25-Issue 3

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https://diglib.eg.org/handle/10.2312/126

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An Improved Physically-Based Soft Shadow Volume Algorithm
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Lehtinen, Jaakko; Laine, Samuli; Aila, Timo
We identify and analyze several performance problems in a state-of-the-art physically-based soft shadow volume algorithm, and present an improved method that alleviates these problems by replacing an overly conservative spatial acceleration structure by a more efficient one. The new technique consistently outperforms both the previous method and a ray tracing-based reference solution in several realistic situations while retaining the correctness of the solution and other desirable characteristics of the previous method. These include the unintrusiveness of the original algorithm, meaning that our method can be used as a black-box shadow solver in any offline renderer without requiring multiple passes over the image or other special accommodation. We achieve speedup factors from 1.6 to 12.3 when compared to the previous method.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Three-Dimensional Graphics and Realism]: Shadowing
Preface
(The Eurographics Association and Blackwell Publishing, Inc, 2006)
Beyond Tone Mapping: Enhanced Depiction of Tone Mapped HDR Images
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Smith, Kaleigh; Krawczyk, Grzegorz; Myszkowski, Karol; Seidel, Hans-Peter
High Dynamic Range (HDR) images capture the full range of luminance present in real world scenes, and unlike Low Dynamic Range (LDR) images, can simultaneously contain detailed information in the deepest of shadows and the brightest of light sources. For display or aesthetic purposes, it is often necessary to perform tone mapping, which creates LDR depictions of HDR images at the cost of contrast information loss. The purpose of this work is two-fold: to analyze a displayed LDR image against its original HDR counterpart in terms of perceived contrast distortion, and to enhance the LDR depiction with perceptually driven colour adjustments to restore the original HDR contrast information. For analysis, we present a novel algorithm for the characterization of tone mapping distortion in terms of observed loss of global contrast, and loss of contour and texture details. We classify existing tone mapping operators accordingly. We measure both distortions with perceptual metrics that enable the automatic and meaningful enhancement of LDR depictions. For image enhancement, we identify artistic and photographic colour techniques from which we derive adjustments that create contrast with colour. The enhanced LDR image is an improved depiction of the original HDR image with restored contrast information.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.4.0 [Image Processing and Computer Vision]: GeneralImage processing software
Topological Structures in Two-Parameter-Dependent 2D Vector Fields
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Weinkauf, T.; Theisel, H.; Hege, H.-C.; Seidel, H.-P.
In this paper we extract and visualize the topological skeleton of two-parameter-dependent vector fields. This kind of vector data depends on two parameter dimensions, for instance physical time and a scale parameter. We show that two important classes of local bifurcations - fold and Hopf bifurcations - build line structures for which we present an approach to extract them. Furthermore we show that new kinds of structurally stable local bifurcations exist for this data, namely fold-fold and Hopf-fold bifurcations. We present a complete classification of them. We apply our topological extraction method to analyze a number of two-parameter-dependent vector fields with different physical interpretations of the two additional dimensions.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Line and Curve Generation I.3.3 [Computer Graphics]: Picture/Image Generation
Towards a Unified Dynamical Solver for Computer Graphics
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Stam, Jos
In this talk I will present some research I have done over the past few years in developing a unified dynamical solver for computer graphics. Currently many solvers are specialized for a given phenomenon such as fluid flow, cloth, rigid bodies, hair, etc. Having these different solvers interact is sometimes problematic. We propose to model all matter as a linked particle system having the topology of a simplicial complex. The dynamical complex evolves due to external forces like gravity and constraints such as collisions and internal deformation energies. We use a solution scheme that iteratively updates the velocities to achieve all constraints. Key to the stability of our system is to interleave the solve for the different constraints. The talk will cover the main ideas and ingredients of our solver and will be accompanied with live demonstrations.
