Computer Graphics
TU Braunschweig


Talk Image/Video error metrics

02.03.2009 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Kai Berger

When the subjective quality of e.g. compressed image or video data is to be approximated by an objective metric, popular formulae such as MSE or PSNR appear to do the job well. However, in several scenarios these standard formulae don't correspond subjective quality evaluations. In this talk three different types of image/video quality assessment methods are presented. Exemplaric algorithms for these types will be compared to MSE/PSNR.

Talk Multi-View Stereo algorithms - overview and comparison

23.02.2009 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Christian Lipski

Multi-View Stereo reconstruction algorithms are a very active field in computer graphics and computer vision. Seitz et al. have established multi-view data sets with known ground truth as a basis for evaluation and comparison ( We took a closer look at the current top performers, evaluate approaches with our own data sets and identify cases where these approaches fail. Possible solutions are presented and discussed.

Talk Space-time Surface Reconstruction Using Incompressible Flow

16.02.2009 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Christian Linz

We introduce a volumetric space-time technique for the reconstruction of moving and deforming objects from point data. The output of our method is a four-dimensional generalized cylinder in space-time, made up of spatial slices, each of which is a three-dimensional solid bounded by a watertight manifold. The motion of the object is described as an incompressible flow of material through time. We optimize the flow so that the distance material moves from one time frame to the next is bounded, the density of material remains constant, and the object remains compact. This formulation overcomes deficiencies in the acquired data, such as persistent occlusions, errors, and missing frames. We demonstrate the performance of our flow-based technique by reconstructing coherent sequences of watertight models from incomplete scanner data.

Talk Pixel-exact shadow-mapping based on GPU ray tracing using CUDA

06.02.2009 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Rolf Krämer

Die stetig fortschreitende Entwicklung von Grafikkarten Prozessoren (GPUs) eröffnen neue Möglichkeiten die Standard-Grafikpipeline zu durchbrechen und generellere Konzepte auf der GPU umzusetzen (GPGPU). Gerade auch in der gängigen Grafikdarstellung mittels Rasterisierung ist die Erweiterung sinnvoll, da man in vielen Bereichen an seine Grenzen gestossen zu sein scheint. Ein Beispiel dafür ist die Darstellung von harten Schatten. Gängige echtzeitfähige Ansätze wie ShadowMaps können für Aliasing-Artefakte an den Schattenkanten sorgen, welche unangenehm auffallen. In dieser Arbeit wurde ein Hybrid-System entworfen, welches diese Nachteile umgeht und pixelgenaue Schatten berechnet. Dafür werden die Primärstrahlen und das Shading mittels gewöhnlicher Standardpipeline berechnet, während die Schatten durch einen GPU-unterstützten Ray Tracer berechnet werden, welcher unter Zuhilfenahme von NVidias CUDA entworfen wurde.

Talk Unterstützung der visuellen Analyse hochdimensionaler Daten durch klassenbasierte Projektionsgütemas

30.01.2009 13:00
Informatikzentrum, Hörsaal 160

Speaker(s): Andrada Tatu

Zunehmende Dimensionalität und anwachsendes Datenvolumen erfordern effektive Explorationstechniken, um dem Benutzer Einblicke in Muster in den Daten zu ermöglichen. Bei der visuellen Analyse müssen dabei hochdimensionale Daten auf niedrigdimensionale Sichten projiziert werden. Es gibt verschiedene Ansätze um niedrigdimensionale Darstellungen aus hochdimensionalen Daten zu erzeugen und diese zu bewerten. In dieser Arbeit werden Verfahren vorgestellt um gute Projektionen hochdimensionaler Daten zu erhalten. Es werden dazu Konzepte präsentiert um lineare und nichtlineare Projektionen zu finden, die an realen Daten getestet werden. Kern der Arbeit ist dabei mit Hilfe von achsenparallelen und nicht-achsenparallelen Projektionen Dimensionen und Unterräume der Daten zu finden, die die Datenstruktur am besten darstellen. Zur Bewertung der Projektionen werden Projektionsgütemasse vorgestellt, welche im Gegensatz zu existierenden Verfahren die Dichteverteilung der Daten berücksichtigen. Vorteil dieser Methode ist es, dass nicht nur Beziehungen zwischen zwei Dimensionen, sondern auch zwischen mehreren Dimensionen gefunden werden.

