27-Issue 7

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https://diglib.eg.org/handle/10.2312/140

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Preface, Table of Contents, Cover
(The Eurographics Association and Blackwell Publishing, Inc, 2008)
Real-time Animation of Sand-Water Interaction
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Rungjiratananon, Witawat; Szego, Zoltan; Kanamori, Yoshihiro; Nishita, Tomoyuki
Recent advances in physically-based simulations have made it possible to generate realistic animations. However, in the case of solid-fluid coupling, wetting effects have rarely been noticed despite their visual importance especially in interactions between fluids and granular materials.This paper presents a simple particle-based method to model the physical mechanism of wetness propagating through granular materials; Fluid particles are absorbed in the spaces between the granular particles and these wetted granular particles then stick together due to liquid bridges that are caused by surface tension and which will subsequently disappear when over-wetting occurs. Our method can handle these phenomena by introducing a wetness value for each granular particle and by integrating those aspects of behavior that are dependent on wetness into the simulation framework. Using this method, a GPU-based simulator can achieve highly dynamic animations that include wetting effects in real time.
Smart Motion Synthesis
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Oshita, Masaki
Creating long motion sequences is a time-consuming task even when motion capture equipment or motion editing tools are used. In this paper, we propose a system for creating a long motion sequence by combining elementary motion clips. The user is asked to first input motions on a timeline. The system then automatically generates a continuous and natural motion. Our system employs four motion synthesis methods: motion transition, motion connection, motion adaptation, and motion composition. Based on the constraints between the feet of the animated character and the ground, and the timing of the input motions, the appropriate method is determined for each pair of overlapped or sequential motions. As the user changes the arrangement of the motion clips, the system interactively changes the output motion. Alternatively, the user can make the system execute an input motion as soon as possible so that it follows the previous motion smoothly. Using our system, users can make use of existing motion clips. Because the entire process is automatic, even novices can easily use our system. A prototype system demonstrates the effectiveness of our approach.
Example-based Multiple Local Color Transfer by Strokes
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Wen, Chung-Lin; Hsieh, Chang-Hsi; Chen, Bing-Yu; Ouhyoung, Ming
This paper investigates a new approach for color transfer. Rather than transferring color from one image to another globally, we propose a system with a stroke-based user interface to provide a direct indication mechanism. We further present a multiple local color transfer method. Through our system the user can easily enhance a defect (source) photo by referring to some other good quality (target) images by simply drawing some strokes. Then, the system will perform the multiple local color transfer automatically. The system consists of two major steps. First, the user draws some strokes on the source and target images to indicate corresponding regions and also the regions he or she wants to preserve. The regions to be preserved which will be masked out based on an improved graph cuts algorithm. Second, a multiple local color transfer method is presented to transfer the color from the target image(s) to the source image through gradient-guided pixel-wise color transfer functions. Finally, the defect (source) image can be enhanced seamlessly by multiple local color transfer based on some good quality (target) examples through an interactive and intuitive stroke-based user interface.
Robust and Efficient Wave Simulations on Deforming Meshes
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Angst, Roland; Thuerey, Nils; Botsch, Mario; Gross, Markus
The goal of this paper is to enable the interactive simulation of phenomena such as animated fluid characters. While full 3D fluid solvers achieve this with control algorithms, these 3D simulations are usually too costly for real-time environments. In order to achieve our goal, we reduce the problem from a three- to a two-dimensional one, and make use of the shallow water equations to simulate surface waves that can be solved very efficiently. In addition to a low runtime cost, stability is likewise crucial for interactive applications. Hence, we make use of an implicit time integration scheme to obtain a robust solver. To ensure a low energy dissipation, we apply an Implicit Newmark time integration scheme. We propose a general formulation of the underlying equations that is tailored towards the use with an Implicit Newmark integrator. Furthermore, we gain efficiency by making use of a direct solver. Due to the generality of our formulation, the fluid simulation can be coupled interactively with arbitrary external forces, such as forces caused by inertia or collisions. We will discuss the properties of our algorithm, and demonstrate its robustness with simulations on strongly deforming meshes.