Splicing Upper-Body Actions with Locomotion
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Heck, Rachel; Kovar, Lucas; Gleicher, Michael
This paper presents a simple and efficient technique for synthesizing high-fidelity motions by attaching, or splicing, the upper-body action of one motion example to the lower-body locomotion of another. Existing splicing algorithms do little more than copy degrees of freedom (DOFs) from one motion onto another. This naive DOF replacement can produce unrealistic results because it ignores both physical and stylistic correlations between various joints in the body. Our approach uses spatial and temporal relationships found within the example motions to retain the overall posture of the upper-body action while adding secondary motion details appropriate to the timing and configuration of the lower body. By decoupling upper-body action from lower-body locomotion, our motion synthesis technique allows example motions to be captured independently and later combined to create new natural looking motions.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation
A Robust Two-Step Procedure for Quad-Dominant Remeshing
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Marinov, Martin; Kobbelt, Leif
We propose a new technique for quad-dominant remeshing which separates the local regularity requirements from the global alignment requirements by working in two steps. In the first step, we apply a slight variant of variational shape approximation in order to segment the input mesh into patches which capture the global structure of the processed object. Then we compute an optimized quad-mesh for every patch by generating a finite set of candidate curves and applying a combinatorial optimization procedure. Since the optimization is performed independently for each patch, we can afford more complex operations while keeping the overall computation times at a reasonable level. Our quad-meshing technique is robust even for noisy meshes and meshes with isotropic or flat regions since it does not rely on the generation of curves by integration along estimated principal curvature directions. Instead we compute a conformal parametrization for each patch and generate the quad-mesh from curves with minimum bending energy in the 2D parameter domain. Mesh consistency between patches is guaranteed by simply using the same set of sample points along the common boundary curve. The resulting quad-meshes are of high-quality locally (shape of the quads) as well as globally (global alignment) which allows us to even generate fairly coarse quad-meshes that can be used as Catmull-Clark control meshes.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Geometric algorithms, languages, and systems
C-BDAM - Compressed Batched Dynamic Adaptive Meshes for Terrain Rendering
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Gobbetti, E.; Marton, F.; Cignoni, P.; Di Benedetto, M.; Ganovelli, F.
We describe a compressed multiresolution representation for supporting interactive rendering of very large planar and spherical terrain surfaces. The technique, called Compressed Batched Dynamic Adaptive Meshes (C-BDAM), is an extension of the BDAM and P-BDAM chunked level-of-detail hierarchy. In the C-BDAM approach, all patches share the same regular triangulation connectivity and incrementally encode their vertex attributes using a quantized representation of the difference with respect to values predicted from the coarser level. The structure provides a number of benefits: simplicity of data structures, overall geometric continuity for planar and spherical domains, support for variable resolution input data, management of multiple vertex attributes, efficient compression and fast construction times, ability to support maximum-error metrics, real-time decompression and shaded rendering with configurable variable level-of-detail extraction, and runtime detail synthesis. The efficiency of the approach and the achieved compression rates are demonstrated on a number of test cases, including the interactive visualization of a 29 gigasample reconstruction of the whole planet Earth created from high resolution SRTM data.Categories and Subject Descriptors (according toACMCCS): I.3.3 [Computer Graphics]: Picture and Image Generation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.
Semantic Photo Synthesis
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Johnson, M.; Brostow, G. J.; Shotton, J.; Arandjelovic, O.; Kwatra, V.; Cipolla, R.
Composite images are synthesized from existing photographs by artists who make concept art, e.g., storyboards for movies or architectural planning. Current techniques allow an artist to fabricate such an image by digitally splicing parts of stock photographs. While these images serve mainly to quickly convey how a scene should look, their production is laborious. We propose a technique that allows a person to design a new photograph with substantially less effort. This paper presents a method that generates a composite image when a user types in nouns, such as boat and sand. The artist can optionally design an intended image by specifying other constraints. Our algorithm formulates the constraints as queries to search an automatically annotated image database. The desired photograph, not a collage, is then synthesized using graph-cut optimization, optionally allowing for further user interaction to edit or choose among alternative generated photos. An implementation of our approach, shown in the associated video, demonstrates our contributions of (1) a method for creating specific images with minimal human effort, and (2) a combined algorithm for automatically building an image library with semantic annotations from any photo collection.
Reflected-Scene Impostors for Realistic Reflections at Interactive Rates
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Popescu, Voicu; Mei, Chunhui; Dauble, Jordan; Sacks, Elisha
We present a technique for rendering reflections on complex reflectors at interactive rates based on approximating the geometry of the reflected scene with impostors. The reflections correctly convey the distance to the reflector surface and provide motion parallax. Two types of impostors are adapted to the reflections framework: billboards and depth maps. Billboards remove most of the problems of environment mapped reflections at only a small additional cost. Second order reflections are supported by introducing reflective billboards. Higher quality reflections that provide motion parallax within a reflected object are obtained by approximating the reflective geometry with depth maps. The computation of the intersection between a reflected ray and a depth map is accelerated by leveraging epipolar constraints. Like environment mapping, our technique does not pose any restriction on the geometry of the reflector, supports dynamic scenes, and runs at interactive rates with the help of graphics hardware.Categories and Subject Descriptors (ACM CCS): I.3.3. [Computer Graphics]-Three-Dimensional Graphics and Realism.
