28-Issue 7

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https://diglib.eg.org/handle/10.2312/149

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Texture Splicing
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Liu, Yiming; Wang, Jiaping; Xue, Su; Tong, Xin; Kang, Sing Bing; Guo, Baining
We propose a new texture editing operation called texture splicing. For this operation, we regard a texture as having repetitive elements (textons) seamlessly distributed in a particular pattern. Taking two textures as input, texture splicing generates a new texture by selecting the texton appearance from one texture and distribution from the other. Texture splicing involves self-similarity search to extract the distribution, distribution warping, context-dependent warping, and finally, texture refinement to preserve overall appearance. We show a variety of results to illustrate this operation.
Expression Synthesis and Transfer in Parameter Spaces
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Shin, Hyun Joon; Lee, Yunjin
In this paper, we introduce a novel framework that allows users to synthesize the expression of a 3D character by providing a intuitive set of parametric controls. Assuming that human face movements are formed by a set of basis actuation, we analyze a set of real expressions to extract this set together with skin deformation due to the actuation of face. To do this, we first decompose the movement of each marker into a set of distinctive movements. Independent component analysis technique is then adopted to find a independent set of actuations. Our simple and efficient skin deformation model are learned to reproduce the realistic movements of facial parts due to the actuations. In this framework, users can animate characters faces by controlling the amount actuation or by directly manipulating the face geometry. In addition, the proposed method can be applied to expression transfer which reproduces one character s expression in another character s face. Experimental results demonstrate that our method can produce realistic expression efficiently.
An Intuitive Interface for Interactive High Quality Image-Based Modeling
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Habbecke, Martin; Kobbelt, Leif
We present the design of an interactive image-based modeling tool that enables a user to quickly generate detailed 3D models with texture from a set of calibrated input images. Our main contribution is an intuitive user interface that is entirely based on simple 2D painting operations and does not require any technical expertise by the user or difficult pre-processing of the input images. One central component of our tool is a GPU-based multi-view stereo reconstruction scheme, which is implemented by an incremental algorithm, that runs in the background during user interaction so that the user does not notice any significant response delay.
Mesh Segmentation Refinement
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Kaplansky, Lotan; Tal, Ayellet
This paper proposes a method for refining existing mesh segmentations, employing a novel extension of the active contour approach to meshes. Given a segmentation, produced either by an automatic segmentation method or interactively, our algorithm propagates the segment boundaries to more appropriate locations. In addition, unlike most segmentation algorithms, our method allows the boundaries to pass through the mesh faces, resulting in smoother curves, particularly visible on coarse meshes. The method is also capable of changing the number of segments, by enabling splitting and merging of boundary curves during the process. Finally, by changing the propagation rules, it is possible to segment the mesh by a variety of criteria, for instance geometric-meaningful segmentations, texture-based segmentations, or constriction-based segmentations.
Procedural Generation of Rock Piles using Aperiodic Tiling
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Peytavie, A.; Galin, E.; Grosjean, J.; Merillou, S.
In this paper, we present a tiling method for generating piles of rocks without any computationally demanding physically-based simulation. Previous techniques rely on a periodic tiling of rocks and generate unrealistic repetitive patterns. In contrast, our approach relies on a modified corner cube algorithm to generate a set of aperiodic tiles. We generalize the construction method so that the geometry of rocks should straddle corner cubes with a view to avoiding unrealistic gaps in the arrangement of rocks. Moreover, we propose an original technique to control the shape of rocks into contact by computing the Voronoi cells using a parameterized anisotropic distance. Our method has been successfully used to generate landscapes and stone huts and walls with thousands of rocks piled together.
Automatic Correction of Saturated Regions in Photographs using Cross-Channel Correlation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Masood, Syed Z.; Zhu, Jiejie; Tappen, Marshall F.
Incorrectly setting the camera s exposure can have a significant negative effect on a photograph. Over-exposing photographs causes pixels to exhibit unpleasant artifacts due to saturation of the sensor. Saturation removal typically involves user intervention to adjust the color values, which is tedious and time-consuming. This paper discusses how saturation can be automatically removed without compromising the essential details of the image. Our method is based on a smoothness prior: neighboring pixels have similar channel ratios and color values. We demonstrate that high quality saturation-free photos can be obtained from a simple but effective approach.
