33-Issue 7

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https://diglib.eg.org/handle/10.2312/11789

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    Multiple Shape Correspondence by Dynamic Programming
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Sahillioglu, Yusuf; Yemez, Yucel; J. Keyser, Y. J. Kim, and P. Wonka
    We present a multiple shape correspondence method based on dynamic programming, that computes consistent bijective maps between all shape pairs in a given collection of initially unmatched shapes. As a fundamental distinction from previous work, our method aims to explicitly minimize the overall distortion, i.e., the average isometric distortion of the resulting maps over all shape pairs. We cast the problem as optimal path finding on a graph structure where vertices are maps between shape extremities. We exploit as much context information as possible using a dynamic programming based algorithm to approximate the optimal solution. Our method generates coarse multiple correspondences between shape extremities, as well as denser correspondences as byproduct. We assess the performance on various mesh sequences of (nearly) isometric shapes. Our experiments show that, for isometric shape collections with non-uniform triangulation and noise, our method can compute relatively dense correspondences reasonably fast and outperform state of the art in terms of accuracy.
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    Fractional Reyes-Style Adaptive Tessellation for Continuous Level of Detail
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Liktor, Gabor; Pan, Minghao; Dachsbacher, Carsten; J. Keyser, Y. J. Kim, and P. Wonka
    In this paper we present a fractional parametric splitting scheme for Reyes-style adaptive tessellation. Our parallel algorithm generates crack-free tessellation from a parametric surface, which is also free of sudden temporal changes under animation. Continuous level of detail is not addressed by existing Reyes-style methods, since these aim to produce subpixel-sized micropolygons, where topology changes are no longer noticeable. Using our method, rendering pipelines that use larger triangles, thus sensitive to geometric popping, may also benefit from the quality of the split-dice tessellation stages of Reyes. We demonstrate results on a real-time GPU implementation, going beyond the limited quality and resolution of the hardware tessellation unit. In contrast to previous split-dice methods, our split stage is compatible with the fractional hardware tessellation scheme that has been designed for continuous level of detail.
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    Realistic Road Path Reconstruction from GIS Data
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Nguyen, Hoang Ha; Desbenoit, Brett; Daniel, Marc; J. Keyser, Y. J. Kim, and P. Wonka
    We introduce a new approach to construct smooth piecewise curves representing realistic road paths. Given a GIS database of road networks in which sampled points are organized in 3D polylines, our method creates horizontal, then vertical curves, and finally combines them to produce 3D road paths. We first estimate the possibility of each point of being a junction between two separate primitive curve segments. Next, we design a tree-traversal algorithm to expand sequences of local best fit primitives which are then merged together with respect to the G1 continuity constraint and civil engineering rules. We apply the Levenberg-Marquardt method to minimize the error between the resulting curve and the sampled points while preserving the G1 continuity.
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    shade.js: Adaptive Material Descriptions
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Sons, Kristian; Klein, Felix; Sutter, Jan; Slusallek, Philipp; J. Keyser, Y. J. Kim, and P. Wonka
    In computer graphics a material is a visual concept that is parameterizable and should work for arbitrary 3D assets and rendering systems. Since provided parameters and attributes as well as the capabilities of rendering systems vary considerably, a material needs to adapt to its execution environment. In current approaches, the adaptation logic is 'baked' into the rendering application based on string manipulation, compiler directives, or metaprogramming facilities. However, in order to achieve application-independent and self-contained material descriptions, the adaptation logic needs to be part of the material description itself. In this paper we present shade.js, a novel material description using a dynamic language to achieve the necessary adaptivity. A shader can inspect its execution environment and adapt to the available parameters and renderer capabilities at run time. Additionally, shade.js exploits the polymorphism that comes with non-explicit declaration of types. These two novel features allow for writing adaptable and thus more general material descriptions. Based on the concrete execution environment at run time, the accompanied compiler generates specialized shader code that is specifically typed and optimized for the target rendering system and algorithm. We evaluate shade.js with examples targeting four different rendering approaches (forward and deferred rasterization, ray-tracing, and global illumination). We show that we can improve convenience and flexibility for specifying materials without sacrificing performance.
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    Incompressible SPH using the Divergence-Free Condition
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Kang, Nahyup; Sagong, Donghoon; J. Keyser, Y. J. Kim, and P. Wonka
    In this paper, we present a novel SPH framework to simulate incompressible fluid that satisfies both the divergencefree condition and the density-invariant condition. In our framework, the two conditions are applied separately. First, the divergence-free condition is enforced when solving the momentum equation. Later, the density-invariant condition is applied after the time integration of the particle positions. Our framework is a purely Lagrangian approach so that no auxiliary grid is required. Compared to the previous density-invariant based SPH methods, the proposed method is more accurate due to the explicit satisfaction of the divergence-free condition. We also propose a modified boundary particle method for handling the free-slip condition. In addition, two simple but effective methods are proposed to reduce the particle clumping artifact induced by the density-invariant condition.
