Experimental study of temperatures in characteristic sections of the working zone of a closed two-phase thermosyphon under the condition of a heat removal by external periphery

We present the results of the experimental study of temperature fields in a closed two-phase thermosyphon. Operational modes of a thermosyphon with different heat supply conditions are studied experimentally using setup consisting of the copper case, systems of heat supply and removal in evaporation and condensation zones, and temperature recording facilities. The height of the heat exchanger is 161 mm, thickness of the side walls and bottom wall are 1.5 mm and 2 mm, respectively, inner diameter is 39 mm. Heat is supplied to the bottom wall by heating element. The heat carrier is distilled water. We obtained thermograms when heat fluxes to the bottom wall of the thermosyphon are 695 - 2136 W/m{2}

Fortschritte in der Videokodierung mittels Hintergrundsprites - Ein Beitrag zur universellen Verwendbarkeit

Diese Dissertation präsentiert neuartige Ansätze und erweiterte Techniken zur Kodierung digitaler Videos mittels Hintergrundsprites bzw. Hintergrundmosaiken. Sprites stellen visuelle Zusammenfassungen des starren Hintergrunds einer aufgenommenen Szene dar. Sie werden in übergroßen Bildern repräsentiert, welche möglichst keine Vordergrundobjekte enthalten. Diese Art der Redundanzreduktion ist ideal für die Videokodierung, da die gesamte Hintergrundinformation in dem Sprite und einigen wenigen Projektionsparametern enthalten ist. Die Erstellung von Hintergundsprites ist allerdings nur für ganz bestimmte Szenen möglich. Da eine erfolgreiche Kodierstrategie vor allem universell, also für jede Art von Videomaterial einsetzbar sein soll, liegt das Hauptaugenmerk dieser Arbeit auf der Entwicklung von Techniken, welche die Möglichkeiten der spritebasierten Videokodierung erweitern. Erste Ansätze, wie sie schon im MPEG-4 Standard festgelegt wurden, finden aufgrund des Mangels an Universalität in der Praxis leider keine Anwendung. Hierfür werden in dieser Arbeit vor allem Verfahren zur multiplen Spritegenerierung und zur automatischen Segmentierung der sich unabhängig bewegenden Fordergrundobjekte vorgestellt. Während multiple Sprites die Erzeugung degenerierter Sprites verhindern und gleichzeitig den Einfluss geometrischer Verzerrungen bei der Projektion minimieren, ermöglicht die Segmentierung eine automatische Trennung von Hintergrund und Vordergrund und bildet somit eine wesentliche Grundlage zur objektbasierten Videokodierung. Die hier vorgestellten Segmentierungstechniken bauen direkt auf bereits erstellten Hintergrundsprites auf und lassen sich daher sehr gut den Gesamtprozess der Kodierung integrieren. Einen weiteren wichtigen Aspekt dieser Dissertation bildet die qualitative Verbesserung der Hintergrundmodellierung mittels Sprites. Da moderne hybride Kodierverfahren sehr effizient sind und qualitativ hochwertige Ergebnisse liefern, muss die Qualität herkömmlicher spritebasierter Prädiktion des Hintergrunds erheblich verbessert werden. Hierfür werden exakte Bildregistrierungs- und Spritegenerierungsverfahren vorgestellt. Dabei wird vor allem die Möglichkeit der Superresolution ausgenutzt. Da die Diskretisierung der visuellen Information bei der Videoaufnahme mehrfach und mit verschiedenen Abtastmustern erfolgt, können mehrere Bilder einer Szene zur Erhöhung der Auflösung des Sprites genutzt werden. Dies wirkt sich positiv sowohl auf die Kodierqualität als auch auf das Verhältnis von Qualität zu Übertragungsrate aus. Letztendlich werden zwei Techniken zur spritebasierten