Online Personalised Non-photorealistic Rendering Technique for 3D Geometry from Incremental Sketching
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ku, Daychyi; Qin, Shengfeng; Wright, David K.; Ma, Cuixia
This paper presents an online personalised non-photorealistic rendering (NPR) technique for 3D models generated from interactively sketched input. This technique has been integrated into a sketch-based modelling system. It lets users interact with computers by drawing naturally, without specifying the number, order, or direction of strokes. After sketches are interpreted as 3D objects, they can be rendered with personalised drawing styles so that the reconstructed 3D model can be presented in a sketchy style similar in appearance to what have been drawn for the 3D model. This technique captures the user s drawing style without using template or prior knowledge of the sketching style. The personalised rendering style can be applied to both visible and initially invisible geometry. The rendering strokes are intelligently selected from the input sketches and mapped to edges of the 3D object. In addition, non-geometric information such as surface textures can be added to the recognised object in different sketching modes. This will integrate sketch-based incremental 3D modelling and NPR into conceptual design.
Gradient-based Interpolation and Sampling for Real-time Rendering of Inhomogeneous, Single-scattering Media
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ren, Zhong; Zhou, Kun; Lin, Stephen; Guo, Baining
We present a real-time rendering algorithm for inhomogeneous, single scattering media, where all-frequency shading effects such as glows, light shafts, and volumetric shadows can all be captured. The algorithm first computes source radiance at a small number of sample points in the medium, then interpolates these values at other points in the volume using a gradient-based scheme that is efficiently applied by sample splatting. The sample points are dynamically determined based on a recursive sample splitting procedure that adapts the number and locations of sample points for accurate and efficient reproduction of shading variations in the medium. The entire pipeline can be easily implemented on the GPU to achieve real-time performance for dynamic lighting and scenes. Rendering results of our method are shown to be comparable to those from ray tracing.
Local Volume Preservation for Skinned Characters
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Rohmer, Damien; Hahmann, Stefanie; Cani, Marie-Paule
Generating plausible deformations of a character skin within the standard production pipeline is a challenge. This paper presents a volume preservation method dedicated to skinned characters. As usual, the character is defined by a skin mesh at some rest pose and an animation skeleton. At each animation step, skin deformations are first computed using standard SSD. Our method corrects the result using a set of local deformations which model the fold-over-free, constant volume behavior of soft tissues. This is done geometrically, without the need of any physically-based simulation. To make the method easily applicable, we also provide automatic ways to extract the local regions where volume is to be preserved and to compute adequate skinning weights, both based on the character s morphology.
Perceptual Evaluation of Color-to-Grayscale Image Conversions
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Cadik, M.
Color images often have to be converted to grayscale for reproduction, artistic purposes, or for subsequent processing. Methods performing the conversion of color images to grayscale aim to retain as much information about the original color image as possible, while simultaneously producing perceptually plausible grayscale results. Recently, many methods of conversion have been proposed, but their performance has not yet been assessed. Therefore, the strengths and weaknesses of color-to-grayscale conversions are not known. In this paper, we present the results of two subjective experiments in which a total of 24 color images were converted to grayscale using seven state-of-the-art conversions and evaluated by 119 human subjects using a paired comparison paradigm. We surveyed nearly 20000 human responses and used them to evaluate the accuracy and preference of the color-to-grayscale conversions. To the best of our knowledge, the study presented in this paper is the first perceptual evaluation of color-to-grayscale conversions. Besides exposing the strengths and weaknesses of the researched methods, the aim of the study is to attain a deeper understanding of the examined field, which can accelerate the progress of color-to-grayscale conversion.
Real-Time Depth-of-Field Rendering Using Point Splatting on Per-Pixel Layers
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Lee, Sungkil; Kim, Gerard Jounghyun; Choi, Seungmoon
We present a real-time method for rendering a depth-of-field effect based on the per-pixel layered splatting where source pixels are scattered on one of the three layers of a destination pixel. In addition, the missing information behind foreground objects is filled with an additional image of the areas occluded by nearer objects. The method creates high-quality depth-of-field results even in the presence of partial occlusion, without major artifacts often present in the previous real-time methods. The method can also be applied to simulating defocused highlights. The entire framework is accelerated by GPU, enabling real-time post-processing for both off-line and interactive applications.
