27-Issue 7

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

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A Biorthogonal Wavelet Approach based on Dual Subdivision
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Zhang, Hui; Qin, Guiming; Qin, Kaihuai; Sun, Hanqiu
In this paper a biorthogonal wavelet approach based on Doo-Sabin subdivision is presented. In the dual subdivision like Doo-Sabin scheme, all the old control vertices disappear after one subdivision step, which is a big challenge to the biorthogonal wavelet construction. In our approach, the barycenters of the V-faces corresponding to the old vertices are selected as the vertices associated with the scaling functions to construct the scaling space. The lifting scheme is used to guarantee the fitting quality of the wavelet transform, and a local orthogonalization is introduced with a discrete inner product operation to improve the computation efficiency. Sharp feature modeling based on extended Doo-Sabin subdivision rules is also discussed in the framework of our wavelet construction. The presented wavelet construction is proven to be stable and effective by the experimental results.
A Prism-Free Method for Silhouette Rendering in Inverse Displacement Mapping
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Chen, Ying-Chieh; Chang, Chun-Fa
Silhouette is a key feature that distinguishes displacement mapping from normal mapping. However the silhouette rendering in the GPU implementation of displacement mapping (which is often called inversed displacement mapping) is tricky. Previous approaches rely mostly on construction of additional extruding prism-like geometry, which slows down the rendering significantly. In this paper, we proposed a method for solving the silhouette rendering problem in inverse displace mapping without using any extruding prism-like geometry. At each step of intersection finding, we continuously bends the viewing ray according to the current local tangent space associated with the surface. Thus, it allows mapping a displacement map onto an arbitrary curved surface with more accurate silhouette. While our method is simple, it offers surprisingly good results over Curved Relief Map (CRM) [OP05] in many difficult or degenerated cases.
Reconstructing 3D Shape, Albedo and Illumination from a Single Face Image
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Wang, S. F.; Lai, S. H.
The morphable model has been employed to efficiently describe 3D face shape and the associated albedo with a reduced set of basis vectors. The spherical harmonics (SH) model provides a compact basis to well approximate the image appearance of a Lambertian object under different illumination conditions. Recently, the SH and morphable models have been integrated for 3D face shape reconstruction. However, the reconstructed 3D shape is either inconsistent with the SH bases or obtained just from landmarks only. In this work, we propose a geometrically consistent algorithm to reconstruct the 3D face shape and the associated albedo from a single face image iteratively by combining the morphable model and the SH model. The reconstructed 3D face geometry can uniquely determine the SH bases, therefore the optimal 3D face model can be obtained by minimizing the error between the input face image and a linear combination of the associated SH bases. In this way, we are able to preserve the consistency between the 3D geometry and the SH model, thus refining the 3D shape reconstruction recursively. Furthermore, we present a novel approach to recover the illumination condition from the estimated weighting vector for the SH bases in a constrained optimization formulation independent of the 3D geometry. Experimental results show the effectiveness and accuracy of the proposed face reconstruction and illumination estimation algorithm under different face poses and multiple-light-source illumination conditions.
Interpolatory and Mixed Loop Schemes
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Shi, Zhuo; Lin, Shujin; Luo, Xiaonan; Wang, Renhong
This paper presents a new interpolatory Loop scheme and an unified and mixed interpolatory and approximation subdivision scheme for triangular meshes. The former which is C1 continuous as same as the modified Butterfly scheme has better effect in some complex models. The latter can be used to solve the popping effect problem when switching between meshes at different levels of resolution. The scheme generates surfaces coincident with the Loop subdivision scheme in the limit condition having the coefficient k equal 0. When k equal 1, it will be changed into a new interpolatory subdivision scheme. Eigen-structure analysis demonstrates that subdivision surfaces generated using the new scheme are C1 continuous. All these are achieved only by changing the value of a parameter k. The method is a completely simple one without constructing and solving equations. It can achieve local interpolation and solve the popping effect problem which are the method s advantages over the modified Butterfly scheme.
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.
A Hidden-picture Puzzles Generator
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Yoon, Jong-Chul; Lee, In-Kwon; Kang, Henry
A hidden-picture puzzle contains objects hidden in a background image, in such a way that each object fits closely into a local region of the background. Our system converts image of the background and objects into line drawing, and then finds places in which to hide transformed versions of the objects using rotation-invariant shape context matching. During the hiding process, each object is subjected to a slight deformation to enhance its similarity to the background. The results were assessed by a panel of puzzle-solvers.
