocks to share the triangles among threads to save bandwidth. Finally we demonstrate efficient calculation of the global signed distance field for some typical large triangle meshes with pseudo-normal method. Compared to previous work, our algorithm is quite fast in performance.
Sketch-based Breaking Waves
(The Eurographics Association, 2011) Zhang, Guijuan; Wen, Gaojin; Zhu, Dengming; Lu, Dianjie; Feng, Shengzhong; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
We present a sketching method for animating breaking waves in this paper. Our approach allows an animator to control physically-based wave breaking effects by drawing the outline of the wave shape intuitively. To do this, we provide a feature-based keyframe design model. We can sketch the wave shape roughly and describe the wave shape as a unified volume representation. Moreover, we propose an efficient keyframe matching model to transport current fluid state to the target state with minimum energy. The solution to the keyframe matching model is used to compute the external force field for the Navier-Stokes equations. Our method is straightforward to implement and convenient to produce interesting wave breaking behaviors. The experimental results show that our method is easy and intuitive to use.
Visualizing Local Weather Characteristics Interpreted from Glider GPS Flight Logs
(The Eurographics Association, 2011) Hsieh, Tung-Ju; Kuester, Falko; Hutchinson, Tara; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
Visualization can aid in improving the validation and evaluation of glider flight logs, which in turn can make the logs more meaningful in flight evaluation and planning. This paper presents techniques to interpret and visualize local weather characteristics derived from glider flight logs. Although glider flight logs only contain discretely sampled position and elevation records, local weather characteristics such as thermal lift and wind velocity can be interpreted from the temporal and spatial components in the logs. A total number of 397 flight logs were used in this study, statistics were performed to identify strong thermal locations, maximum flight altitudes, and weather patterns along flight routes. When the derived thermal features are geo-referenced with 3D terrain models, results support post-flight evaluation and pre-flight planning. For a given flight task, the pilot can derive an optimal flight path based on the presented visualization techniques and the statistics obtained from the historical records.
Virtual City Map Generation using Area Subdivision
(The Eurographics Association, 2011) Müller, Kerstin; Heischbourg, Luc; Fünfzig, Christoph; Petsch, Sebastian; Hagen, Hans; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
In this paper we present a new approach to build typical street networks for urban and rural areas automatically. Most street networks have a characteristic appearance which is a mixture between a kind of a regular spreading of streets and various perturbations of the regular structure, e.g., caused by the terrain. Our City Map Generation (CMG) algorithm gets as input an height field including watercourses and restricted areas such as nature protection areas or mountain areas. Furthermore, the user can specify the urbanization by the number of city centers or by a density map. The CMG algorithm produces a street map for the given landscape based on rules, which the user can also modify to obtain an individual appearance. Additionally, the regular structure is varied by a set of rules incorporating randomness. The results can be used to generate models for city areas, e.g., in movies and commercials. Depending on the demands, our flexible approach can be adjusted to produce a variety of road maps automatically. We show some examples and demonstrate that our algorithm is easy to implement and to use.
Feature-Aware Mesh for Image Retargeting
(The Eurographics Association, 2011) Niu, Yuzhen; Liu, Feng; Lai, Yu-chi; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
Image retargeting adapts an input image to displays other than originally intended while minimizing visual distortion. Most warping-based methods formulate retargeting as a spatially-varying warping problem over a uniform mesh and encourage each mesh grid to undergo a conformal transformation to minimize visual distortion. However, the conformal transformation constraint on each individual mesh grid is often insufficient to preserve global image structures. In this paper, we present a feature-aware mesh based retargeting method. Our idea is to warp each visually salient image feature as a whole, thus preserving global image structures. Our method divides an image into a non-uniform mesh such that each salient image feature or object is enclosed only in one mesh element. Our method warps each mesh element with an affine transformation. We then formulate image retargeting as a spatially-varying affine warping problem. To further minimize the distortion, we encourage each affine transformation to be close to more distortion-free ones, such as conformal transformation. The spatially-varying affine warping problem is formulated as a quadratic energy minimization problem, which can be solved efficiently. Our experiments demonstrate that our method can effectively preserve global image structures.