Caustic Forecasting: Unbiased Estimation of Caustic Lighting for Global Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Budge, B. C.; Anderson, J. C.; Joy, K. I.
We present an unbiased method for generating caustic lighting using importance sampled Path Tracing with Caustic Forecasting. Our technique is part of a straightforward rendering scheme which extends the Illumination by Weak Singularities method to allow for fully unbiased global illumination with rapid convergence. A photon shooting preprocess, similar to that used in Photon Mapping, generates photons that interact with specular geometry. These photons are then clustered, effectively dividing the scene into regions which will contribute similar amounts of caustic lighting to the image. Finally, the photons are stored into spatial data structures associated with each cluster, and the clusters themselves are organized into a spatial data structure for fast searching. During rendering we use clusters to decide the caustic energy importance of a region, and use the local photons to aid in importance sampling, effectively reducing the number of samples required to capture caustic lighting.
Automatic Facsimile of Chinese Calligraphic Writings
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Xu, Songhua; Jiang, Hao; Jin, Tao; Lau, Francis C.M.; Pan, Yunhe
Progressive Interpolation based on Catmull-Clark Subdivision Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Chen, Zhongxian; Luo, Xiaonan; Tan, Le; Ye, Binghong; Chen, Jiapeng
We introduce a scheme for constructing a Catmull-Clark subdivision surface that interpolates the vertices of a quadrilateral mesh with arbitrary topology. The basic idea here is to progressively modify the vertices of an original mesh to generate a new control mesh whose limit surface interpolates all vertices in the original mesh. The scheme is applicable to meshes with any size and any topology, and it has the advantages of both a local scheme and a global scheme.
Distortion Optimization based Image Completion from a Large Displacement View
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Liu, Chunxiao; Yang, Yingzhen; Peng, Qunsheng; Wang, Jin; Chen, Wei
We present a new image completion method based on an additional large displacement view (LDV) of the same scene for faithfully repairing large missing regions on the target image in an automatic way. A coarse-to-fine distortion correction algorithm is proposed to minimize the perspective distortion in the corresponding parts for the common scene regions on the LDV image. First, under the assumption of a planar scene, the LDV image is warped according to a homography to generate the initial correction result. Second, the residual distortions in the common known scene regions are revealed by means of a mismatch detection mechanism and relaxed by energy optimization of overlap correspondences, with the expectations of color constancy and displacement field smoothness. The fundamental matrix for the two views is then computed based on the reliable correspondence set. Third, under the constraints of epipolar geometry, displacement field smoothness and color consistency of the neighboring pixels, the missing pixels are orderly restored according to a specially defined repairing priority function. We finally eliminate the ghost effect between the repaired region and its surroundings by Poisson image blending. Experimental results demonstrate that our method outperforms recent state-of-the-art image completion methods for repairing large missing area with complex structure information.
Photon-driven Irradiance Cache
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Brouillat, J.; Gautron, P.; Bouatouch, K.
We describe a global illumination method combining two well known techniques: photon mapping and irradiance caching. The photon mapping method has the advantage of being view independent but requires a costly additional rendering pass, called final gathering. As for irradiance caching, it is view-dependent, irradiance is only computed and cached on surfaces of the scene as viewed by a single camera. To compute records covering the entire scene, the irradiance caching method has to be run for many cameras, which takes a long time and is a tedious task since the user has to place the needed cameras manually. Our method exploits the advantages of these two methods and avoids any intervention of the user. It computes a refined, view-independent irradiance cache from a photon map. The global illumination solution is then rendered interactively using radiance cache splatting.