Dancing-to-Music Character Animation
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Shiratori, Takaaki; Nakazawa, Atsushi; Ikeuchi, Katsushi
In computer graphics, considerable research has been conducted on realistic human motion synthesis. However, most research does not consider human emotional aspects, which often strongly affect human motion. This paper presents a new approach for synthesizing dance performance matched to input music, based on the emotional aspects of dance performance. Our method consists of a motion analysis, a music analysis, and a motion synthesis based on the extracted features. In the analysis steps, motion and music feature vectors are acquired. Motion vectors are derived from motion rhythm and intensity, while music vectors are derived from musical rhythm, structure, and intensity. For synthesizing dance performance, we first find candidate motion segments whose rhythm features are matched to those of each music segment, and then we find the motion segment set whose intensity is similar to that of music segments. Additionally, our system supports having animators control the synthesis process by assigning desired motion segments to the specified music segments. The experimental results indicate that our method actually creates dance performance as if a character was listening and expressively dancing to the music.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism Animation; J.5 [Arts and Humanities]: Performing Arts Music
Silhouette Extraction in Hough Space
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Olson, Matt; Zhang , Hao
Object-space silhouette extraction is an important problem in fields ranging from non-photorealistic computer graphics to medical robotics. We present an efficient silhouette extractor for triangle meshes under perspective projection and make three contributions. First, we describe a novel application of 3D Hough transforms, which allows us to organize mesh data more effectively for silhouette computations than the traditional dual transform. Next, we introduce an incremental silhouette update algorithm which operates on an octree augmented with neighbour information and optimized for efficient low-level traversal. Finally, we present a method for initial extraction of silhouette, using the same data structure, whose performance is linear in the size of the extracted silhouette. We demonstrate significant performance improvements given by our approach over the current state of the art.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Three-Dimensional Graphics and Realism]: Visible line/surface algorithms
Multiresolution Random Accessible Mesh Compression
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Kim, Junho; Choe, Sungyul; Lee, Seungyong
This paper presents a novel approach for mesh compression, which we call multiresolution random accessible mesh compression. In contrast to previous mesh compression techniques, the approach enables us to progressively decompress an arbitrary portion of a mesh without decoding other non-interesting parts. This simultaneous support of random accessibility and progressiveness is accomplished by adapting selective refinement of a multiresolution mesh to the mesh compression domain. We present a theoretical analysis of our connectivity coding scheme and provide several experimental results. The performance of our coder is about 11 bits for connectivity and 21 bits for geometry with 12-bit quantization, which can be considered reasonably good under the constraint that no fixed neighborhood information can be used for coding to support decompression in a random order.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling
Projective Alpha Colour
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Willis, Philip
Alpha colours were introduced for image compositing, using a pixel coverage model. Algebraically they resemble homogeneous coordinates, widely used in projective geometry calculations. We show why this is the case. This allows us to extend alpha beyond compositing, to all colour calculations regardless of whether pixels are involved and without the need for a coverage model. Our approach includes multi-channel spectral calculations and removes the need for 7 channel and 6 channel alpha colour operations. It provides a unified explanation of pre-multiplied and non pre-multiplied colours, including negative coordinates and infinite points in colour space. It permits filter and illumination operations. It unifies the three existing significant compositing models in a single framework. It achieves this with a physically-plausible energy basis.Keywords: projective geometry, homogeneous coordinates, image compositing, alpha blending, alpha compositing, colour representation, filtering, spectral colour, projective alpha colour
Creating Face Models from Vague Mental Images
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Blanz, V.; Albrecht, I.; Haber, J.; Seidel, H.-P.
