Full Papers 2008 - CGF 27-Issue 2

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https://diglib.eg.org/handle/10.2312/13880

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Accurate Shadows by Depth Complexity Sampling
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Forest, Vincent; Barthe, Loic; Paulin, Mathias
The accurate generation of soft shadows is a particularly computationally intensive task. In order to reduce rendering time, most real-time and offline applications decorrelate the generation of shadows from the computation of lighting. In addition to such approximations, they generate shadows using some restrictive assumptions only correct in very specific cases, leading to penumbra over-estimation or light-leaking artifacts. In this paper we present an algorithm that produces soft shadows without exhibiting the previous drawbacks. Using a new efficient evaluation of the number of occluders between two points (i.e. the depth complexity) we either modulate direct lighting or numerically solve the rendering equation for direct illumination. Our approach approximates shadows cast by semi-opaque occluders and naturally handles area lights with spatially varying luminance. Furthermore, depending on the desired performance and quality, the resulting shadows are either very close to, or as accurate as, a ray-traced reference. As a result, the presented method is well suited to many domains, ranging from quality-sensitive to performance-critical applications.
An Adaptive Contact Model for the Robust Simulation of Knots
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Spillmann, Jonas; Teschner, Matthias
In this paper, we present an adaptive model for dynamically deforming hyper-elastic rods. In contrast to existing approaches, adaptively introduced control points are not governed by geometric subdivision rules. Instead, their states are determined by employing a non-linear energy-minimization approach. Since valid control points are computed instantaneously, post-stabilization schemes are avoided and the stability of the dynamic simulation is improved.Due to inherently complex contact configurations, the simulation of knot tying using rods is a challenging task. In order to address this problem, we combine our adaptive model with a robust and accurate collision handling method for elastic rods. By employing our scheme, complex knot configurations can be simulated in a physically plausible way.
Agile Spectrum Imaging: Programmable Wavelength Modulation for Cameras and Projectors
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Mohan, Ankit; Raskar, Ramesh; Tumblin, Jack
We advocate the use of quickly-adjustable, computer-controlled color spectra in photography, lighting and displays. We present an optical relay system that allows mechanical or electronic color spectrum control and use it to modify a conventional camera and projector. We use a diffraction grating to disperse the rays into different colors, and introduce a mask (or LCD/DMD) in the optical path to modulate the spectrum. We analyze the trade-offs and limitations of this design, and demonstrate its use in a camera, projector and light source. We propose applications such as adaptive color primaries, metamer detection, scene contrast enhancement, photographing fluorescent objects, and high dynamic range photography using spectrum modulation.
Apparent Greyscale: A Simple and Fast Conversion to Perceptually Accurate Images and Video
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Smith, Kaleigh; Landes, Pierre-Edouard; Thollot, Joelle; Myszkowski, Karol
This paper presents a quick and simple method for converting complex images and video to perceptually accurate greyscale versions. We use a two-step approach first to globally assign grey values and determine colour ordering, then second, to locally enhance the greyscale to reproduce the original contrast. Our global mapping is image independent and incorporates the Helmholtz-Kohlrausch colour appearance effect for predicting differences between isoluminant colours. Our multiscale local contrast enhancement reintroduces lost discontinuities only in regions that insufficiently represent original chromatic contrast. All operations are restricted so that they preserve the overall image appearance, lightness range and differences, colour ordering, and spatial details, resulting in perceptually accurate achromatic reproductions of the colour original.
Articulated Object Reconstruction and Markerless Motion Capture from Depth Video
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Pekelny, Yuri; Gotsman, Craig
We present an algorithm for acquiring the 3D surface geometry and motion of a dynamic piecewise-rigid object using a single depth video camera. The algorithm identifies and tracks the rigid components in each frame, while accumulating the geometric information acquired over time, possibly from different viewpoints. The algorithm also reconstructs the dynamic skeleton of the object, thus can be used for markerless motion capture. The acquired model can then be animated to novel poses. We show the results of the algorithm applied to synthetic and real depth video.
Augmented Panoramic Video
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Hermans, C.; Vanaken, C.; Mertens, T.; Van Reeth, F.; Bekaert, P.