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    Preface and Table of Contents
    (The Eurographics Association and Blackwell Publishing Ltd., 2014) J. Keyser, Y. J. Kim, and P. Wonka
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    Single-shot High Dynamic Range Imaging Using Coded Electronic Shutter
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Cho, Hojin; Kim, Seon Joo; Lee, Seungyong; J. Keyser, Y. J. Kim, and P. Wonka
    Typical high dynamic range (HDR) imaging approaches based on multiple images have difficulties in handling moving objects and camera shakes, suffering from the ghosting effect and the loss of sharpness in the output HDR image. While there exist a variety of solutions for resolving such limitations, most of the existing algorithms are susceptible to complex motions, saturation, and occlusions. In this paper, we propose an HDR imaging approach using the coded electronic shutter which can capture a scene with row-wise varying exposures in a single image. Our approach enables a direct extension of the dynamic range of the captured image without using multiple images, by photometrically calibrating rows with different exposures. Due to the concurrent capture of multiple exposures, misalignments of moving objects are naturally avoided with significant reduction in the ghosting effect. To handle the issues with under-/over-exposure, noise, and blurs, we present a coherent HDR imaging process where the problems are resolved one by one at each step. Experimental results with real photographs, captured using a coded electronic shutter, demonstrate that our method produces a high quality HDR images without the ghosting and blur artifacts.
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    Real-Time Symmetry-Preserving Deformation
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Wu, Xiaokun; Wand, Michael; Hildebrandt, Klaus; Kohli, Pushmeet; Seidel, Hans-Peter; J. Keyser, Y. J. Kim, and P. Wonka
    In this paper, we address the problem of structure-aware shape deformation: We specifically consider deformations that preserve symmetries of the shape being edited. While this is an elegant approach for obtaining plausible shape variations from minimal assumptions, a straightforward optimization is numerically expensive and poorly conditioned. Our paper introduces an explicit construction of bases of linear spaces of shape deformations that exactly preserve symmetries for any user-defined level of detail. This permits the construction of low-dimensional spaces of low-frequency deformations that preserve the symmetries. We obtain substantial speed-ups over alternative approaches for symmetry-preserving shape editing due to (i) the sub-space approach, which permits low-res editing, (ii) the removal of redundant, symmetric information, and (iii) the simplification of the numerical formulation due to hard-coded symmetry preservation. We demonstrate the utility in practice by applying our framework to symmetry-preserving co-rotated iterative Laplace surface editing of models with complex symmetry structure, including partial and nested symmetry.
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    Learning Natural Colors for Image Recoloring
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Huang, Hao-Zhi; Zhang, Song-Hai; Martin, Ralph R.; Hu, Shi-Min; J. Keyser, Y. J. Kim, and P. Wonka
    We present a data-driven method for automatically recoloring a photo to enhance its appearance or change a viewer's emotional response to it. A compact representation called a RegionNet summarizes color and geometric features of image regions, and geometric relationships between them. Correlations between color property distributions and geometric features of regions are learned from a database of well-colored photos. A probabilistic factor graph model is used to summarize distributions of color properties and generate an overall probability distribution for color suggestions. Given a new input image, we can generate multiple recolored results which unlike previous automatic results, are both natural and artistic, and compatible with their spatial arrangements.
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    Adaptive Multi-scale Analysis for Point-based Surface Editing
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Nader, Georges; Guennebaud, Gael; Mellado, Nicolas; J. Keyser, Y. J. Kim, and P. Wonka
    This paper presents a tool that enables the direct editing of surface features in large point-clouds or meshes. This is made possible by a novel multi-scale analysis of unstructured point-clouds that automatically extracts the number of relevant features together with their respective scale all over the surface. Then, combining this ingredient with an adequate multi-scale decomposition allows us to directly enhance or reduce each feature in an independent manner. Our feature extraction is based on the analysis of the scale-variations of locally fitted surface primitives combined with unsupervised learning techniques. Our tool may be applied either globally or locally, and millions of points are handled in real-time. The resulting system enables users to accurately edit complex geometries with minimal interaction.
