Visual Fixation for 3D Video Stabilization

Visual fixation is employed by humans and some animals to keep a specific 3D location at the center of the visual gaze. Inspired by this phenomenon in nature, this paper explores the idea to transfer this mechanism to the context of video stabilization for a handheld video camera. A novel approach is presented that stabilizes a video by fixating on automatically extracted 3D target points. This approach is different from existing automatic solutions that stabilize the video by smoothing. To determine the 3D target points, the recorded scene is analyzed with a stateof- the-art structure-from-motion algorithm, which estimates camera motion and reconstructs a 3D point cloud of the static scene objects. Special algorithms are presented that search either virtual or real 3D target points, which back-project close to the center of the image for as long a period of time as possible. The stabilization algorithm then transforms the original images of the sequence so that these 3D target points are kept exactly in the center of the image, which, in case of real 3D target points, produces a perfectly stable result at the image center. Furthermore, different methods of additional user interaction are investigated. It is shown that the stabilization process can easily be controlled and that it can be combined with state-of-theart tracking techniques in order to obtain a powerful image stabilization tool. The approach is evaluated on a variety of videos taken with a hand-held camera in natural scenes.

Cosine Lobe Based Relighting from Gradient Illumination Photographs

We present an image-based method for relighting a scene by analytically fitting cosine lobes to the reflectance function at each pixel, based on gradient illumination photographs. Realistic relighting results for many materials are obtained using a single per-pixel cosine lobe obtained from just two color photographs: one under uniform white illumination and the other under colored gradient illumination. For materials with wavelength-dependent scattering, a better fit can be obtained using independent cosine lobes for the red, green, and blue channels, obtained from three achromatic gradient illumination conditions instead of the colored gradient condition. We explore two cosine lobe reflectance functions, both of which allow an analytic fit to the gradient conditions. One is non-zero over half the sphere of lighting directions, which works well for diffuse and specular materials, but fails for materials with broader scattering such as fur. The other is non-zero everywhere, which works well for broadly scattering materials and still produces visually plausible results for diffuse and specular materials. We also perform an approximate diffuse/specular separation of the reflectance, and estimate scene geometry from the recovered photometric normals to produce hard shadows cast by the geometry, while still reconstructing the input photographs exactly.

Method of collaborative detection of autonomous transport vehicles based on laser rangefinder data

To master changing performance demands, autonomous transport vehicles are deployed to make inhouse material flow applications more flexible. The socalled cellular transport system consists of a multitude of small scale transport vehicles which shall be able to form a swarm. Therefore the vehicles need to detect each other, exchange information amongst each other and sense their environment. By provision of peripherally acquired information of other transport entities, more convenient decisions can be made in terms of navigation and collision avoidance. This paper is a contribution to collective utilization of sensor data in the swarm of cellular transport vehicles.

Integration von 3D-Kamerasystemen am Gabelstapler

Dieser Beitrag beschreibt die Integration von laufzeitmessenden 3D Kamerasystemen in die Gabelzinkenspitzen eines Flurförderzeugs. Mit Hilfe der integrierten Kameras und deren ausgewerteter Aufnahmen wurde ein Assistenzsystem für die Handhabung von Ladungsträgern realisiert, das dem Fahrer des Flurförderzeugs Verfahrempfehlungen für die Optimierung der Relativposition zwischen Gabelzinken und Ladungsträger bzw. Lagerplatz ausgibt. Neben der Vorstellung der verwendeten Kamera-Hardware und der Integration am Fahrzeug wird auch der Ablauf der Bildverarbeitung beschrieben.

Bitmap Movement Detection: HDR for Dynamic Scenes

Exposure Fusion and other HDR techniques generate well-exposed images from a bracketed image sequence while reproducing a large dynamic range that far exceeds the dynamic range of a single exposure. Common to all these techniques is the problem that the smallest movements in the captured images generate artefacts (ghosting) that dramatically affect the quality of the final images. This limits the use of HDR and Exposure Fusion techniques because common scenes of interest are usually dynamic. We present a method that adapts Exposure Fusion, as well as standard HDR techniques, to allow for dynamic scene without introducing artefacts. Our method detects clusters of moving pixels within a bracketed exposure sequence with simple binary operations. We show that the proposed technique is able to deal with a large amount of movement in the scene and different movement configurations. The result is a ghost-free and highly detailed exposure fused image at a low computational cost.