Many video sequences consist of a locally dynamic background containing moving foreground subjects. In this paper we propose a novel way of re-displaying these sequences, by giving the user control over a virtual camera frame. Based on video mosaicing, we first compute a static high quality background panorama. After segmenting and removing the foreground subjects from the original video, the remaining elements are merged into a dynamic background panorama, which seamlessly extends the original video footage. We then re-display this augmented video by warping and cropping the panorama. The virtual camera can have an enlarged field-of-view and a controlled camera motion. Our technique is able to process videos with complex camera motions, reconstructing high quality panoramas without parallax artefacts, visible seams or blurring, while retaining repetitive dynamic elements.
Automatic Conversion of Mesh Animations into Skeleton-based Animations
(The Eurographics Association and Blackwell Publishing Ltd, 2008) De Aguiar, Edilson; Theobalt, Christian; Thrun, Sebastian; Seidel, Hans-Peter
Recently, it has become increasingly popular to represent animations not by means of a classical skeleton-based model, but in the form of deforming mesh sequences. The reason for this new trend is that novel mesh deformation methods as well as new surface based scene capture techniques offer a great level of flexibility during animation creation. Unfortunately, the resulting scene representation is less compact than skeletal ones and there is not yet a rich toolbox available which enables easy post-processing and modification of mesh animations. To bridge this gap between the mesh-based and the skeletal paradigm, we propose a new method that automatically extracts a plausible kinematic skeleton, skeletal motion parameters, as well as surface skinning weights from arbitrary mesh animations. By this means, deforming mesh sequences can be fully-automatically transformed into fullyrigged virtual subjects. The original input can then be quickly rendered based on the new compact bone and skin representation, and it can be easily modified using the full repertoire of already existing animation tools.
The Beam Radiance Estimate for Volumetric Photon Mapping
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Jarosz, Wojciech; Zwicker, Matthias; Jensen, Henrik Wann
We present a new method for efficiently simulating the scattering of light within participating media. Using a theoretical reformulation of volumetric photon mapping, we develop a novel photon gathering technique for participating media. Traditional volumetric photon mapping samples the in-scattered radiance at numerous points along the length of a single ray by performing costly range queries within the photon map. Our technique replaces these multiple point-queries with a single beam-query, which explicitly gathers all photons along the length of an entire ray. These photons are used to estimate the accumulated in-scattered radiance arriving from a particular direction and need to be gathered only once per ray. Our method handles both fixed and adaptive kernels, is faster than regular volumetric photon mapping, and produces images with less noise.
Characterization for High Dynamic Range Imaging
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Kim, Min H.; Kautz, Jan
In this paper we present a new practical camera characterization technique to improve color accuracy in high dynamic range (HDR) imaging. Camera characterization refers to the process of mapping device-dependent signals, such as digital camera RAW images, into a well-defined color space. This is a well-understood process for low dynamic range (LDR) imaging and is part of most digital cameras - usually mapping from the raw camera signal to the sRGB or Adobe RGB color space. This paper presents an efficient and accurate characterization method for high dynamic range imaging that extends previous methods originally designed for LDR imaging. We demonstrate that our characterization method is very accurate even in unknown illumination conditions, effectively turning a digital camera into a measurement device that measures physically accurate radiance values - both in terms of luminance and color - rivaling more expensive measurement instruments.
CHC++: Coherent Hierarchical Culling Revisited
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Mattausch, Oliver; Bittner, Jiri; Wimmer, Michael
We present a new algorithm for efficient occlusion culling using hardware occlusion queries. The algorithm significantly improves on previous techniques by making better use of temporal and spatial coherence of visibility. This is achieved by using adaptive visibility prediction and query batching. As a result of the new optimizations the number of issued occlusion queries and the number of rendering state changes are significantly reduced. We also propose a simple method for determining tighter bounding volumes for occlusion queries and a method which further reduces the pipeline stalls. The proposed method provides up to an order of magnitude speedup over the previous state of the art. The new technique is simple to implement, does not rely on hardware calibration and integrates well with modern game engines.
