Methods for transform, analysis and rendering of complete light representations
(Ahrenberg, Lukas, 2007-07-16) Ahrenberg, Lukas
Recent advances in digital holography, optical engineering and computer graphics have opened up the possibility of full parallax, three dimensional displays. The premises of these rendering systems are however somewhat different from traditional imaging and video systems. Instead of rendering an image of the scene, the complete light distribution must be computed. In this thesis we discuss some different methods regarding processing and rendering of two well known full light representations: the light field and the hologram. A light field transform approach, based on matrix optics operators, is introduced. Thereafter we discuss the relationship between the light field and the hologram representations. The final part of the thesis is concerned with hologram and wave field synthesis. We present two different methods. First, a GPU accelerated approach to rendering point-based models is introduced. Thereafter, we develop a Fourier rendering approach capable of generating angular spectra of triangular mesh models.
Selected Quality Metrics for Digital Passport Photographs
(Gonzalez Castillo, 12.12.2007) Gonzalez Castillo, Oriana Yuridia
Passbilder spielen eine wichtige Rolle bei der Identifizierung von Personen. Da die Personenerkennunggegenwärtig immer mehr an Bedeutung gewinnt und die Genauigkeit derErkennung einen großen Einfluß auf verschiedene Sicherheitsaspekte haben kann, ist die guteQualität von Passbildern unerläßlich. Gegenwärtig erfolgt die Bestimmung der Qualität durchPersonen. I ist daher geprägt von der persönlichen Wahrnehmung und unterliegt damit subjektivenund nicht standardisierten Kriterien. Zwar existieren bereits Algorithmen, die zurautomatischen Qualitätsbestimmung digitaler Fotos benutzt werden, diese sind aber nichtspeziell auf Passbilder abgestimmt. Das bedeutsamste Dokument, das sich mit der Definitionvon Kriterien zur Bestimmung der Qualität digitaler Passbilder beschäftigt trägt den Titel
Reconstruction and Rendering of Time-Varying Natural Phenomena
(Ihrke, 2007-05-21) Ihrke, Ivo
While computer performance increases and computer generated images getever more realistic, the need for modeling computer graphics content is becoming stronger. To achieve photo-realism, detailed scenes have to be modeled, often with a significant amount of manual labour. Interdisciplinary research combining the fields of Computer Graphics, Computer Vision, and Scientific Computing has led to the development of (semi-)automatic modeling tools freeing the user of labour-intensive modeling tasks.The modeling of animated content is especially challenging. Realistic motion is necessary to convince the audience of computer games, movies with mixed reality content, and augmented reality applications. The goal of this thesis is to investigate automated modeling techniques for time-varying natural phenomena. The results of the presented methods are animated, three-dimensional computer models of fire, smoke and fluid flows.
Geometric Computing in Computer Graphics and Robotics using Conformal Geometric Algebra
(Hildenbrand, Dietmar, Dec 2006) Hildenbrand, Dietmar
In computer graphics and robotics a lot of different mathematical systems like vector algebra, homogenous coordinates, quaternions or dual quaternions are used for different applications. Now it seems that a change of paradigm is lying ahead of us based on Con- formal Geometric Algebra unifying all of these different approaches in one mathematical system. Conformal Geometric Algebra is a very powerful mathematical framework. Due to its geometric intuitiveness, compactness and simplicity it is easy to develop new algorithms. Algorithms based on Conformal Geometric Algebra lead to enhanced quality, a reduction of development time, better understandable and better maintainable solutions. Often a clear structure and greater elegance results in lower runtime performance. However, it will be shown that algorithms based on Conformal Geometric Algebra can even be faster than conventional algorithms. The main contribution of this thesis is the geometrically intuitive and - nevertheless - efficient algorithm for a computer animation application, namely an inverse kinemat- ics algorithm for a virtual character. This algorithm is based on an embedding of quaternions in Conformal Geometric Algebra. For performance reasons two optimiza- tion approaches are used in a way to make the application now three times faster than the conventional solution. With these results we are convinced that Geometric Computing using Confor- mal Geometric Algebra will become more and more fruitful in a great variety of applications in computer graphics and robotics.