Procedural Synthesis using Vortex Particle Method for Fluid Simulation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Yoon, Jong-Chul; Kam, Hyeong Ryeol; Hong, Jeong-Mo; Kang, Shin Jin; Kim, Chang-Hun
We propose a fast and effective technique to improve sub-grid visual details of the grid based fluid simulation. Our method procedurally synthesizes the flow fields coming from the incompressible Navier-Stokes solver and the vorticity fields generated by vortex particle method for sub-grid turbulence. We are able to efficiently animate smoke which is highly turbulent and swirling with small scale details. Since this technique does not solve the linear system in high-resolution grids, it can perform fluid simulation more rapidly. We can easily estimate the influence of turbulent and swirling effect to the fluid flow.
ProcDef: Local-to-global Deformation for Skeleton-free Character Animation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ijiri, Takashi; Takayama, Kenshi; Yokota, Hideo; Igarashi, Takeo
Animations of characters with flexible bodies such as jellyfish, snails, and, hearts are difficult to design using traditional skeleton-based approaches. A standard approach is keyframing, but adjusting the shape of the flexible body for each key frame is tedious. In addition, the character cannot dynamically adjust its motion to respond to the environment or user input. This paper introduces a new procedural deformation framework (ProcDef) for designing and driving animations of such flexible objects. Our approach is to synthesize global motions procedurally by integrating local deformations. ProcDef provides an efficient design scheme for local deformation patterns; the user can control the orientation and magnitude of local deformations as well as the propagation of deformation signals by specifying line charts and volumetric fields. We also present a fast and robust deformation algorithm based on shape-matching dynamics and show some example animations to illustrate the feasibility of our framework.
Flow-Based Automatic Generation of Hybrid Picture Mazes
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Wong, Fernando J.; Takahashi, Shigeo
A method for automatically generating a picture maze from two different images is introduced throughout this paper. The process begins with the extraction of salient contours and edge tangent flow information from the primary image in order to build the overall maze. Thus, mazes with passages flowing in the main edge directions and walls that effectively represent an abstract version of the primary image can be successfully created. Furthermore, our proposed approach makes possible the use of their solution path as a means of illustrating the main features of the secondary image, while attempting to keep its image motif concealed until the maze has been finally solved. The contour features and intensity of the secondary image are also incorporated into our method in order to determine the areas of the maze to be shaded by allowing the solution path to go through them. Moreover, an experiment has been conducted to confirm that solution paths can be successfully hidden from the participants in the mazes generated using our method.
Image and Video Abstraction by Anisotropic Kuwahara Filtering
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Kyprianidis, Jan Eric; Kang, Henry; Doellner, Juergen
We present a non-photorealistic rendering technique to transform color images and videos into painterly abstractions. It is based on a generalization of the Kuwahara filter that is adapted to the local shape of features, derived from the smoothed structure tensor. Contrary to conventional edge-preserving filters, our filter generates a painting-like flattening effect along the local feature directions while preserving shape boundaries. As opposed to conventional painting algorithms, it produces temporally coherent video abstraction without extra processing. The GPU implementation of our method processes video in real-time. The results have the clearness of cartoon illustrations but also exhibit directional information as found in oil paintings.
Optimizing Structure Preserving Embedded Deformation for Resizing Images and Vector Art
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Huang, Qi-xing; Mech, Radomir; Carr, Nathan
Smart deformation and warping tools play an important part in modern day geometric modeling systems. They allow existing content to be stretched or scaled while preserving visually salient information. To date, these techniques have primarily focused on preserving local shape details, not taking into account important global structures such as symmetry and line features. In this work we present a novel framework that can be used to preserve the global structure in images and vector art. Such structures include symmetries and the spatial relations in shapes and line features in an image. Central to our method is a new formulation of preserving structure as an optimization problem. We use novel optimization strategies to achieve the interactive performance required by modern day modeling applications. We demonstrate the effectiveness of our framework by performing structure preservation deformation of images and complex vector art at interactive rates.
Approximate on-Surface Distance Computation using Quasi-Developable Charts
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Torchelsen, Rafael P.; Pinto, Francisco; Bastos, Rui; Comba, Joao L. D.
