EG2008

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https://diglib.eg.org/handle/10.2312/264

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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.
Perceptually-Motivated Graphics
(The Eurographics Association, 2008) Mania, Katerina; Reinhard, Erik; Maria Roussou and Jason Leigh
In this half-day tutorial, we give an overview of the uses of knowledge about the human visual system, as applied to several aspects of computer graphics. In particular, we show how human visual perception applies to the optimization of rendering algorithms, display algorithms, as well as virtual environments. Examples are shown for applications such as real-time rendering, high quality rendering, material editing using images, and training and knowledge transfer in virtual environments. The aim is to show that the human visual perception literature harbours a rich source of knowledge that can be directly applied to improve a wide range of algorithms and technologies in computer graphics.
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.
Efficient Visualization of Architectural Models from a Structure and Motion Pipeline
(The Eurographics Association, 2008) Farenzena, Michela; Fusiello, Andrea; Gherardi, Riccardo; Katerina Mania and Eric Reinhard
State of the art three dimensional reconstruction pipelines can nowadays produce models up to several million polygons without any human intervention from a set of digital images or video. Such models are able to stretch the rendering capabilities of current hardware. We propose to augment a typical structure from motion pipeline with two additional steps, automatic fitting of high-level solid primitives and relief maps extraction, thus recovering both the overall structure of a building and its fine geometry. This not only gives birth to a more tractable and semantic model of the imaged scene, but allows for efficient and compelling rendering. We substantiate our claims showing a complete example of the described system.
A Taxonomy of Modeling Techniques using Sketch-Based Interfaces
(The Eurographics Association, 2008) Olsen, L.; Samavati, F. F.; Sousa, M. Costa; Jorge, J.; Theoharis Theoharis and Philip Dutre
Traditional user interfaces in modeling have followed the WIMP (Window, Icon, Menu, Pointer) paradigm. While functional and powerful, they can also be cumbersome and daunting to a novice user; creating a complex model requires much expertise and effort. A recent trend is toward more accessible and natural interfaces, which has lead to sketch-based interfaces for modeling (SBIM). The goal is to allow hand-drawn sketches to be used in the modeling process, from rough model creation through to fine detail construction. Mapping 2D sketches to a 3D modeling operation is a difficult and ambiguous task, so our categorization is based on how an SBIM application chooses to interpret a sketch, of which there are three primary methods: to create a 3D model, to add details to an existing model, or to deform and manipulate a model. In this STAR, we present a taxonomy of sketchbased interfaces focused on geometric modeling applications. The canonical and recent works are presented and classified, including techniques for sketch acquisition, filtering, and interpretation. The report also includes a discussion of important challenges and open problems for researchers to tackle in the coming years.
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.
Laziness is a Virtue: Motion Stitching Using Effort Minimization
(The Eurographics Association, 2008) Li, Lei; McCann, James; Faloutsos, Christos; Pollard, Nancy; Katerina Mania and Eric Reinhard
Given two motion-capture sequences that are to be stitched together, how can we assess the goodness of the stitching? The straightforward solution, Euclidean distance, permits counter-intuitive results because it ignores the effort required to actually make the stitch. The main contribution of our work is that we propose an intuitive, first-principles approach, by computing the effort that is needed to do the transition (laziness-effort, or L-score ). Our conjecture is that, the smaller the effort, the more natural the transition will seem to humans. Moreover, we propose the elastic L-score which allows for elongated stitching, to make a transition as natural as possible. We present preliminary experiments on both artificial and real motions which show that our L-score approach indeed agrees with human intuition, it chooses good stitching points, and generates natural transition paths.
Interactive Stroke-Based NPR using Hand Postures on Large Displays
(The Eurographics Association, 2008) Grubert, Jens; Carpendale, Sheelagh; Isenberg, Tobias; Katerina Mania and Eric Reinhard
We explore the use of hand postures to interact with stroke-based rendering (SBR) on touch-sensitive large displays. In contrast to traditional WIMP interfaces, we allow people to directly engage with and influence a rendering. Our system allows the creation of new stroke primitives as well as provides mechanisms to distribute and then manipulate them on the canvas. We offer a set of natural mappings from hand postures to rendering parameterizations. The resulting system allows an intuitive exploration of SBR without the need for traditional desktop interfaces.
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.
Artificial Mosaics by Gradient Vector Flow
(The Eurographics Association, 2008) Battiato, Sebastiano; Blasi, Gianpiero Di; Gallo, Giovanni; Guarnera, Giuseppe Claudio; Puglisi, Giovanni; Katerina Mania and Eric Reinhard