Talk Computational Vision for Graphics

26.01.2009 14:00
Informatikzentrum, Seminarraum G30

Speaker(s): Oliver Grau

Talk Imperfect Shadow Maps for Efficient Computation of Indirect Illumination

26.01.2009 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Benjamin Meyer

We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps - low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

Talk Unwrap Mosaics: a new representation for video editing

12.01.2009 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Anita Sellent

Though photoediting is very common today, extending such editing task on video is still very tedious work. In their SIGGRAPH 2008 paper Rav-Acha et al. present a new way to edit uncalibrated monocular video footage. The basic idea of the approach is to represent a video sequence as a 2D mosaic accompanied by a mapping from the mosaic to the frames of the video and an occlusion map. Editing operations can than be performed directly on the mosaic and resomposited with the original video. In this colloquium, ideas and details necessary for the determination of the mosaic, mapping and occlusion map are disscussed.

Talk Tomographic Reconstruction of Gas Flows in the Presence of Occluders

15.12.2008 13:30
Informatikzentrum, Seminarraum G30

Speaker(s): Kai Berger

Nowadays, non-stationary and time-varying gas flows, for example the heated air above a camping stove, can be captured and tomographically reconstructed by making use of the Background-oriented Schlieren (BOS) method. In this method a high-frequency noise pattern, for example generated by wavelet noise, is placed behind the volume under observation and the per pixel deflections in the input image caused by the varying refractive index of the gas volume is measured. These deflections, which can be computed by optical flow methods, can be integrated to a tomographically consistent refractional index volume by solving an equation system for 3D deflection vectors and integrating them, e.g. by a Poisson-integration.

However, when the interaction of such a gas with occluding objects is examined, for example when a marshmellow is moved above the camping stove, different alterations to the existing tomographic reconstruction algorithm have to be applied. In this talk the existing method is introduced and the occuring problems with occluding objects are stated. Afterwards, alterations to the stages of this method are proposed and evaluated.

Talk The OMNI Display: Using a Large Peripheral Display for Workgroup Awareness in Distributed Groups

05.12.2008 14:00
Informatikzentrum, Seminarraum G30

Speaker(s): Maryam Mustafa

The initiation of interaction in face-to-face work environments is a gradual process and takes place in a rich information landscape of awareness and social signals. This gradual approach to interaction is missing from most online messaging systems. In this talk I will be discussing a prototype system called the Open Messenger Notification and Interaction (OMNI) display that uses a projected peripheral display to provide dynamic, real-time awareness information using a peripheral display in the architectural space of the user in ways that are both rich and subtle. OMNI has been designed to use people's natural abilities to absorb information in the periphery without being distracted from their primary task. OMNI accomplishes this by using motion and color to subtly provide several types of information about online contacts. I will discuss our approach to capturing and presenting relevant information for awareness of the surroundings, facilitating interaction and creating an online collaborative environment.

Talk Exhaustive visual search for information in multi-dimensional data-sets

05.12.2008 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Georgia Albuquerque, Martin Eisemann

Goal of this research project is to develop and evaluate a fundamentally new approach to exhaustively search for, and interactively characterize any non-random mutual relationship between attribute dimensions in general data sets. To be able to systematically consider all possible attribute combinations, we propose to apply image analysis to visualization results in order to automatically pre-select only those attribute combinations featuring non-random relationships. To characterize the found information and to build mathematical descriptions, we rely on interactive visual inspection and visualization-assisted interactive information modeling. This way, we intend to discover and explicitly characterize all information implicitly represented in unbiased sets of multi-dimensional data points.

Talk Shape, neue 3D Methoden für astrophysikalische Modelle

03.11.2008 17:00
Informatikzentrum, Hörsaal 160

Speaker(s): Wolfgang Steffen

Für die meisten Fragen waren astrophysikalische 3D Simulationen mit angemessener Auslösung bis vor einigen Jahren zu aufwendig. Andererseits hat sich von der Beobachtungsseite her in den letzten Jahrzehnten klar gezeigt, dass die Struktur vieler astrophysikalischer Objekte intrinsisch 3D ist. Wie diese Formen zustande kommen scheint tief in der offensichtlich nur teilweise verstandenen Entwicklungsgeschichte der Objekte zu stecken. Dies gilt insbesondere für planetarische Nebel, ein Entwicklungsstadium für sonnenähnliche Sterne. Die Notwendigkeit, die 3D-Struktur dieser Nebel zu kennen, hat uns dazu verleitet, ein neues Konzept der Strukturmodellierung in die Astrophysik einzuführen: Interaktives Modellieren, wie es in der Graphikindustrie üblich ist, mit dem Extra der Geschwindigkeit als wissenschaftliche Diagnostik. "Shape" ist das Ergebnis dieser Entwicklung und ist bisher das einzige Programmpaket seiner Art.

