27-Issue 2

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https://diglib.eg.org/handle/10.2312/135

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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.
Ray Casting Algebraic Surfaces using the Frustum Form
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Reimers, Martin; Seland, Johan
We propose an algorithm for interactive ray-casting of algebraic surfaces of high degree. A key point of our approach is a polynomial form adapted to the view frustum. This so called frustum form yields simple expressions for the Bernstein form of the ray equations, which can be computed efficiently using matrix products and pre-computed quantities. Numerical root-finding is performed using B-spline and Bezier techniques, and we compare the performances of recent and classical algorithms. Furthermore, we propose a simple and fairly efficient anti-aliasing scheme, based on a combination of screen space and object space techniques. We show how our algorithms can be implemented on streaming architectures with single precision, and demonstrate interactive frame-rates for degrees up to 16.
Simulation of Human Motion Data using Short-Horizon Model-Predictive Control
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Da Silva, M.; Abe, Y.; Popovic, J.
Many data-driven animation techniques are capable of producing high quality motions of human characters. Few techniques, however, are capable of generating motions that are consistent with physically simulated environments. Physically simulated characters, in contrast, are automatically consistent with the environment, but their motions are often unnatural because they are difficult to control. We present a model-predictive controller that yields natural motions by guiding simulated humans toward real motion data. During simulation, the predictive component of the controller solves a quadratic program to compute the forces for a short window of time into the future. These forces are then applied by a low-gain proportional-derivative component, which makes minor adjustments until the next planning cycle. The controller is fast enough for interactive systems such as games and training simulations. It requires no precomputation and little manual tuning. The controller is resilient to mismatches between the character dynamics and the input motion, which allows it to track motion capture data even where the real dynamics are not known precisely. The same principled formulation can generate natural walks, runs, and jumps in a number of different physically simulated surroundings.
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.
Visualizing Underwater Ocean Optics
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Gutierrez, Diego; Seron, Francisco J.; Munoz, Adolfo; Anson, Oscar
Simulating the in-water ocean light field is a daunting task. Ocean waters are one of the richest participating media, where light interacts not only with water molecules, but with suspended particles and organic matter as well. The concentration of each constituent greatly affects these interactions, resulting in very different hues. Inelastic scattering events such as fluorescence or Raman scattering imply energy transfers that are usually neglected in the simulations. Our contributions in this paper are a bio-optical model of ocean waters suitable for computer graphics simulations, along with an improved method to obtain an accurate solution of the in-water light field based on radiative transfer theory. The method provides a link between the inherent optical properties that define the medium and its apparent optical properties, which describe how it looks. The bio-optical model of the ocean uses published data from oceanography studies. For inelastic scattering we compute all frequency changes at higher and lower energy values, based on the spectral quantum efficiency function of the medium. The results shown prove the usability of the system as a predictive rendering algorithm. Areas of application for this research span from underwater imagery to remote sensing; the resolution method is general enough to be usable in any type of participating medium simulation.
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.
Spectral Geometry Processing with Manifold Harmonics
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Vallet, B.; Levy, B.
We present an explicit method to compute a generalization of the Fourier Transform on a mesh. It is well known that the eigenfunctions of the Laplace Beltrami operator (Manifold Harmonics) define a function basis allowing for such a transform. However, computing even just a few eigenvectors is out of reach for meshes with more than a few thousand vertices, and storing these eigenvectors is prohibitive for large meshes. To overcome these limitations, we propose a band-by-band spectrum computation algorithm and an out-of-core implementation that can compute thousands of eigenvectors for meshes with up to a million vertices. We also propose a limited-memory filtering algorithm, that does not need to store the eigenvectors. Using this latter algorithm, specific frequency bands can be filtered, without needing to compute the entire spectrum. Finally, we demonstrate some applications of our method to interactive convolution geometry filtering. These technical achievements are supported by a solid yet simple theoretic framework based on Discrete Exterior Calculus (DEC). In particular, the issues of symmetry and discretization of the operator are considered with great care.
Image-based Aging Using Evolutionary Computing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Hubball, Daniel; Chen, Min; Grant, Phil W.
Aging has considerable visual effects on the human face and is difficult to simulate using a universally-applicable global model. In this paper, we focus on the hypothesis that the patterns of age progression (and regression) are related to the face concerned, as the latter implicitly captures the characteristics of gender, ethnic origin, and age group, as well as possibly the person-specific development patterns of the individual. We use a data-driven framework for automatic image-based facial transformation in conjunction with a database of facial images. We build a novel parameterized model for encoding age-transformation in addition with the traditional model for face description. We utilize evolutionary computing to learn the relationship between the two models. To support this work, we also developed a new image warping algorithm based on non-uniform radial basis functions (NURBFs). Evolutionary computing was also used to handle the large parameter space associated with NURBFs. In comparison with several different methods, it consistently provides the best results against the ground truth.
