28-Issue 7

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

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    Affective Modelling: Profiling Geometrical Models with Human Emotional Responses
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Lo, Cheng-Hung; Chu, Chih-Hsing
    In this paper, a novel concept, Affective Modelling, is introduced to encapsulate the idea of creating 3D models based on the emotional responses that they may invoke. Research on perceptually-related issues in Computer Graphics focuses mostly on the rendering aspect. Low-level perceptual criteria taken from established Psychology theories or identified by purposefully-designed experiments are utilised to reduce rendering effort or derive quality evaluation schemes. For modelling, similar ideas have been applied to optimise the level of geometrical details. High-level cognitive responses such as emotions/feelings are less addressed in graphics literatures. This paper investigates the possibility of incorporating emotional/affective factors for 3D model creations. Using a glasses frame model as our test case, we demonstrate a methodological framework to build the links between human emotional responses and geometrical features. We design and carry out a factorial experiment to systematically analyse how certain shape factors individually and interactively influence the viewer s impression of the shape of glasses frames. The findings serve as a basis for establishing computational models that facilitate emotionally-guided 3D modelling.
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    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.
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    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.
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    Curvature Aware Fundamental Cycles
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Diaz-Gutierrez, P.; Eppstein, D.; Gopi, M.
    We present a graph algorithm to find fundamental cycles aligned with the principal curvature directions of a surface. Specifically, we use the tree-cotree decomposition of graphs embedded in manifolds, guided with edge weights, in order to produce these cycles. Our algorithm is very quick compared to existing methods, with a worst case running time of O(n log n+gn) where n is the number of faces and g is the surface genus. Further, its flexibility to accommodate different weighting functions and to handle boundaries may be used to produce cycles suitable for a variety of applications and models.
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    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.
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    Edit Propagation on Bidirectional Texture Functions
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Xu, Kun; Wang, Jiaping; Tong, Xin; Hu, Shi-Min; Guo, Baining
    We propose an efficient method for editing bidirectional texture functions (BTFs) based on edit propagation scheme. In our approach, users specify sparse edits on a certain slice of BTF. An edit propagation scheme is then applied to propagate edits to the whole BTF data. The consistency of the BTF data is maintained by propagating similar edits to points with similar underlying geometry/reflectance. For this purpose, we propose to use view independent features including normals and reflectance features reconstructed from each view to guide the propagation process. We also propose an adaptive sampling scheme for speeding up the propagation process. Since our method needn t any accurate geometry and reflectance information, it allows users to edit complex BTFs with interactive feedback.
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    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.
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    Fast, Sub-pixel Antialiased Shadow Maps
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Pan, Minghao; Wang, Rui; Chen, Weifeng; Zhou, Kun; Bao, Hujun
    Solving aliasing artifacts is an essential problem in shadow mapping approaches. Many works have been proposed, however, most of them focused on removing the texel-level aliasing that results from the limited resolution of shadow maps. Little work has been done to solve the pixel-level shadow aliasing that is produced by the rasterization on the screen plane. In this paper, we propose a fast, sub-pixel antialiased shadowing algorithm to solve the pixel aliasing problem. Our work is based on the alias-free shadow maps, which is capable of computing accurate per-pixel shadow, and only incurs little cost to extend to sub-pixel accuracy. Instead of direct supersampling the screen space, we take facets to approximate pixels in shadow testing. The shadowed area of one facet is rapidly evaluated by projecting blocker geometry onto a supersampled 2D occlusion mask with bitmasks fusion. It provides a sub-pixel occlusion sampling so as to capture fine shadow details and features. Furthermore, we introduce the silhouette mask map that limits visibility evaluation to pixels only on the silhouette, which greatly reduces the computation cost. Our algorithm runs entirely on the GPU, achieving real-time performance and is an order of magnitude faster than the brute-force supersampling method to produce comparable 32x antialiased shadows.
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    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.
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    Frontmatter and Cover
    (The Eurographics Association and Blackwell Publishing Ltd, 2009)
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    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.