Talk Motion Effects - Bewegungseffekte in Bildern und Videos

22.10.2008 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Martin Fiebig

"Ein Bild sagt mehr als 1000 Worte". Um die Aussage eines Bildes noch weiter hervorzuheben, ist es oft hilfreich nicht photorealistische (NPR) Effekte zu verwenden (wie z.B. Speedlines). In diesem Vortrag wird vorgestellt, wie mit dem bestehenden Interpolationsverfahren des CG-Instituts nicht photorealistische Effekte erzeugt werden können. Es werden verschiedene Algorithmen und Verfahren präsentiert.

Talk Korrektur des zeitlichen Versatzes zwischen mehreren unsynchronisierten Videosequenzen einer dynamis

22.10.2008 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Markus Lorenz

Wird eine dynamische Szene zeitgleich mit mehreren Kameras gefilmt, sind die Videosequenzen meist asynchron. Dies resultiert aus einem zeitversetzten Aufnahmestart. Für viele moderne Verfahren der Computergraphik ist jedoch unabdingbar, diesen Zeitversatz auf einfache Art und Weise bestimmen zu können. In diesem Vortrag wird die Umsetzung von Algorithmen zur Versatzbestimmung vorgestellt.

Talk SIMD-Raytracing with the Single Slab Hierarchy

04.09.2008 14:00
Informatikzentrum, Seminarraum G30

Speaker(s): Christian Woizischke

During the last years ray tracing became more and more important again in the field of computer graphics. Faster algorithms, better data structures and faster PCs allow for interactive or even real-time ray tracing. The biggest gain in speed is achieved due to acceleration data structures such as Bounding Volume Hierarchies (BVH) or kd-Trees. In this talk a new acceleration data structure is presented, the Single Slab Hierarchy. The Single Slab Hierarchy is similar to a BVH but represents every node with just one slab. Even though information is lost due to this, one can calculate a conservative hit/miss with a ray, using an active ray interval. This has several benefits. First, traversal becomes very similar to kd-Trees and memory requirements are reduced to 25 percent compared to a standard BVH, which is very beneficial if complex models are to be rendered.

Talk Astrophysical gaseous nebulae: 1D and 3D models

01.04.2008 15:00
Informatikzentrum, Hörsaal 160

Speaker(s): Christophe Morisset

The interstellar medium is the counterpart of the stars in the cycle of matter evolution in the Universe. New stars are build from giant gaseous clouds and dead stars are giving back to the interstellar medium new elements synthesized during their life. Understanding the physics of such gaseous nebulae is a key to our knowledge of the chemical evolution of our Universe. I will present in this talk the computational tools used to model such gaseous nebulae, especially the 3D photoionization codes, and some applications to HII regions and Planetary Nebulae.

Talk Computer - Bilder

19.12.2007 17:00
Aula, Haus der Wissenschaft

Speaker(s): Marcus Magnor

Antrittsvorlesung Prof. Marcus Magnor.

Computer - Bilder

Talk Perceptual Graphics: The Integration of Perception Research and Computer Graphics Research

15.05.2007 15:00
Informatikzentrum, Hörsaal 160

Speaker(s): Douglas Cunningham

Real visual scenes specify an enormous amount of perceptually and behaviorally relevant information. Perception science investigates how the sensory systems of humans and animals extract, represent, and process such information. Computer graphics focuses on the visual simulation of such information, traditionally emphasizing a high degree of realism. Although these two fields have developed independently, they address similar fundamental problems and provide complementary methods for their solution. Furthermore, it is becoming increasingly apparent that specific research questions in either discipline cannot be solved without methods from the other. The fusion of these two complementary approaches not only helps to overcome the inherent limits of each approach, but also opens up entire new realms of scientific inquiry. This integrated approach is referred to as Perceptual Graphics. In this talk, I will provide an overview of how perception and computer graphics can help one another, both symbiotically and in a truly integrated fashion. I will also provide a brief look at several examples of current Perceptual Graphics research.

Talk High Dynamic Range Imaging and Display

06.03.2007 14:00
Informatikzentrum, Seminarraum G30

Speaker(s): Wolfgang Heidrich

The human visual system's ability to process wide ranges of intensities by far exceeds the capabilities of current imaging systems. Both cameras and displays are currently limited to a dynamic range (contrast) of between 300:1 to 1,000:1, while the human visual system can process a simultaneous dynamic range of 50,000:1 or more, and can adapt to a much larger range.