Realistic Rendering and Reconstruction of Astronomical Objects and an Augmented Reality Application for Astronomy
(Lintu, Andrei, 2007-12-07) Lintu, Andrei
These days, there is an ever increasing need for realistic models,renderings and visualization of astronomical objects to be used inplanetarium and as a tool in modern astrophysical research. One of themajor goals of this dissertation is to develop novel algorithms forrecovering and rendering 3D models of a specific set of astronomicalobjects. We first present a method to render the color and shape ofthe solar disc in different climate conditions as well as fordifferent height to temperature atmospheric profiles. We then presenta method to render and reconstruct the 3D distribution of reflectionnebulae. The rendering model takes into account scattering andabsorption to generate physically realistic visualization ofreflection nebulae. Further, we propose a reconstruction method foranother type of astronomical objects, planetary nebulae. We alsopresent a novel augmented reality application called the augmentedastronomical telescope, tailored for educational astronomy. Thereal-time application augments the view through a telescope byprojecting additional information such as images, text and videorelated to the currently observed object during observation. Allmethods previously proposed for rendering and reconstructingastronomical objects can be used to create novel content for thepresented augmented reality application.
Perception-inspired Tone Mapping
(Krawczyk, 2007-11-30) Krawczyk, Grzegorz M.
The display of high dynamic range images and video requires a tonemapping algorithm to depict their original appearance on existing display devices whose capabilities in terms of dynamic range are insufficient. The insightful application of knowledge about human visual system can assure high fidelity of depiction in such an algorithm. In this thesis, we design new tone mapping models and improve existing algorithms by an informed use of human perception to provide a high fidelity depiction of high dynamic range. We develop a real-time tone mapping solution which reproduces the subjective appearance of dynamic HDR contents by accounting for perceptual effects that significantly contribute to the appearance of natural scenes. We design a computational model of lightness perception that can be applied to high quality tone mapping for static images to reproduce their original HDR appearance in terms of lightness. We identify common distortions typical to tone mapping which may hinder the comprehension of image contents, we design appropriate metrics to measure the perceived magnitude of these distortions and evaluate existing tone mapping algorithms accordingly. To compensate for observed distortions, we introduce a method which improves the tone mapping results beyond numerically optimized solution by using techniques strongly based on perception of contrasts. Presented solutions can be efficiently integrated in varied HDR applications including photography, playback of HDR video, image synthesis, light simulations, predictive rendering, and computer games.</p>
New editing techniques for video post-processing
(Scholz, Volker, 2007-05-21) Scholz, Volker
This thesis contributes to capturing 3D cloth shape, editing cloth texture and altering object shape and motion in multi-camera and monocular video recordings. We propose a technique to capture cloth shape from a 3D scene flow by determining optical flow in several camera views. Together with a silhouette matching constraint we can track and reconstruct cloth surfaces in long video sequences. In the area of garment motion capture, we present a system to reconstruct time-coherent triangle meshes from multi-view video recordings. Texture mapping of the acquired triangle meshes is used to replace the recorded texture with new cloth patterns. We extend this work to the more challenging single camera view case. Extracting texture deformation and shading effects simultaneously enables us to achieve texture replacement effects for garments in monocular video recordings. Finally, we propose a system for the keyframe editing of video objects. A color-based segmentation algorithm together with automatic video inpainting for filling in missing background texture allows us to edit the shape and motion of 2D video objects. We present examples for altering object trajectories, applying non-rigid deformation and simulating camera motion.