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    Sub-Pixel Anti-Aliasing Via Triangle-Based Geometry Reconstruction
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Du, Wenjun; Feng, Jieqing; Yang, Baoguang; J. Keyser, Y. J. Kim, and P. Wonka
    Anti-aliasing has recently been employed as a post-processing step to adapt to the deferred shading technique in real-time applications. Some of these existing algorithms store supersampling geometric information as geometric buffer (G-buffer) to detect and alleviate sub-pixel-level aliasing artifacts. However, the anti-aliasing filter based on sampled sub-pixel geometries only may introduce unfaithful shading information to the sub-pixel color in uniform-geometry regions, and large G-buffer will increase memory storage and fetch overheads. In this paper, we present a new Triangle-based Geometry Anti-Aliasing (TGAA) algorithm, to address these problems. The coverage triangle of each screen pixel is accessed, and then, the coverage information between the triangle and neighboring sub-pixels is stored in a screen-resolution bitmask, which allows the geometric information to be stored and accessed in an inexpensive manner. Using triangle-based geometry, TGAA can exclude irrelevant neighboring shading samples and achieve faithful anti-aliasing filtering. In addition, a morphological method of estimating the geometric edges in high-frequency geometry is incorporated into the TGAA's anti-aliasing filter to complement the algorithm. The implementation results demonstrate that the algorithm is efficient and scalable for generating high-quality anti-aliased images.
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    Perceptually-motivated Stereoscopic Film Grain
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Templin, Krzysztof; Didyk, Piotr; Myszkowski, Karol; Seidel, Hans-Peter; J. Keyser, Y. J. Kim, and P. Wonka
    Independent management of film grain in each view of a stereoscopic video can lead to visual discomfort. The existing alternative is to project the grain onto the scene geometry. Such grain, however, looks unnatural, changes object perception, and emphasizes inaccuracies in depth arising during 2D-to-3D conversion. We propose an advanced method of grain positioning that scatters the grain in the scene space. In a series of perceptual experiments, we estimate the optimal parameter values for the proposed method, analyze the user preference distribution among the proposed and the two existing methods, and show influence of the method on the object perception.
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    Fast Feature-Oriented Visual Connection for Large Image Collections
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Yan, Qingan; Xu, Zhan; Xiao, Chunxia; J. Keyser, Y. J. Kim, and P. Wonka
    Deriving the visual connectivity across large image collections is a computationally expensive task. Different from current image-oriented match graph construction methods which build on pairwise image matching, we present a novel and scalable feature-oriented image matching algorithm for large collections. Our method improves the match graph construction procedure in three ways. First, instead of building trees repeatedly, we put the feature points of the input image collection into a single kd-tree and select the leaves as our anchor points. Then we construct an anchor graph from which each feature can intelligently find a small portion of related candidates to match. Finally, we design a new form of adjacency matrix for fast feature similarity measuring, and return all the matches in different photos across the whole dataset directly. Experiments show that our feature-oriented correspondence algorithm can explore visual connectivity between images with significant improvement in speed.
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    Advanced Hybrid Particle-Grid Method with Sub-Grid Particle Correction
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Um, Kiwon; Baek, Seungho; Han, JungHyun; J. Keyser, Y. J. Kim, and P. Wonka
    This paper proposes a novel hybrid particle-grid approach to liquid simulation, which uses the fluid-implicitparticle (FLIP) method to resolve the liquid motion and a grid-based particle correction method to complement FLIP. The correction process addresses the high-frequency errors in FLIP ensuring that the particles are properly distributed. The proposed approach enables the corrective procedure to avoid directly processing the particle relationships and supports flexible corrective forces. The proposed technique effectively and efficiently improves the distribution of the particles and therefore enhances the overall simulation quality. The experimental results confirm that the technique is able to conserve the liquid volume and to produce dynamic surface motions, thin liquid sheets, and smooth surfaces without disturbing artifacts such as bumpy noise.
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    Environment-Adaptive Contact Poses for Virtual Characters
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Kang, Changgu; Lee, Sung-Hee; J. Keyser, Y. J. Kim, and P. Wonka
    We present a novel method to generate a virtual character's multi-contact poses adaptive to the various shapes of the environment. Given the user-specified center of mass (CoM) position and direction as inputs, our method finds the potential contacts for the character in the surrounding geometry of the environment and generates a set of stable poses that are contact-rich. Major contributions of the work are in efficiently finding admissible support points for the target environment by precomputing candidate support points from a human pose database, and in automatically generating interactive poses that can maintain stable equilibrium. We develop the concept of support complexity to scale the set of precomputed support points by the geometric complexity of the environment. We demonstrate the effectiveness of our method by creating contact poses for various test cases of environments.