Perceptually-based Stroke Pattern Synthesis
(The Eurographics Association, 2011) Liu, Dongwei; Zhang, Junsong; Zhou, Changle; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
We present a novel method to synthesize stroke patterns from a user-specified vector reference pattern. The main idea is inspired by research in visual perception. We first extract the features which have an important impact on visual perception from the reference pattern, and then adopt a three-stage approach to synthesize new patterns. The synthesis starts with a randomly generated pattern whose element density is the same as that of the reference pattern, and then we substitutes the elements iteratively to optimize the proportion and neighborhood features. Finally, we iteratively adjust the elements' position to ensure that the distance feature of the target pattern is close to that of the reference one. The method can synthesize most of the stroke patterns with the element distribution from uniform to non-uniform, and from overlapping to non-overlapping
Real-time Rendering of Endless Cloud Animation
(The Eurographics Association, 2011) Iwasaki, Kei; Nishino, Takanori; Dobashi, Yoshinori; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
In this paper, we propose a real-time animation method for dynamic clouds illuminated by sunlight and skylight with multiple scattering. In order to create animations of outdoor scenes, it is necessary to render time-varying dynamic clouds. However, the simulation and the radiance calculation of dynamic clouds are computationally expensive. In order to address this problem, we propose an efficient method to create endless animations of dynamic clouds. The proposed method prepares a database of dynamic clouds consisting of a finite number of volume data. Using this database, volume data for the endless animation is generated at run time using the concept of Video Textures, and this data is rendered in real-time using GPU.
Real-time Realistic Voxel-based Rendering
(The Eurographics Association, 2011) Chang, S.-H.; Lai, Yu-Chi; Niu, Yuzhen; Liu, Feng; Hua, K.-L.; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
With the advance of graphics hardware, setting 3D texture as render target is newly available to allow voxelization algorithms to record the existence, color and normal information in a voxel directly without specific encoding and decoding mechanism. In this paper two new voxel-based applications are proposed to take advantage of this new functionality for interactively rendering realistic lighting effects including shadow of objects with complex occlusion and refraction and transmission of transparent objects. An absorption coefficient is computed according to the number of surface drawing in each voxel during voxelization and used to compute the amount of light passing through partial occluded complex objects. The refraction and transmission of light passing through transparent objects is simulated by our multiple refraction algorithm using surface normal, transmission coefficient and refraction index in each voxel. All these applications can generate the result in real-time without any preprocessing step. Additionally, we also found that the newly available geometry shader can be used to transform a highly complex surface-represented scene into a set of high-resolution voxels in only one GPU pass. This possibly improve the efficiency of the voxelization process.
Two Simple Single-pass GPU methods for Multi-channel Surface Voxelization of Dynamic Scenes
(The Eurographics Association, 2011) Gaitatzes, Athanasios; Mavridis, Pavlos; Papaioannou, Georgios; Bing-Yu Chen and Jan Kautz and Tong-Yee Lee and Ming C. Lin
An increasing number of rendering and geometry processing algorithms relies on volume data to calculate anything from effects like smoke/fluid simulations, visibility information or global illumination effects. We present two real-time and simple-to-implement novel surface voxelization algorithms and a volume data caching structure, the Volume Buffer, which encapsulates functionality, storage and access similar to a frame buffer object, but for threedimensional scalar data. The Volume Buffer can rasterize primitives in 3d space and accumulate up to 1024 bits of arbitrary data per voxel, as required by the specific application. The strength of our methods is the simplicity of the implementation resulting in fast computation times and very easy integration with existing frameworks and rendering engines.
Bokeh Rendering with a Physical Lens
(The Eurographics Association, 2012) Liu, Xin; Rokne, Jon; Chris Bregler and Pedro Sander and Michael Wimmer
Bokeh is important for the realism and aesthetics of graphical rendering, but hard to simulate. In this paper, we propose a novel method that conceptually shoots a 3D display with a physical camera. While a high-quality 3D display is not available, we render the 3D scene layer by layer on a 2D display, and shoot each rendered layer with a physical camera whose focus is adjusted to produce the right amount of blurs. The pure colours and opacities of each layer are extracted by a matting technique and then combined into a single image by alpha blending. The proposed method provides an alternative to bokeh simulation by purely computational algorithms.

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