Interactive Vegetation Rendering
(Mantler, Mar 2007) Mantler, Stephan
In der Computergrafik ist die interaktive Darstellung von Pflanzen nachwie vor ein bedeutendes Problem. Deren organische Struktur besitzt oftmalseine sehr große geometrische Komplexität, die nur schlecht mit herkömmlichenVerfahren reduziert werden kann. Diese Arbeit präsentiertneue Lösungsansätze sowohl für die Darstellung individueller Pflanzenals auch für ganze Landschaften.Zur Darstellung einzelner Pflanzen wurde eine Erweiterung des BillboardCloud Verfahrens zur extremen Vereinfachung von polygonalen Modellenentwickelt. Dieses Verfahren reduziert beliebig komplexe Objekteauf sehr wenige Polygone; allerdings ist das Ergebnis oft nur für dieBetrachtung aus größeren Distanzen sinnvoll. Die von uns entwickeltenDisplacement Mapped Billboard Clouds erlauben eine stark verbesserteDarstellungsqualität, sodass die reduzierten Modelle über einen deutlichgrößeren Bereich angezeigt werden können.Weiters werden für individuelle Pflanzen oft punktbasierte Darstellungsmethodenverwendet. Ein in dieser Arbeit vorgestelltes Verfahrenerlaubt ein rasches, approximatives Erfassen der sichtbaren Punktmenge.In weiterer Folge kann diese reduzierte Punktmenge zur Darstellungverwendet werden, wodurch eine deutlich schnellere Darstellung bei nahezugleichbleibender Bildqualität erzielt wird.Für das interaktive Rendering ganzer Landschaften wurde ein Verfahrenentwickelt, das auf Displacement Mapping Shader setzt um existierendeTerrainmodelle mit Vegetation darzustellen. Zusätzlich zu dem eigentlichenVerfahren werden auch Probleme bei der Handhabung sehrgroßer Gebiete diskutiert und entsprechende Lösungsansätze vorgestellt.Als Beispiel für eine global scale Applikation wurde das Verfahren indem von der NASA entwickelten GeoinformationssystemWorldWind integriert.Darüber hinaus wird in dieser Arbeit ein erweiterter Ansatz zur Verwendungvon early-Z Beschleunigungsverfahren in Shadern präsentiert,für die dies derzeit nicht möglich ist. Darüber hinaus präsentieren wirein zweistufiges Verfahren zur Gültigkeit von dynamisch erzeugten Impostorsund Methoden zur zeitkritischen gemeinsamen Darstellung vondiskreten und kontinuierlichen LOD-Modellen. - Vegetation poses a significant problem to computer graphics because thegeometric complexity of plants does not lend itself very well to traditionalsimplification approaches. This thesis presents new algorithmsthat address these issues at different scales, for rendering individual plantsas well as entire landscapes.For individual plants we introduce Displacement Mapped BillboardClouds, an extended version of the billboard cloud extreme simplificationapproach. Billboard clouds have been successfully used to reduce thegeometric complexity of highly detailed models to a few planes, howeverthe resulting models are often unsuitable for viewing at closer distances.The presented extension exploits shaders to improve the visual qualityof the resulting models.Also, a method is introduced for quickly determining approximatevisible sets for point clouds, which are often used for rendering individualplants. Approximate visible sets allow a significant reduction in thenumber of primitives to be rendered with only very little impact on visualquality.For entire landscapes, displacement mapping shaders are explored toenhance existing terrain models with vegetation. We also address theissues involved with applying such techniques at a global scale, andpresent the integration of our method in the open source World Windgeospatial viewer.Furthermore, we propose a way to enable early-Z acceleration methodson the GPU for shaders where this is not yet possible, and discuss thehandling of level of detail validity and criteria for time-critical renderingof discrete and continuous levels of detail.
Numerical and variational aspects of mesh parameterization and editing
(Zayer, Rhaleb, 2007-09-17) Zayer, Rhaleb
A surface parameterization is a smooth one-to-one mapping between the surface and a parametric domain. Typically, surfaces with disk topology are mapped onto the plane and genus-zero surfaces onto the sphere. As any attempt to flatten a non-trivial surface onto the plane will inevitably induce a certain amount of distortion, the main concern of research on this topic is to minimize parametric distortion. This thesis aims at presenting a balanced blend of mathematical rigor and engineering intuition to address the challenges raised by the mesh parameterization problem. We study the numerical aspects of mesh parameterization in the light of parallel developments in both mathematics and engineering. Furthermore, we introduce the concept of quasi-harmonic maps for reducing distortion in the fixed boundary case and extend it to both the free boundary and the spherical case. Thinking of parameterization in a more general sense as the construction of one or several scalar fields on a surface, we explore the potential of this construction for mesh deformation and surface matching. We propose an ''on-surface parameterization'' for guiding the deformation process and performing surface matching. A direct harmonic interpolation in the quaternion domain is also shown to give promising results for deformation transfer.

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