Conformal Flattening by Curvature Prescription and Metric Scaling
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ben-Chen, Mirela; Gotsman, Craig; Bunin, Guy
We present an efficient method to conformally parameterize 3D mesh data sets to the plane. The idea behind our method is to concentrate all the 3D curvature at a small number of select mesh vertices, called cone singularities, and then cut the mesh through those singular vertices to obtain disk topology. The singular vertices are chosen automatically. As opposed to most previous methods, our flattening process involves only the solution of linear systems of Poisson equations, thus is very efficient. Our method is shown to be faster than existing methods, yet generates parameterizations having comparable quasi-conformal distortion.
Curvature-Domain Shape Processing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Eigensatz, Michael; Sumner, Robert W.; Pauly, Mark
We propose a framework for 3D geometry processing that provides direct access to surface curvature to facilitate advanced shape editing, filtering, and synthesis algorithms. The central idea is to map a given surface to the curvature domain by evaluating its principle curvatures, apply filtering and editing operations to the curvature distribution, and reconstruct the resulting surface using an optimization approach. Our system allows the user to prescribe arbitrary principle curvature values anywhere on the surface. The optimization solves a nonlinear least-squares problem to find the surface that best matches the desired target curvatures while preserving important properties of the original shape. We demonstrate the effectiveness of this processing metaphor with several applications, including anisotropic smoothing, feature enhancement, and multi-scale curvature editing.
Deep Opacity Maps
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Yuksel, Cem; Keyser, John
We present a new method for rapidly computing shadows from semi-transparent objects like hair. Our deep opacity maps method extends the concept of opacity shadow maps by using a depth map to obtain a per pixel distribution of opacity layers. This approach eliminates the layering artifacts of opacity shadow maps and requires far fewer layers to achieve high quality shadow computation. Furthermore, it is faster than the density clustering technique, and produces less noise with comparable shadow quality. We provide qualitative comparisons to these previous methods and give performance results. Our algorithm is easy to implement, faster, and more memory efficient, enabling us to generate high quality hair shadows in real-time using graphics hardware on a standard PC.
Detail-In-Context Visualization for Satellite Imagery
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Boettger, Joachim; Preiser, Martin; Balzer, Michael; Deussen, Oliver
We use the complex logarithm as a transformation for the visualization and navigation of highly complex satellite and aerial imagery. The resulting depictions show details and context with greatly different scales in one seamless image while avoiding local distortions. We motivate our approach by showing its relations to the ordinary perspective views and classical map projections. We discuss how to organize and process the huge amount of imagery in realtime using modern graphics hardware with an extended clipmapping technique. Finally, we provide details and experiences concerning the interpretation of and interaction with the resulting representations.
Distortion-Free Steganography for Polygonal Meshes
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Bogomjakov, Alexander; Gotsman, Craig; Isenburg, Martin
We present a technique for steganography in polygonal meshes. Our method hides a message in the indexed rep-resentation of a mesh by permuting the order in which faces and vertices are stored. The permutation is relative to a reference ordering that encoder and decoder derive from the mesh connectivity in a consistent manner. Our method is distortion-free because it does not modify the geometry of the mesh. Compared to previous steganographic methods for polygonal meshes our capacity is up to an order of magnitude better.Our steganography algorithm is universal and can be used instead of the standard permutation steganography algorithm on arbitrary datasets. The standard algorithm runs in (n2 log2 n log log n) time and achieves optimal O(nlog n) bit capacity on datasets with n elements. In contrast, our algorithm runs in O(n) time, achieves a capacity that is only one bit per element less than optimal, and is extremely simple to implement.
Dynamic Sampling and Rendering of Algebraic Point Set Surfaces
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Guennebaud, Gael; Germann, Marcel; Gross, Markus
Algebraic Point Set Surfaces (APSS) define a smooth surface from a set of points using local moving least-squares (MLS) fitting of algebraic spheres. In this paper we first revisit the spherical fitting problem and provide a new, more generic solution that includes intuitive parameters for curvature control of the fitted spheres. As a second contribution we present a novel real-time rendering system of such surfaces using a dynamic up-sampling strategy combined with a conventional splatting algorithm for high quality rendering. Our approach also includes a new view dependent geometric error tailored to efficient and adaptive up-sampling of the surface. One of the key features of our system is its high degree of flexibility that enables us to achieve high performance even for highly dynamic data or complex models by exploiting temporal coherence at the primitive level. We also address the issue of efficient spatial search data structures with respect to construction, access and GPU friendliness. Finally, we present an efficient parallel GPU implementation of the algorithms and search structures.