Shrinkability Maps for Content-Aware Video Resizing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Zhang, Yi-Fei; Hu, Shi-Min; Martin, Ralph R.
A novel method is given for content-aware video resizing, i.e. targeting video to a new resolution (which may involve aspect ratio change) from the original.We precompute a per-pixel cumulative shrinkability map which takes into account both the importance of each pixel and the need for continuity in the resized result. (If both x and y resizing are required, two separate shrinkability maps are used, otherwise one suffices). A random walk model is used for efficient offline computation of the shrinkability maps. The latter are stored with the video to create a multi-sized video, which permits arbitrary-sized new versions of the video to be later very efficiently created in real-time, e.g. by a video-on-demand server supplying video streams to multiple devices with different resolutions. These shrinkability maps are highly compressible, so the resulting multi-sized videos are typically less than three times the size of the original compressed video. A scaling function operates on the multi-sized video, to give the new pixel locations in the result, giving a high-quality content-aware resized video.Despite the great efficiency and low storage requirements for our method, we produce results of comparable quality to state-of-the-art methods for content-aware image and video resizing.
Shape-simplifying Image Abstraction
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Kang, Henry; Lee, Seungyong
This paper presents a simple algorithm for producing stylistic abstraction of a photograph. Based on mean curvature flow in conjunction with shock filter, our method simplifies both shapes and colors simultaneously while preserving important features. In particular, we develop a constrained mean curvature flow, which outperforms the original mean curvature flow in conveying the directionality of features and shape boundaries. The proposed algorithm is iterative and incremental, and therefore the level of abstraction is intuitively controlled. Optionally, simple user masking can be incorporated into the algorithm to selectively control the abstraction speed and to protect particular regions. Experimental results show that our method effectively produces highly abstract yet feature-preserving illustrations from photographs.
Patch-type Segmentation of Voxel Shapes using Simplified Surface Skeletons
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Reniers, Dennie; Telea, Alexandru
We present a new method for decomposing a 3D voxel shape into disjoint segments using the shape s simplified surface-skeleton. The surface skeleton of a shape consists of 2D manifolds inside its volume. Each skeleton point has a maximally inscribed ball that touches the boundary in at least two contact points. A key observation is that the boundaries of the simplified fore- and background skeletons map one-to-one to increasingly fuzzy, soft convex, respectively concave, edges of the shape. Using this property, we build a method for segmentation of 3D shapes which has several desirable properties. Our method segments both noisy shapes and shapes with soft edges which vanish over low-curvature regions. Multiscale segmentations can be obtained by varying the simplification level of the skeleton. We present a voxel-based implementation of our approach and illustrate it on several realistic examples.
Reconstructing head models from photographs for individualized 3D-audio processing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Dellepiane, M.; Pietroni, N.; Tsingos, N.; Asselot, M.; Scopigno, R.
Visual fidelity and interactivity are the main goals in Computer Graphics research, but recently also audio is assuming an important role. Binaural rendering can provide extremely pleasing and realistic three-dimensional sound, but to achieve best results it s necessary either to measure or to estimate individual Head Related Transfer Function (HRTF). This function is strictly related to the peculiar features of ears and face of the listener. Recent sound scattering simulation techniques can calculate HRTF starting from an accurate 3D model of a human head. Hence, the use of binaural rendering on large scale (i.e. video games, entertainment) could depend on the possibility to produce a sufficiently accurate 3D model of a human head, starting from the smallest possible input. In this paper we present a completely automatic system, which produces a 3D model of a head starting from simple input data (five photos and some key-points indicated by user). The geometry is generated by extracting information from images and accordingly deforming a 3D dummy to reproduce user head features. The system proves to be fast, automatic, robust and reliable: geometric validation and preliminary assessments show that it can be accurate enough for HRTF calculation.
Context Aware Terrain Visualization for Wayfinding and Navigation
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Moeser, Sebastian; Degener, Patrick; Wahl, Roland; Klein, Reinhard
To assist wayfinding and navigation, the display of maps and driving directions on mobile devices is nowadays commonplace. While existing system can naturally exploit GPS information to facilitate orientation, the inherently limited screen space is often perceived as a drawback compared to traditional street maps as it constrains the perception of contextual information. Moreover, occlusion issues add to this problem if the environment is shown from the popular egocentric perspective.In this paper we describe an interactive visualization system that addresses these problems by reallocating the available screen space. At the heart of our system are three novel visualization techniques: First, we propose a non-standard perspective that allows to blend between the familiar pedestrian perspective and a standard map depiction with reduced occlusion. Second, we derive an efficient deformation technique that allows an interactive allocation of screen space to areas of interest like e.g. nearby touristic attractions. Finally, a path adaptive isometric perspective is proposed that reveals otherwise hidden facades in top-down views. We describe efficient implementations of all techniques and exemplify our interactive system on real world urban models.