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.
Video Relighting Using Infrared Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Wang, Oliver; Davis, James; Chuang, Erika; Rickard, Ian; De Mesa, Krystle; Dave, Chirag
Inappropriate lighting is often responsible for poor quality video. In most offices and homes, lighting is not designed for video conferencing. This can result in unevenly lit faces, distracting shadows, and unnatural colors. We present a method for relighting faces that reduces the effects of uneven lighting and color. Our setup consists of a compact lighting rig and a camera that is both inexpensive and inconspicuous to the user. We use unperceivable infrared (IR) lights to obtain an illumination bases of the scene. Our algorithm computes an optimally weighted combination of IR bases to minimize lighting inconsistencies in foreground areas and reduce the effects of colored monitor light. However, IR relighting alone results in images with an unnatural ghostly appearance, thus a retargeting technique is presented which removes the unnatural IR effects and produces videos that have substantially more balanced intensity and color than the original video.
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.
Floating Textures
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Eisemann, M.; De Decker, B.; Magnor, M.; Bekaert, P.; De Aguiar, E.; Ahmed, N.; Theobalt, C.; Sellent, A.
We present a novel multi-view, projective texture mapping technique. While previous multi-view texturing approaches lead to blurring and ghosting artefacts if 3D geometry and/or camera calibration are imprecise, we propose a texturing algorithm that warps ( floats ) projected textures during run-time to preserve crisp, detailed texture appearance. Our GPU implementation achieves interactive to real-time frame rates. The method is very generally applicable and can be used in combination with many image-based rendering methods or projective texturing applications. By using Floating Textures in conjunction with, e.g., visual hull rendering, light field rendering, or free-viewpoint video, improved rendering results are obtained from fewer input images, less accurately calibrated cameras, and coarser 3D geometry proxies.
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.
Manifold-valued Thin-Plate Splines with Applications in Computer Graphics
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Steinke, Florian; Hein, Matthias; Peters, Jan; Schoelkopf, Bernhard
We present a generalization of thin-plate splines for interpolation and approximation of manifold-valued data, and demonstrate its usefulness in computer graphics with several applications from different fields. The cornerstone of our theoretical framework is an energy functional for mappings between two Riemannian manifolds which is independent of parametrization and respects the geometry of both manifolds. If the manifolds are Euclidean, the energy functional reduces to the classical thin-plate spline energy. We show how the resulting optimization problems can be solved efficiently in many cases. Our example applications range from orientation interpolation and motion planning in animation over geometric modelling tasks to color interpolation.
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.
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.
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.
Image-based Shaving
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Nguyen, Minh Hoai; Lalonde, Jean-Francois; Efros, Alexei A.; De la Torre, Fernando
Many categories of objects, such as human faces, can be naturally viewed as a composition of several different layers. For example, a bearded face with glasses can be decomposed into three layers: a layer for glasses, a layer for the beard and a layer for other permanent facial features. While modeling such a face with a linear subspace model could be very difficult, layer separation allows for easy modeling and modification of some certain structures while leaving others unchanged. In this paper, we present a method for automatic layer extraction and its applications to face synthesis and editing. Layers are automatically extracted by utilizing the differences between subspaces and modeled separately. We show that our method can be used for tasks such beard removal (virtual shaving), beard synthesis, and beard transfer, among others.
Frontmatter
(The Eurographics Association and Blackwell Publishing Ltd, 2008)
Stereo Light Probe
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Corsini, Massimiliano; Callieri, Marco; Cignoni, Paolo
In this paper we present a practical, simple and robust method to acquire the spatially-varying illumination of a real-world scene. The basic idea of the proposed method is to acquire the radiance distribution of the scene using high-dynamic range images of two reflective balls. The use of two light probes instead of a single one allows to estimate, not only the direction and intensity of the light sources, but also the actual position in space of the light sources. To robustly achieve this goal we first rectify the two input spherical images, then, using a region-based stereo matching algorithm, we establish correspondences and compute the position of each light. The radiance distribution so obtained can be used for augmented reality applications, photo-realistic rendering and accurate reflectance properties estimation. The accuracy and the effectiveness of the method have been tested by measuring the computed light position and rendering synthetic version of a real object in the same scene. The comparison with standard method that uses a simple spherical lighting environment is also shown.

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