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    Hybrid Particle-grid Modeling for Multi-scale Droplet/Spray Simulation
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Yang, Lipeng; Li, Shuai; Hao, Aimin; Qin, Hong; J. Keyser, Y. J. Kim, and P. Wonka
    This paper presents a novel hybrid particle-grid method that tightly couples Lagrangian particle approach with Eulerian grid approach to simulate multi-scale diffuse materials varying from disperse droplets to dissipating spray and their natural mixture and transition, originated from a violent (high-speed) liquid stream. Despite the fact that Lagrangian particles are widely employed for representing individual droplets and Eulerian grid-based method is ideal for volumetric spray modeling, using either one alone has encountered tremendous difficulties when effectively simulating droplet/spray mixture phenomena with high fidelity. To ameliorate, we propose a new hybrid model to tackle such challenges with many novel technical elements. At the geometric level, we employ the particle and density field to represent droplet and spray respectively, modeling their creation from liquid as well as their seamless transition. At the physical level, we introduce a drag force model to couple droplets and spray, and specifically, we employ Eulerian method to model the interaction among droplets and marry it with the widelyused Lagrangian model. Moreover, we implement our entire hybrid model on CUDA to guarantee the interactive performance for high-effective physics-based graphics applications. The comprehensive experiments have shown that our hybrid approach takes advantages of both particle and grid methods, with convincing graphics effects for disperse droplets and spray simulation.
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    Time-Lapse Photometric Stereo and Applications
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Shen, Fangyang; Sunkavalli, Kalyan; Bonneel, Nicolas; Rusinkiewicz, Szymon; Pfister, Hanspeter; Tong, Xin; J. Keyser, Y. J. Kim, and P. Wonka
    This paper presents a technique to recover geometry from time-lapse sequences of outdoor scenes. We build upon photometric stereo techniques to recover approximate shadowing, shading and normal components allowing us to alter the material and normals of the scene. Previous work in analyzing such images has faced two fundamental difficulties: 1. the illumination in outdoor images consists of time-varying sunlight and skylight, and 2. the motion of the sun is restricted to a near-planar arc through the sky, making surface normal recovery unstable. We develop methods to estimate the reflection component due to skylight illumination. We also show that sunlight directions are usually non-planar, thus making surface normal recovery possible. This allows us to estimate approximate surface normals for outdoor scenes using a single day of data. We demonstrate the use of these surface normals for a number of image editing applications including reflectance, lighting, and normal editing.
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    Fast and Scalable Mesh Superfacets
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Simari, Patricio; Picciau, Giulia; Floriani, Leila De; J. Keyser, Y. J. Kim, and P. Wonka
    In the field of computer vision, the introduction of a low-level preprocessing step to oversegment images into superpixels - relatively small regions whose boundaries agree with those of the semantic entities in the scene - has enabled advances in segmentation by reducing the number of elements to be labeled from hundreds of thousands, or millions, to a just few hundred. While some recent works in mesh processing have used an analogous oversegmentation, they were not intended to be general and have relied on graph cut techniques that do not scale to current mesh sizes. Here, we present an iterative superfacet algorithm and introduce adaptations of undersegmentation error and compactness, which are well-motivated and principled metrics from the vision community. We demonstrate that our approach produces results comparable to those of the normalized cuts algorithm when evaluated on the Princeton Segmentation Benchmark, while requiring orders of magnitude less time and memory and easily scaling to, and enabling the processing of, much larger meshes.
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    Efficient Depth Propagation for Constructing a Layered Depth Image from a Single Image
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Iizuka, Satoshi; Endo, Yuki; Kanamori, Yoshihiro; Mitani, Jun; Fukui, Yukio; J. Keyser, Y. J. Kim, and P. Wonka
    In this paper, we propose an interactive technique for constructing a 3D scene via sparse user inputs. We represent a 3D scene in the form of a Layered Depth Image (LDI) which is composed of a foreground layer and a background layer, and each layer has a corresponding texture and depth map. Given user-specified sparse depth inputs, depth maps are computed based on superpixels using interpolation with geodesic-distance weighting and an optimization framework. This computation is done immediately, which allows the user to edit the LDI interactively. Additionally, our technique automatically estimates depth and texture in occluded regions using the depth discontinuity. In our interface, the user paints strokes on the 3D model directly. The drawn strokes serve as 3D handles with which the user can pull out or push the 3D surface easily and intuitively with real-time feedback. We show our technique enables efficient modeling of LDI that produce sufficient 3D effects.
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    Structure Aware Visual Cryptography
    (The Eurographics Association and John Wiley and Sons Ltd., 2014) Liu, Bin; Martin, Ralph R.; Huang, Ji-Wu; Hu, Shi-Min; J. Keyser, Y. J. Kim, and P. Wonka
    Visual cryptography is an encryption technique that hides a secret image by distributing it between some shared images made up of seemingly random black-and-white pixels. Extended visual cryptography (EVC) goes further in that the shared images instead represent meaningful binary pictures. The original approach to EVC suffered from low contrast, so later papers considered how to improve the visual quality of the results by enhancing contrast of the shared images. This work further improves the appearance of the shared images by preserving edge structures within them using a framework of dithering followed by a detail recovery operation.We are also careful to suppress noise in smooth areas.