In this paper a novel approach for artificial mosaic generation is proposed. Gradient Vector Flow computation together with heuristics to maximise the covered mosaic area are used. The high frequency details are managed in a global way allowing to preserve the mosaic-style also for small ones. Experiments and comparisons with previous works confirm the effectiveness of the proposed algorithm.
Physically Based Modeling of Ice with Bubbles
(The Eurographics Association, 2008) Madrazo, Carlos; Okada, Minoru; Katerina Mania and Eric Reinhard
Bubbles are an important characteristic that determine the appearance of ice. In this paper the authors propose a strategy in order to construct geometric representations of ice that integrates bubbles in an ice cube and visualize them. Bubble characteristics depend on the velocity of ice formation and levels of air concentration of water that in this paper are determined by simulating ice and bubble formation processes together. Simplified physics of heat transfer and a level set method are used in order to evolve the ice-water interface and a simplified model of bubbles as spheres is discussed. Experimental result shows that the shape of ice during formation resembles the one of actual ice. The algorithm has a potential to include more complex physics for better accuracy
Theory and Methods of Light-Field Photography
(The Eurographics Association, 2008) Georgiev, Todor; Lumsdaine, Andrew; Maria Roussou and Jason Leigh
Computational photography is based on capturing and processing discrete representations of all the light rays in the 3D space. Compared to conventional photography, which captures 2D images, computational photography captures the entire 4D "lightfield", i.e., the full 4D radiance. To multiplex the 4D radiance onto conventional 2D sensors, light-field photography demands sophisticated optics and imaging technology. At the same time, 2D image creation is based on creating 2D projections of the 4D radiance. This tutorial presents light-field analysis in a rigorous mathematical way, which often leads to surprisingly direct solutions. The mathematical foundations will be used to develop computational methods for lightfield processing and image rendering, including digital refocusing and perspective viewing. While emphasizing theoretical understanding, we also explain practical approaches and engineering solutions. As part of the course, we will demonstrate a number of working light-field cameras that implement different methods for radiance capture, including the microlens approach of Lippmann and the plenoptic camera; the MERL mask enhanced camera; the Adobe lens-prism camera; and a new camera using a "mosquito net" mask. Various computational techniques for digital refocusing and rendering will also be demonstrated, including Ng's Fourier slice algorithm and the MERL heterodyned light-field approach.
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.
Removing Artifacts Due To Frequency-Domain Processing of Light-Fields
(The Eurographics Association, 2008) Intwala, Chintan; Georgeiv, Todor; Katerina Mania and Eric Reinhard
In previous works, light-field capture has been analyzed in spatio-angular representation. A light-field camera samples the optical signal within a single photograph by multiplexing the 4D radiance onto the physical 2D surface of the sensor. Besides sampling the light field spatially, methods have been developed for multiplexing the radiance in the frequency domain by optically mixing different spatial and angular frequency components. The mathematical method for recovering the multiplexed spatial and angular information from the frequency representation is very straightforward. However, the results are prone to lots of artifacts due to limitations inherent to frequency-domain processing of images. In this paper, we try understand the characteristics of these artifacts. Furthermore, we study the effect and sources of artifacts that affect the quality of the results and present various methods for the removal of artifacts.
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.
eNVyMyCar: a Multi-player Car Racing Game for Teaching Computer Graphics
(The Eurographics Association, 2008) Ganovelli, Fabio; Corsini, Massimiliano; Steve Cunningham and Lars Kjelldahl
The development of a computer game is widely used as a means to convey Computer Sciences concepts. There are several reasons for that: it stimulates creativity, it provides an immediate sense of achievement when the code works, it typically covers all the aspects of an introductory course, it is easy to find ideas just looking around. In this paper we present NVMC (eNVy My Car), a framework for collaborative/competitive development of a computer game, and report the experience in using it in two Computer Graphics courses held in the year 2007 by the authors. We developed a multiplayer car racing game where the student is only asked to implement the rendering of the scene, while all the other aspects, communication and synchronization are implemented in the framework and transparent to the developer. The novelty of our framework is that all the clients on-line are able to see the views provided by the other clients, which serves to motivate the students to improve their work by comparing it with the other clients, as a means to pick up ideas from the others and finally to show off with their classmates.
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.

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