View and Time Interpolation in Image Space
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Stich, Timo; Linz, Christian; Albuquerque, Georgia; Magnor, Marcus
The ability to interpolate between images taken at different time and viewpoints directly in image space opens up new possiblities. The goal of our work is to create plausible in-between images in real time without the need for an intermediate 3D reconstruction. This enables us to also interpolate between images recorded with uncalibrated and unsynchronized cameras. In our approach we use a novel discontiniuity preserving image deformation model to robustly estimate dense correspondences based on local homographies. Once correspondences have been computed we are able to render plausible in-between images in real time while properly handling occlusions. We discuss the relation of our approach to human motion perception and other image interpolation techniques.
Simulating Inextensible Cloth Using Impulses
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ye, Juntao
Computer simulation of cloth is often plagued by springs being over-stretched. The evaluation of impulses to prevent over-stretching is explained step-by-step. Our impulse approach controls the length of springs by a nonlinear system and then a novel linearization of it into a symmetric positive definite system. The cloth/solid collision handling is integrated into the linearized system seamlessly. Some results based on this method are also presented.
Part-type Segmentation of Articulated Voxel-Shapes using the Junction Rule
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Reniers, Dennie; Telea, Alexandru
We present a part-type segmentation method for articulated voxel-shapes based on curve skeletons. Shapes are considered to consist of several simpler, intersecting shapes. Our method is based on the junction rule: the observation that two intersecting shapes generate an additional junction in their joined curve-skeleton near the place of intersection. For each curve-skeleton point, we construct a piecewise-geodesic loop on the shape surface. Starting from the junctions, we search along the curve skeleton for points whose associated loops make for suitable part cuts. The segmentations are robust to noise and discretization artifacts, because the curve skeletonization incorporates a single user-parameter to filter spurious curve-skeleton branches. Furthermore, segment borders are smooth and minimally twisting by construction. We demonstrate our method on several real-world examples and compare it to existing part-type segmentation methods.
Knitting a 3D Model
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Igarashi, Yuki; Igarashi, Takeo; Suzuki, Hiromasa
A knitted animal is made of a closed surface consisting of several knitted patches knitted out of yarn and stuffed with cotton (Fig. 1). We introduce a system to create a knitting pattern from a given 3D surface model (mainly designed for rotund animal models). A knitting pattern is an instructional diagram describing how to knit yarn to obtain a desired shape. Since the creation of knitting patterns requires special skill, this is difficult for nonprofessionals. Our system automates the process and allows anyone to obtain his or her original knitting patterns from a 3D model. The system first covers the surface of the model with parallel winding strips of constant width. The system then samples the strip at constant intervals to convert it into a knitting pattern. The result is presented in a standard visual format so that the user can easily refer it during actual knitting. We show several examples of knitted animals created using the system.1Example of a knitted animal. A typical knitted animal consists of several circular and cylindrical patches.
Capturing Intention-based Full-Frame Video Stabilization
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Chen, Bing-Yu; Lee, Ken-Yi; Huang, Wei-Ting; Lin, Jong-Shan
Annoying shaky motion is one of the significant problems in home videos, since hand shake is an unavoidable effect when capturing by using a hand-held camcorder. Video stabilization is an important technique to solve this problem, but the stabilized videos resulting from some current methods usually have decreased resolution and are still not so stable. In this paper, we propose a robust and practical method of full-frame video stabilization while considering user s capturing intention to remove not only the high frequency shaky motions but also the low frequency unexpected movements. To guess the user s capturing intention, we first consider the regions of interest in the video to estimate which regions or objects the user wants to capture, and then use a polyline to estimate a new stable camcorder motion path while avoiding the user s interested regions or objects being cut out. Then, we fill the dynamic and static missing areas caused by frame alignment from other frames to keep the same resolution and quality as the original video. Furthermore, we smooth the discontinuous regions by using a three-dimensional Poisson-based method. After the above automatic operations, a full-frame stabilized video can be achieved and the important regions and objects can also be preserved.
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.

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