There is a vast number of applications that require distance field computation over triangular meshes. State-of-the-art algorithms have quadratic or sub-quadratic worst-case complexity, making them impractical for interactive applications. While most of the research on this subject has been focused on reducing the computation complexity of the algorithms, in this work we propose an approximate algorithm that achieves similar results working in lower resolutions of the input meshes. The creation of lower resolution meshes is the essence of our proposal. The idea is to identify regions on the input mesh that can be unfolded into planar regions with minimal area distortion (i.e. quasi-developable charts). Once charts are computed, their interior is re-triangulated to reduce the number of triangles, which results in a collection of simplified charts that we call a base mesh. Due to the properties of quasi-developable regions, we are able to compute distance fields over the base mesh instead of over the input mesh. This reduces the memory footprint and data processed for distance computations, which is the bottleneck of these algorithms. We present results that are one order of magnitude faster than current exact solutions, with low approximation errors.
The Dual-microfacet Model for Capturing Thin Transparent Slabs
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Dai, Qiang; Wang, Jiaping; Liu, Yiming; Snyder, John; Wu, Enhua; Guo, Baining
We present a new model, called the dual-microfacet, for those materials such as paper and plastic formed by a thin, transparent slab lying between two surfaces of spatially varying roughness. Light transmission through the slab is represented by a microfacet-based BTDF which tabulates the microfacet s normal distribution (NDF) as a function of surface location. Though the material is bounded by two surfaces of different roughness, we approximate light transmission through it by a virtual slab determined by a single spatially-varying NDF. This enables efficient capturing of spatially variant transparent slices. We describe a device for measuring this model over a flat sample by shining light from a CRT behind it and capturing a sequence of images from a single view. Our method captures both angular and spatial variation in the BTDF and provides a good match to measured materials.
A Shape-Preserving Approach to Image Resizing
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Zhang, Guo-Xin; Cheng, Ming-Ming; Hu, Shi-Min; Martin, Ralph R.
We present a novel image resizing method which attempts to ensure that important local regions undergo a geometric similarity transformation, and at the same time, to preserve image edge structure. To accomplish this, we define handles to describe both local regions and image edges, and assign a weight for each handle based on an importance map for the source image. Inspired by conformal energy, which is widely used in geometry processing, we construct a novel quadratic distortion energy to measure the shape distortion for each handle. The resizing result is obtained by minimizing the weighted sum of the quadratic distortion energies of all handles. Compared to previous methods, our method allows distortion to be diffused better in all directions, and important image edges are well-preserved. The method is efficient, and offers a closed form solution.
Interactive Cover Design Considering Physical Constraints
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Igarashi, Yuki; Igarashi, Takeo; Suzuki, Hiromasa
We developed an interactive system to design a customized cover for a given three-dimensional (3D) object such as a camera, teapot, or car. The system first computes the convex hull of the input geometry. The user segments it into several cloth patches by drawing on the 3D surface. This paper provides two technical contributions. First, it introduces a specialized flattening algorithm for cover patches. It makes each two-dimensional edge in the flattened pattern equal to or longer than the original 3D edge; a smaller patch would fail to cover the object, and a larger patch would result in extra wrinkles. Second, it introduces a mechanism to verify that the user-specified opening would be large enough for the object to be removed. Starting with the initial configuration, the system virtually pulls the object out of the cover while avoiding excessive stretching of cloth patches. We used the system to design real covers and confirmed that it functions as intended.
SecondSkin: An interactive method for appearance transfer
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Van Den Hengely, A.; Sale, D.; Dick, A. R.
SecondSkin estimates an appearance model for an object visible in a video sequence, without the need for complex interaction or any calibration apparatus. This model can then be transferred to other objects, allowing a non-expert user to insert a synthetic object into a real video sequence so that its appearance matches that of an existing object, and changes appropriately throughout the sequence. As the method does not require any prior knowledge about the scene, the lighting conditions, or the camera, it is applicable to video which was not captured with this purpose in mind. However, this lack of prior knowledge precludes the recovery of separate lighting and surface reflectance information. The SecondSkin appearance model therefore combines these factors. The appearance model does require a dominant light-source direction, which we estimate via a novel process involving a small amount of user interaction. The resulting model estimate provides exactly the information required to transfer the appearance of the original object to new geometry composited into the same video sequence.