Videokodierung vorgestellt, welche die präsentierten Ansätze zur verbesserten Universalität und Qualität der Hintergrundmosaike verwenden. Der erreichte Kodiergewinn gegenüber neuesten Standardkodierverfahren bestätigt dabei die Nützlichkeit dieser Methoden. Eine vollständig universelle Kodierung jeglichen Videomaterials kann damit noch nicht erreicht werden, ein möglichst vollständiges System hierzu wird aber bereits skizziert. Diese Arbeit liefert somit einen Beitrag zu einem allmählichen Paradigmenwechsel in der Videokodierung, bei dem in zunehmendem Maße Werkzeuge der Computer Vision und der Computergrafik benutzt werden, um verschiedene Teile eine Videoszene unterschiedlich zu kodieren.This dissertation presents new approaches end extended techniques for the coding of digital video using background sprites, also called background mosaics. Sprites form a visual summarization of the rigid background of a captured scene shot. They are represented in oversized images, which preferably do not contain any foreground objects. This type of redundancy reduction is an ideal tool for video coding since the complete background information can be stored in the sprite image and some additional projection parameters. However, the generation of sprites is only possible for certain scenes. Since a successful coding strategy has to be universally applicable, the development of techniques for facilitating a broader use of sprite-based video coding represents the main focus of this thesis. Early approaches, as the one adopted in the MPEG-4 standard, have not been utilized due to the lack of universality and usability. For this purpose, we present techniques for the generation of multiple sprites and provide automatic segmentation approaches for the independently moving foreground objects. While multiple sprites prevent the construction of degenerated sprites and simultaneously minimize the impact of geometrical distortions, the segmentation enables the automatic discrimination in foreground and background objects. Thus, it is a fundamental tool for object-based video coding. The presented segmentation techniques are built upon the background sprites and thus, are easy to integrate into the overall coding process. The improvement of the background modeling using sprites marks another important aspect of this dissertation. Since state-of-the-art hybrid coding strategies work very efficient and yield high quality results, the prediction quality of the background using sprites has to be improved remarkably. In order to achieve this goal, we present novel image registration and sprite generation algorithms. Especially the potential of super-resolution processing will be exploited. Due to the capturing process, we obtain several differently sampled versions of the same image content. This fact can be used for the construction of background sprites of enhanced resolution, which has a positive influence on the resulting coding quality as well as on the rate-distortion results. Eventually, two techniques for sprite-based video coding are presented. Both approaches utilize above mentioned tools for improving quality and universality of the sprites. The coding gain over latest standards proves their usefulness. A complete coding system for the processing of any video content is still not achieved, but an outlook of its possible architecture is drafted. Thus, this thesis contributes to a gradual change of the video coding paradigm, where additional instruments from computer vision and computer graphics are utilized to unequally encode independent parts of a video scene