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    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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    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.
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    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.
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    Image-to-Geometry Registration: a Mutual Information Method exploiting Illumination-related Geometric Properties
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Corsini, Massimiliano; Dellepiane, Matteo; Ponchio, Federico; Scopigno, Roberto
    This work concerns a novel study in the field of image-to-geometry registration. Our approach takes inspiration from medical imaging, in particular from multi-modal image registration. Most of the algorithms developed in this domain, where the images to register come from different sensors (CT, X-ray, PET), are based on Mutual Information, a statistical measure of non-linear correlation between two data sources. The main idea is to use mutual information as a similarity measure between the image to be registered and renderings of the model geometry, in order to drive the registration in an iterative optimization framework. We demonstrate that some illumination-related geometric properties, such as surface normals, ambient occlusion and reflection directions can be used for this purpose. After a comprehensive analysis of such properties we propose a way to combine these sources of information in order to improve the performance of our automatic registration algorithm. The proposed approach can robustly cover a wide range of real cases and can be easily extended.
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    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.
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    Interactive Rendering of Interior Scenes with Dynamic Environment Illumination
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Yue, Yonghao; Iwasaki, Kei; Chen, Bing-Yu; Dobashi, Yoshinori; Nishita, Tomoyuki
    A rendering system for interior scenes is proposed in this paper. The light reaches the interior scene, usually through small regions, such as windows or abat-jours, which we call portals. To provide a solution, suitable for rendering interior scenes with portals, we extend the traditional precomputed radiance transfer approaches. In our approach, a bounding sphere, which we call a shell, of the interior, centered at each portal, is created and the light transferred from the shell towards the interior through the portal is precomputed. Each shell acts as an environment light source and its intensity distribution is determined by rendering images of the scene, viewed from the center of the shell. By updating the intensity distribution of the shell at each frame, we are able to handle dynamic objects outside the shells. The material of the portals can also be modified at run time (e.g. changing from transparent glass to frosted glass). Several applications are shown, including the illumination of a cathedral, lit by skylight at different times of a day, and a car, running in a town, at interactive frame rates, with a dynamic viewpoint.
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    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.
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    Linkless Octree Using Multi-Level Perfect Hashing
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Choi, Myung Geol; Ju, Eunjung; Chang, Jung-Woo; Lee, Jehee; Kim, Young J.
    The standard C/C++ implementation of a spatial partitioning data structure, such as octree and quadtree, is often inefficient in terms of storage requirements particularly when the memory overhead for maintaining parent-to-child pointers is significant with respect to the amount of actual data in each tree node. In this work, we present a novel data structure that implements uniform spatial partitioning without storing explicit parent-to-child pointer links. Our linkless tree encodes the storage locations of subdivided nodes using perfect hashing while retaining important properties of uniform spatial partitioning trees, such as coarse-to-fine hierarchical representation, efficient storage usage, and efficient random accessibility. We demonstrate the performance of our linkless trees using image compression and path planning examples.
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    Live Video Montage with a Rotating Camera
    (The Eurographics Association and Blackwell Publishing Ltd, 2009) Dong, Zilong; Jiang, Lei; Zhang, Guofeng; Wang, Qing; Bao, Hujun
    High-quality video editing usually requires accurate layer separation in order to resolve occlusions. However, most of the existing bilayer segmentation algorithms require either considerable user intervention or a simple stationary camera configuration with known background, which is difficult to meet for many real world online applications. This paper demonstrates that various visually appealing montage effects can be online created from a live video captured by a rotating camera, by accurately retrieving the camera state and segmenting out the dynamic foreground. The key contribution is that a novel fast bilayer segmentation method is proposed which can effectively extract the dynamic foreground under rotational camera configuration, and is robust to imperfect background estimation and complex background colors. Our system can create a variety of live visual effects, including but not limited to, realistic virtual object insertion, background substitution and blurring, non-photorealistic rendering and camouflage effect. A variety of challenging examples demonstrate the effectiveness of our method.