We present a novel approach to create plausible 3D face models from vague recollections or incomplete descriptions. This task plays an important role in police work, where composite facial images of suspects need to be created from vague descriptions given by the eyewitnesses of an incident.Our approach is based on a morphable model of 3D faces and takes into account correlations among facial features based on human anatomy and ethnicity. Using these correlations, unspecified parts of the target face are automatically completed to yield a coherent face model. The system uses a novel paradigm for navigating face space and provides high-level control of facial attributes as well as the possibility to import facial features from a database. In addition, the user can specify a set of attribute constraints that are used to restrict the target face to a residual subspace. These constraints can also be enforced on the example faces in the database, bringing their appearance closer to the mental image of the user, and thus avoiding confusing exposure to entirely different faces. We also propose a novel approach for adapting the system to local populations based on additional image databases that are converted into our 3D representation by automated shape reconstruction.We demonstrate the applicability of our system in a simulated forensic scenario and compare our results with those obtained by a professional forensic artist using state-of-the-art software for creating composite images in police work.Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Computer Graphics]: Methodology and Techniques-Interaction techniques I.4.10 [Image Processing and Computer Vision]: Image Representation-Hierarchical, Multidimensional, Statistical J.m [Computer Applications]: Miscellaneous-Forensic Sciences
Opacity Peeling for Direct Volume Rendering
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Rezk-Salama, Christof; Kolb, Andreas
The most important technique to visualize 3D scalar data, as they arise e.g. in medicine from tomographic measurement, is direct volume rendering. A transfer function maps the scalar values to optical properties which are used to solve the integral of light transport in participating media. Many medical data sets, especially MRI data, however, are difficult to visualize due to different tissue types being represented by the same scalar value. The main problem is that interesting structures will be occluded by less important structures because they share the same range of data values. Occlusion, however, is a view-dependent problem and cannot be solved easily by transfer function design. This paper proposes a new method to display different entities inside the volume data in a single rendering pass. The proposed opacity peeling technique reveals structures in the data set that cannot be visualized directly by one-or multi-dimensional transfer functions without explicit segmentation. We also demonstrate real-time implementations using texture mapping and multiple render targets.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Sweep-based Freeform Deformations
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Yoon, Seung-Hyun; Kim, Myung-Soo
We propose a sweep-based approach to the freeform deformation of three-dimensional objects. Instead of using a volume enclosing the whole object, we approximate only its deformable parts using sweep surfaces. The vertices on the object boundary are bound to the sweep surfaces and follow their deformation. Several sweep surfaces can be organized into a hierarchy so that they interact with each other in a controlled manner. Thus we can support intuitively plausible shape deformation of objects of arbitrary topology with multiple control handles. A sweep-based approach also provides important advantages such as volume preservation. We demonstrate the effectiveness of our technique in several examples.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computational Geometry and Object Modeling]: Curve, surface, solid, and object representations
A Primer on Topological Persistence
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Edelsbrunner, Herbert
The idea of topological persistence is to look at homological features that persist along a nested sequence of topo-logical spaces. As a typical example, we may take the sequence of sublevel sets of a function. The combinatorial characterization of persistence in terms of pairs of critical values and fast algorithms computing these pairs make this idea practical and useful in dealing with the pervasive phenomenon of noise in geometric and visual data. This talk will1. recall the relatively short history of persistence and some of its older roots;2. introduce the concept intuitively while pointing out where algebra is needed to solidify the more difficult steps;3. discuss a few applications to give a feeling of the potential of the method in dealing with noise and scale.Besides the initial concept, the talk will touch upon recent extensions and their motivation.
Accurate Specular Reflections in Real-Time
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Roger, David; Holzschuch, Nicolas
Specular reflections provide many important visual cues in our daily environment. They inform us of the shape of objects, of the material they are made of, of their relative positions, etc. Specular reflections on curved objects are usually approximated using environment maps. In this paper, we present a new algorithm for real-time computation of specular reflections on curved objects, based on an exact computation for the reflection of each scene vertex. Our method exhibits all the required parallax effects and can handle arbitrary proximity between the reflector and the reflected objects.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Wrinkling Coarse Meshes on the GPU
(The Eurographics Association and Blackwell Publishing, Inc, 2006) Loviscach, J.
The simulation of complex layers of folds of cloth can be handled through algorithms which take the physical dynamics into account. In many cases, however, it is sufficient to generate wrinkles on a piece of garment which mostly appears spread out. This paper presents a corresponding fully GPU-based, easy-to-control, and robust method to generate and render plausible and detailed folds. This simulation is generated from an animated mesh. A relaxation step ensures that the behavior remains globally consistent. The resulting wrinkle field controls the lighting and distorts the texture in a way which closely simulates an actually deformed surface. No highly tessellated mesh is required to compute the position of the folds or to render them. Furthermore, the solution provides a 3D paint interface through which the user may bias the computation in such a way that folds already appear in the rest pose.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation, I.3.7 [Computer Graphics]: Color, shading, shadowing, and texture

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