Object-Based Multiple Sprite Coding of Unsegmented Videos using H.264/AVC

In spite of recent progress in the development of hybrid block-based video codecs, it has been shown that for low-bitrate scenarios there is still coding gain applying object-based techniques. We present a sprite-based codec, based on latest H.264 features using an inbuilt segmentation approach for scenes recorded by a rotating camera. The segmentation itself is built up on reliable background estima-tion from the sprite and short-term image registration. Moreover, we generate multiple sprites based on physical camera parameter esti-mation that overcome three of the main drawbacks of sprite coding techniques. First, the coding cost for the sprite image is minimized. Second, multiple sprites allow temporal background refresh and fi-nally, registration error accumulation is kept very small. Experimen-tal results show that this coding approach significantly outperforms latest H.264 extensions applying hierarchical B pictures. Index Terms — Object-based video coding, sprite coding, mul-tiple sprites, H.264/AVC 1

WINDOWED IMAGE REGISTRATION FOR ROBUST MOSAICING OF SCENES WITH LARGE BACKGROUND OCCLUSIONS

We propose an enhanced window-based approach to localimage registration for robustvideo mosaicing in scenes with arbitrarily moving foreground objects. Unlike other approaches, we estimate accurately the image transformation without any pre-segmentation even iflarge background regions are occluded. We apply awindowed hierarchical frame-to-frame registration based on image pyramid decomposition. In the lowest resolution level phase correlation for initial parameter estimation is used while in the next levels robust Newton-based energy minimization of the compensated image mean-squared error is conducted. To overcome the degradation error caused by spatial image interpolation due to the warping process, i.e. aliasing effects from under-sampling, final pixel values are assigned in an up-sampled image domain using a Daubechies bi-orthogonal synthesis filter. Experimental results show the excellent performance of the method compared to recently published methods. The image registration is sufficiently accurate to allow open-loop parameter accumulation for long-term motion estimation

Robust Concealment for Erroneous Block Bursts in Stereoscopic Images

With the increasing number of image communication applications especially in the low complexity domain, error concealment has become a very important field of research. Since many compression standards for images and videos are block-based a lot of methods were applied to conceal block losses in monocular images. The fast progress of capture, representation and display technologies for 3D image data advances the efforts on 3D concealment strategies. Because of their psycho-visual characteristics, stereoscopic images have to fulfill a very high quality demand. We propose an algorithm that makes use of the redundancies between two views of a stereo image pair. In many cases erroneous block bursts occur and can be highly disturbing, thus we will mainly concentrate on these errors. In addition, we focused on the quality assessment of several error concealment strategies. Beside the objective evaluation measures, we carried out a subjective quality test following the DSCQS methodology as proposed by MPEG. The results of this test demonstrate the efficiency of our approach

A Hybrid Approach For Error Concealment In Stereoscopic Images

Error concealment for stereoscopic images receives little attention in research of image processing. While many methods have been proposed for monocular images, this paper considers a concealment strategy for block loss in stereoscopic image pairs, utilizing the information of the associated image to fulfill the higher quality demand. We present a hybrid approach, combining a 2D projective transformation and a monoscopic error concealment technique. Pixel values from the associated stereo image are warped to their corresponding positions in the lost block. To reduce discontinuities at the block borders, a monoscopic error concealment algorithm with low-pass properties is integrated. The stereoscopic depth perception is much less affected in our approach than using only monoscopic error concealment techniques

A Gradient Based Approach for Stereoscopic Error Concealment

Error concealment is an important field of research in image processing. Many methods were applied to conceal block losses in monocular images. In this paper we present a concealment strategy for block loss in stereoscopic image pairs. Unlike the error concealment techniques used for monocular images, the information of the associated image is utilized , i.e., by means of a projective transformation model, pixel values from the associated stereo image are warped to their corresponding positions in the lost block. The stereoscopic depth perception is much less affected in our approach than using monoscopic error concealment techniques

Motion-based Object Segmentation using Sprites and Anisotropic Diffusion

Many algorithms have been developed to recognize re-gions, edges, color, and objects in images and videos. For applications like surveillance or object-based video coding, it is important to segment the foreground objects from the background. The task is very challenging in the case of a moving camera. We present a foreground segmentation ap-proach that is designed for sprite coding as well as other applications, e.g. video surveillance. Accurate frame-to-frame image registration and sprite generation build the pre-processing step. The segmentation algorithm operates on error images, which are produced by the image registra-tion and subtraction from reconstructed background frames. It is processed in several steps including low-pass filtering using anisotropic diffusion. Experiments show excellent re-sults with single- and multi-view test sequences. 1

Optimal Multiple Sprite Generation based on Physical Camera Parameter Estimation

We present a robust and computational low complex method to estimate the physical camera parameters, intrinsic and extrinsic, for scene shots captured by cameras applying pan, tilt, rotation, and zoom. These parameters are then used to split a sequence of frames into several subsequences in an optimal way to generate multiple sprites. Hereby, optimal means a minimal usage of memory while keeping or even improving the reconstruction quality of the scene background. Since wide angles between two frames of a scene shot cause geometrical distortions using a perspective mapping it is necessary to part the shot into several subsequences. In our approach it is not mandatory that all frames of a subsequence are adjacent frames in the original scene. Furthermore the angle-based classification allows frame reordering and makes our approach very powerful