Effect of Character Animacy and Preparatory Motion on Perceptual Magnitude of Errors in Ballistic Motion
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Reitsma, P. S. A.; Andrews, J.; Pollard, N. S.
An increasing number of projects have examined the perceptual magnitude of visible artifacts in animated motion. These studies have been performed using a mix of character types, from detailed human models to abstract geometric objects such as spheres. We explore the extent to which character morphology influences user sensitivity to errors in a fixed set of ballistic motions replicated on three different character types. We find user sensitivity responds to changes in error type or magnitude in a similar manner regardless of character type, but that users display a higher sensitivity to some types of errors when these errors are displayed on more human-like characters. Further investigation of those error types suggests that being able to observe a period of preparatory motion before the onset of ballistic motion may be important. However, we found no evidence to suggest that a mismatch between the preparatory phase and the resulting ballistic motion was responsible for the higher sensitivity to errors that was observed for the most humanlike character.
Efficient and Dynamic Simplification of Line Drawings
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Shesh, Amit; Chen, Baoquan
In this paper we present a pipeline for rendering dynamic 2D/3D line drawings efficiently. Our main goal is to create efficient static renditions and coherent animations of line drawings in a setting where lines can be added, deleted and arbitrarily transformed on-the-fly. Such a dynamic setting enables us to handle interactively sketched 2D line data, as well as arbitrarily transformed 3D line data in a unified manner. We evaluate the proximity of screen projected strokes to simplify them while preserving their continuity. We achieve this by using a special data structure that facilitates efficient proximity calculations in a dynamic setting. This on-the-fly proximity evaluation also facilitates generation of appropriate visibility cues to mitigate depth ambiguities and visual clutter for 3D line data. As we perform all these operations using only line data, we can create line drawings from 3D models without any surface information. We demonstrate the effectiveness and applicability of our approach by showing several examples with initial line representations obtained from a variety of sources: 2D and 3D hand-drawn sketches and 3D salient geometry lines obtained from 3D surface representations.
An Example-based Procedural System for Element Arrangement
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ijiri, Takashi; Mech, Radomir; Igarashi, Takeo; Miller, Gavin
We present a method for synthesizing two dimensional (2D) element arrangements from an example. The main idea is to combine texture synthesis techniques based-on a local neighborhood comparison and procedural modeling systems based-on local growth. Given a user-specified reference pattern, our system analyzes neigh-borhood information of each element by constructing connectivity. Our synthesis process starts with a single seed and progressively places elements one by one by searching a reference element which has local features that are the most similar to the target place of the synthesized pattern. To support creative design activities, we introduce three types of interaction for controlling global features of the resulting pattern, namely a spray tool, a flow field tool, and a boundary tool. We also introduce a global optimization process that helps to avoid local error concentrations. We illustrate the feasibility of our method by creating several types of 2D patterns.
Expressive Facial Gestures From Motion Capture Data
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Ju, Eunjung; Lee, Jehee
Human facial gestures often exhibit such natural stochastic variations as how often the eyes blink, how often the eyebrows and the nose twitch, and how the head moves while speaking. The stochastic movements of facial features are key ingredients for generating convincing facial expressions. Although such small variations have been simulated using noise functions in many graphics applications, modulating noise functions to match natural variations induced from the affective states and the personality of characters is difficult and not intuitive. We present a technique for generating subtle expressive facial gestures (facial expressions and head motion) semi-automatically from motion capture data. Our approach is based on Markov random fields that are simulated in two levels. In the lower level, the coordinated movements of facial features are captured, parameterized, and transferred to synthetic faces using basis shapes. The upper level represents independent stochastic behavior of facial features. The experimental results show that our system generates expressive facial gestures synchronized with input speech.

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