High-dynamic-range (HDR) imaging refers to the capture, processing, storage, and display of images with significantly improved contrast and brightness compared to the conventional imaging pipeline. This new HDR imaging pipeline is designed to match the power of the human visual system. HDR displays significantly improve the sense of realism and immersion when showing both real and synthetic HDR imagery. Likewise, HDR cameras are able to take images without saturation under difficult lighting situations. The additional information captured in both extremely bright and extremely dark regions is useful as an input for HDR displays, but also for machine vision applications.

In this talk, I will summarize the results of a multi-disciplinary research effort to create the first true HDR display. This work is a collaboration of multiple departments at The University of British Columbia, and a spin-off company called Brightside Technologies. I will provide an overview of current research activities, with a focus on computational problems.

Talk Eikonal Rendering

22.12.2006 11:00
Informatikzentrum, Seminarraum G30

Speaker(s): Ivo Ihrke

In this talk, I present an interactive rendering method for refractive objects. The refractive index is allowed to vary continouosly, and total reflection is taken into account. The method is based on set of ordinary differential equations that are derived from the eikonal equation, the main postulate of ray optics. This set of equation allows for ray casting of bent light rays with the complexity of a particle tracer.

Talk A Framework for Holographic Scene Representation

19.10.2006 13:00
Informatikzentrum, Seminarraum G30

Speaker(s): Gernot Ziegler

At ETH we developed a framework for holographic representation and display of graphics objects. As opposed to traditional graphics representations, our approach reconstructs the light wave reflected or emitted by the original object directly from the underlying digital hologram. Our novel holographic graphics pipeline consists of several stages including the digital recording of a full-parallax hologram, the reconstruction and propagation of its wavefront, and rendering of the final image onto conventional, framebuffer-based displays. The required view-dependent depth image is computed from the phase information inherently represented in the complex-valued wavefront. Our model also comprises a correct physical modelling of the camera taking into account optical elements, such as lens and aperture. It thus allows for a variety of effects including depth of field, diffraction, interference and features built-in anti-aliasing. A central feature of our framework is its seamless integration into conventional rendering and display technology, which enables us to elegantly combine traditional 3D object or scene representations with holograms.

Talk Gaussian curvature on polyhedral surfaces

22.08.2006 14:00
Informatikzentrum, Seminarraum G30

Speaker(s): Anita Sellent

The Gaussian curvature of a regular surface is a well-known term in differential geometry; there are even several equivalent ways to define it. Gauss himself defined this curvature via the normal image. In the presentation this definition is transferred to polyhedral surfaces: Though the procedure is obvious for convex vertices it causes some difficulties for non-convex vertices. A method to calculate the normal image for some of the non-convex vertices is presented which on the one hand confirms the angle-deficit as polyhedral Gaussian curvature and on the other hand bears further information on the vertices. In conclusion some of the fundamental theorems for the continuous Gaussian curvature can be affirmed for its polyhedral analogue.

Talk Boosting Restricted to Integer Lattices

18.07.2006 14:00
Informatikzentrum, Seminarraum G30

Speaker(s): Dirk Breitenreicher

When classifying a set of samples into various classes in most cases one highly complex optimization problem has to be solved. A boosting approach, in contrast, is able to determine multiple weak learners such that their combination is as accurate as the single, strong classification rule. Often these weak learners are easier to obtain than the solution of the complex optimization problem. However, finding weak learners that can be used for boosting is a not trivial task. Obtaining multiple weak learning rules may also require a lot of time and memory. Classifying on integer lattices can address this problem. When using classifiers on integer lattices each weak learner is build up on integer variables exclusively. This causes that the training and the evaluation time as well as the required memory decreases dramatically in most cases.

Talk Automatic Creation of Object Hierachies for Ray tracing of Dynamic Scenes

26.04.2006 14:00
Informatikzentrum, Seminarraum G30

Speaker(s): Martin Eisemann

Ray tracing acceleration techniques most often consider only static scenes, neglecting the processing time needed to build the acceleration data structure. With the development of interactive ray tracing systems, this reconstruction time becomes serious bottleneck if concerned with dynamic scenes. I am going to describe two strategies for efficient updating of bounding volume hierarchies (BHV) for scenarios with arbitrarily moving objects. The first exploits spatial locality in the object distribution for faster reinsertion of the moved objects. The second allows insertion and deletion of objects at almost constant time by using a hybrid system, which combines benefits from both spatial subdivision and BHVs. Depending on the number of moving objects, the algorithms adjust a dynamic BHV six to one hundred times faster than it would take to rebuild the complete hierarchy, while rendering times of the resulting hierarchy remains almost untouched.