Variational Surface Approximation and Model Selection
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Li, Bao; Schnabel, Ruwen; Jin, Shiyao; Klein, Reinhard
We consider the problem of approximating an arbitrary generic surface with a given set of simple surface primitives. In contrast to previous approaches based on variational surface approximation, which are primarily concerned with finding an optimal partitioning of the input geometry, we propose to integrate a model selection step into the algorithm in order to also optimize the type of primitive for each proxy. Our method is a joint global optimization of both the partitioning of the input surface as well as the types and number of used shape proxies. Thus, our method performs an automatic trade-off between representation complexity and approximation error without relying on a user supplied predetermined number of shape proxies. This way concise surface representations are found that better exploit the full approximative power of the employed primitive types.
Generalized Discrete Ricci Flow
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Yang, Yong-Liang; Guo, Ren; Luo, Feng; Hu, Shi-Min; Gu, Xianfeng
Surface Ricci flow is a powerful tool to design Riemannian metrics by user defined curvatures. Discrete surface Ricci flow has been broadly applied for surface parameterization, shape analysis, and computational topology. Conventional discrete Ricci flow has limitations. For meshes with low quality triangulations, if high conformality is required, the flow may get stuck at the local optimum of the Ricci energy. If convergence to the global optimum is enforced, the conformality may be sacrificed.This work introduces a novel method to generalize the traditional discrete Ricci flow. The generalized Ricci flow is more flexible, more robust and conformal for meshes with low quality triangulations. Conventional method is based on circle packing, which requires two circles on an edge intersect each other at an acute angle. Generalized method allows the two circles either intersect or separate from each other. This greatly improves the flexibility and robustness of the method. Furthermore, the generalized Ricci flow preserves the convexity of the Ricci energy, this ensures the uniqueness of the global optimum. Therefore the algorithm won t get stuck at the local optimum.Generalized discrete Ricci flow algorithms are explained in details for triangle meshes with both Euclidean and hyperbolic background geometries. Its advantages are demonstrated by theoretic proofs and practical applications in graphics, especially surface parameterization.
HPCCD: Hybrid Parallel Continuous Collision Detection using CPUs and GPUs
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Kim, Duksu; Heo, Jae-Pil; Huh, Jaehyuk; Kim, John; Yoon, Sung-eui
We present a novel, hybrid parallel continuous collision detection (HPCCD) method that exploits the availability of multi-core CPU and GPU architectures. HPCCD is based on a bounding volume hierarchy (BVH) and selectively performs lazy reconstructions. Our method works with a wide variety of deforming models and supports self-collision detection. HPCCD takes advantage of hybrid multi-core architectures - using the general-purpose CPUs to perform the BVH traversal and culling while GPUs are used to perform elementary tests that reduce to solving cubic equations. We propose a novel task decomposition method that leads to a lock-free parallel algorithm in the main loop of our BVH-based collision detection to create a highly scalable algorithm. By exploiting the availability of hybrid, multi-core CPU and GPU architectures, our proposed method achieves more than an order of magnitude improvement in performance using four CPU-cores and two GPUs, compared to using a single CPU-core. This improvement results in an interactive performance, up to 148 fps, for various deforming benchmarks consisting of tens or hundreds of thousand triangles.
Gradient-Preserving Color Transfer
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Xiao, Xuezhong; Ma, Lizhuang
Color transfer is an image processing technique which can produce a new image combining one source image s contents with another image s color style. While being able to produce convincing results, however, Reinhard et al. s pioneering work has two problems-mixing up of colors in different regions and the fidelity problem. Many local color transfer algorithms have been proposed to resolve the first problem, but the second problem was paid few attentions.In this paper, a novel color transfer algorithm is presented to resolve the fidelity problem of color transfer in terms of scene details and colors. It s well known that human visual system is more sensitive to local intensity differences than to intensity itself. We thus consider that preserving the color gradient is necessary for scene fidelity. We formulate the color transfer problem as an optimization problem and solve it in two steps-histogram matching and a gradient-preserving optimization. Following the idea of the fidelity in terms of color and gradient, we also propose a metric for objectively evaluating the performance of example-based color transfer algorithms. The experimental results show the validity and high fidelity of our algorithm and that it can be used to deal with local color transfer.

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