Interactive Global Illumination for Deformable Geometry in CUDA
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Schmitz, Arne; Tavenrath, Markus; Kobbelt, Leif
Interactive global illumination for fully deformable scenes with dynamic relighting is currently a very elusive goal in the area of realistic rendering. In this work we propose a system that is based on explicit visibility calculations and which is highly efficient and scalable. The rendering equation defines the light exchange between surfaces, which we approximate by subsampling. By utilizing the power of modern parallel GPUs using the CUDA framework we achieve interactive frame rates. Since we update the global illumination continuously in an asynchronous fashion, we maintain interactivity at all times for moderately complex scenes. We show that we can achieve higher frame rates for scenes with moving light sources, diffuse indirect illumination and dynamic geometry than other current methods, while maintaining a high image quality.
The Craniofacial Reconstruction from the Local Structural Diversity of Skulls
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Pei, Yuru; Zha, Hongbin; Yuan, Zhongbiao
The craniofacial reconstruction is employed as an initialization of the identification from skulls in forensics. In this paper, we present a two-level craniofacial reconstruction framework based on the local structural diversity of the skulls. On the low level, the holistic reconstruction is formulated as the superimposition of the selected tissue map on the novel skull. The crux is the accurate map registration, which is implemented as a warping guided by the 2D feature curve patterns. The curve pattern extraction under an energy minimization framework is proposed for the automatic feature labeling on the skull depth map. The feature configuration on the warped tissue map is expected to resemble that on the novel skull. In order to make the reconstructed faces personalized, on the high level, the local facial features are estimated from the skull measurements via a RBF model. The RBF model is learnt from a dataset of the skull and the face feature pairs extracted from the head volume data. The experiments demonstrate the facial outlooks can be reconstructed feasibly and efficiently.
A Resolution Independent Approach for the Accurate Rendering of Grooved Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Bosch, C.; Pueyo, X.; Merillou, S.; Ghazanfarpour, D.
This paper presents a method for the accurate rendering of path-based surface details such as grooves, scratches and similar features. The method is based on a continuous representation of the features in texture space, and the rendering is performed by means of two approaches: one for isolated or non-intersecting grooves and another for special situations like intersections or ends. The proposed solutions perform correct antialiasing and take into account visibility and inter-reflections with little computational effort and memory requirements. Compared to anisotropic BRDFs and scratch models, we have no limitations on the distribution of grooves over the surface or their geometry, thus allowing more general patterns. Compared to displacement mapping techniques, we can efficiently simulate features of all sizes without requiring additional geometry or multiple representations.
Sketching MLS Image Deformations On the GPU
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Weng, Yanlin; Shi, Xiaohan; Bao, Hujun; Zhang, Jun
In this paper, we present an image editing tool that allows the user to deform images using a sketch-based interface. The user simply sketches a set of source curves in the input image, and also some target curves that the source curves should be deformed to. Then the moving least squares (MLS) deformation technique [SMW06] is adapted to produce realistic deformations while satisfying the curves positional constraints. We also propose a scheme to reduce image fold-overs in MLS deformations. Our system has a very intuitive user interface, generates physically plausible deformations, and can be easily implemented on the GPU for real-time performance.
Interactive Glossy Reflections using GPU-based Ray Tracing with Adaptive LOD
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Yu, Xuan; Wang, Rui; Yu, Jingyi
We present an interactive GPU-based algorithm for accurately rendering high-quality, dynamic glossy reflection effects from both HDR environment maps and local scene objects. Our method uses hardware rasterization to produce primary pixels, and GPU-based BRDF importance sampling [CK07] to quickly generate reflected rays. We utilize a fast GPU ray tracer proposed by Carr et al. [CHCH06] to compute reflection hits. Our main contribution is an adaptive level-of-detail (LOD) control algorithm that greatly improves ray tracing performance during reflection shading. Specifically, we use the solid angle represented by each reflected ray to adaptively pick the level of termination in the BVH traversal step during ray tracing. This leads to 2 - 3x speedup over an unmodified implementation of [CHCH06]. Based on the same solid angle measure, we derive a texture filtering formula to reduce reflection aliasing artifacts, taking advantage of hardware MIP mapping. This extends the filtering algorithm presented in [CK07] from environment mapping to local scene reflection. Using our algorithm, we demonstrate interactive rendering rates for several scenes featuring dynamic lighting and material changes, spatially varying BRDF parameters, and rigid-body object movement.

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