A Comparative Evaluation of Three Skin Color Detection Approaches

Skin segmentation is a challenging task due to several influences such as unknown lighting conditions, skin colored background, and camera limitations. A lot of skin segmentation approaches were proposed in the past including adaptive (in the sense of updating the skin color online) and non-adaptive approaches. In this paper, we compare three skin segmentation approaches that are promising to work well for hand tracking, which is our main motivation for this work. Hand tracking can widely be used in VR/AR e.g. navigation and object manipulation. The first skin segmentation approach is a well-known non-adaptive approach. It is based on a simple, pre-computed skin color distribution. Methods two and three adaptively estimate the skin color in each frame utilizing clustering algorithms. The second approach uses a hierarchical clustering for a simultaneous image and color space segmentation, while the third approach is a pure color space clustering, but with a more sophisticated clustering approach. For evaluation, we compared the segmentation results of the approaches against a ground truth dataset. To obtain the ground truth dataset, we labeled about 500 images captured under various conditions.

Dreidimensionale Bewegungserfassung mit Consumer-Highspeedkameras: Eine Systementwicklung unter besonderer Berücksichtigung der Messunsicherheit

Schwerpunkt dieser Arbeit ist die Entwicklung und der Test eines auf Consumer-Highspeedkameras basierenden Bewegungserfassungssystems. Consumer-Kameras sind flexibler einsetzbar als kommerzielle Bewegungserfassungssysteme, zugleich kostengünstiger und werden daher oft in der sportwissenschaftlichen Forschung verwendet. Durch ihren Einsatz entstehen jedoch prinzipbedingt höhere Messunsicherheiten, deren Bestimmung in der vorliegenden Arbeit ein besonderer Stellenwert eingeräumt wird. Nach einem Überblick über aktuelle Bewegungserfassungssysteme und deren Genauigkeiten folgt eine Betrachtung der Messunsicherheit aus metrologischer Perspektive. Anschließend werden die Prozesse der Bilderfassung bei digitalen Consumer-Kameras sowie die zur Modellierung des Kameraabbildungsverhaltens notwendigen Parameteridentifikationsmethoden dargestellt. Diese reichen vom häufig genutzten DLT-Verfahren über Methoden mit Verzeichnungskorrektur bis zu Bündelausgleichsverfahren. Im Anschluss werden die für die verwendeten Kameras geeigneten Methoden auf Basis funktionaler Hardwaretests ausgewählt und weitere für das Bewegungserfassungssystem notwendige Softwarekomponenten diskutiert. Dazu gehören neben der automatisierten Video- und Bildverarbeitung, spezielle Verfahren zur Korrektur von Consumer-Kamera-spezifischen Abweichungen, z.B. die Korrektur von Rolling-Shutter-Verzerrungen. Im zweiten Teil der Arbeit richtet sich der Fokus auf die Simulation der Effekte von Parameterungenauigkeiten auf die Systemgenauigkeit sowie auf die Validierung und den Test des implementierten Systems. Dabei konnte die Rekonstruktionsgenauigkeit von 11.86mm bei einer Referenzrahmenkalibration durch den Einsatz der Kalibrationsmethode mit Bündelausgleichsverfahren von Svoboda u. a. (2005) auf maximal 4.126mm (M=0.073 mm; SD=1.486 mm) reduziert werden. Diese Methode erlaubt zudem eine einfachere Kalibration größerer Messvolumen ohne aufwändige Referenzrahmen und ist daher ideal für den sportwissenschaftlichen Einsatz geeignet. Ein weiteres Ergebnis der Arbeit ist die theoretische Ableitung der Fehlerfortpflanzung für die Prozessschritte der Bewegungserfassung. In Kombination mit der entwickelten Simulationsumgebung wird damit die Grundlage für eine Prädiktion der erreichbaren Messunsicherheit bereits vor der eigentlichen Messung gelegt.

Nonrigid Motion Compensation of Free Breathing Acquired Myocardial Perfusion Data

In this work, we present a novel method to compensate the movement in images acquired during free breathing using first-pass gadolinium enhanced, myocardial perfusion magnetic resonance imaging (MRI). First, we use independent component analysis (ICA) to identify the optimal number of independent components (ICs) that separate the breathing motion from the intensity change induced by the contrast agent. Then, synthetic images are created by recombining the ICs, but other then in previously published work (Milles et al. 2008), we omit the component related to motion, and therefore, the resulting reference image series is free of motion. Motion compensation is then achieved by using a multi-pass non-rigid image registration scheme. We tested our method on 15 distinct image series (5 patients) consisting of 58 images each and we validated our method by comparing manually tracked intensity profiles of the myocardial sections to automatically generated ones before and after registration. The average correlation to the manually obtained curves before registration 0:89 0:11 was increased to 0:98 0:02