published_or_final_version / abstract / toc / Electrical and Electronic Engineering / Master / Master of Philosophy

With advances in imaging and communication systems, there is increased use of multi-dimensional images. Examples include multi-view image/video, hyperspectral image/video and dynamic volume imaging in CT/MRI/Ultrasound. These datasets consume even larger amounts of resources for transmission or storage compared to 2-D images. Hence, it is vital to have efficient compression methods for multi-dimensional images. In this dissertation, first, a JPEG2000 Part-2 compliant scheme is proposed for compressing multi-dimensional datasets for any dimension N>=3. Secondly, a novel view-compensated compression method is investigated for remote visualization of volumetric data. Experimental results indicate superior compression performance compared to state-of-the-art compression standards. Thirdly, a new scalable low complexity coder is designed that sacrifices some compression efficiency to get substantial gain in throughput. Potential use of the scalable low complexity coder is illustrated for two applications: Airborne video transmission and remote volume visualization.

Three end-member clinopyroxenes from the NaM13+Si2O6 series (M1 = Al, Fe and Ga) have been examined by single-crystal X-ray diffraction at pressures up to 11 GPa. NaGaSi2O6 was also examined with Raman spectroscopy to 16.5 GPa. NaAlSi2O6 (jadeite) and NaFeSi2O6 (aegirine) are naturally occurring minerals. NaGaSi2O6 is synthetic. Various characteristics of each of the three clinopyroxenes as a function of pressure are reported, including bulk moduli (K0), unit cell volumes, atomic positions, and bond lengths.The compressibilities of a selection of clino- and orthopyroxenes from the literature were examined and considered in terms of M2-O3 bonding and unit cell volumes. As predicted by previous workers, pyroxene compressibilities generally correlate with unit cell volumes at ambient conditions. Compressibilities are also found, however, to be significantly affected by the relationship of M2-O3 bonds with the sense of rotation of silica tetrahedra upon compression. Two such relationships are observed: sympathetic, where the corner of the SiO4 tetrahedron tilts toward M2, and antipathetic, where the corner of the tetrahedron tilts away from M2. All interatomic separations in pyroxenes decrease with pressure, but sympathetic-type separations decrease more than expected based on isotropic scaling of the unit cell. Pyroxene structures may have one of several M2-O3 bond configurations: none, one, two or four bonds, and none, only sympathetic, only antipathetic, or a mixture of both types of bonds. Structures with antipathetic bonds are significantly stiffer than structures without, all else constant. The sympathetic/antipathetic bond hypothesis represents a new, previously unrecognized, first-order control on pyroxene compressibility.M1 size controls ambient unit cell volumes of clinopyroxenes. However, M1 size does not correlate well with pyroxene bulk moduli. Applying the idea of sympathetic and antipathetic M2-O3 bonding, much of the dispersion in a plot of M1 cation size versus bulk modulus can be explained. The three NaM13+Si2O6 clinopyroxenes examined in this study exhibit very similar behavior under compression. All show signs of approaching a C2/c -> C2/c phase transition at ~20 GPa. All exhibit unit strain ellipsoids with similar orientations and dimensions. All have identical bond topologies and bulk moduli that correlate with their ambient unit cell volumes.

Uncompressed multimedia data requires considerable storage capacity and transmission bandwidth. Despite rapid progress in mass-storage density, processor speeds, and digital communication system performance, demand for data storage capacity and data-transmission bandwidth continues to outstrip the capabilities of available technologies. The recent growth of data intensive multimedia-based web applications even more sustained the need for more efficient ways to encode such data. There are two types of image compression schemes – lossless and lossy algorithms. In lossless compression schemes, the reconstructed image, after compression, is numerically identical to the original image. However lossless compression can only achieve a modest amount of compression. An image reconstructed following lossy compression contains degradation relative to the original. Often this is because the compression scheme completely discards redundant information. However, lossy schemes are capable of achieving much higher compression. The aim of this research is to create an efficient lossy image compression algorithm, using heuristic data clusterization methods; perform experiments of the new algorithm, measure its performance, analyze advantages and disadvantages of the proposed method, propose possible improvements and compare it with other popular algorithms. In this paper is presented new algorithm for image compression, which uses data base of popular image fragments. Proposed algorithm is... [to full text]

One of the images compression methods – fractal image compression is analyzed in the work. After work carried out, it is possible to state, that selecting parameters of method of fractal compression depends on user’s demands.

Les entrepôts de données jouent un rôle important dans la collecte et l'archivage d'une grande masse d'informations. Ces dernières sont utilisées dans la gestion et la prise des décisions pour des affaires stratégiques de l'entreprise. Cependant, l'exécution des requêtes complexes dans une grande masse d'information dégrade les performances du système d'entrepôt de données, dont la vitesse d'exécution des requêtes. Une des techniques les plus répandues pour remédier au problème précédent est de mettre en place un algorithme de compression de données. En effet, la compression de données permet d'une part de réduire le volume de données d'une table et d'autre part de charger et de traiter beaucoup des données en mémoire centrale et évite l'accès fréquent au disque de l'ordinateur. Aujourd'hui, il existe plusieurs systèmes de gestion de base de données qui intègrent différents algorithmes de compression de données. La plupart de ces algorithmes convergent vers une technique commune basée sur l'utilisation d'un dictionnaire de données. Ce dernier permet d'enregistrer une valeur unique correspondante aux données répétitives trouvées dans la table de données. Notre recherche dans ce mémoire vise, premièrement, à exploiter les algorithmes de compressions en particulier l'algorithme de compression de base de données Oracle; deuxièmement, à proposer un nouveau prototype de compression de données inspiré de l'approche Oracle. Ce prototype introduit un nouveau concept d'un dictionnaire hiérarchique. Ce dernier est défini par une structure hiérarchique contenant un super dictionnaire de données relié à plusieurs dictionnaires de données. Le super dictionnaire a pour rôle d'enregistrer toutes les valeurs communes entre les dictionnaires. La mise en œuvre de ce nouveau prototype a pour but de développer les techniques de compression de données et d'améliorer les performances de l'entrepôt de données. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Entrepôt de données (ACM 98, H.2.7), Compression (ACM 98, E.4), Dictionnaires (ACM 98, H.3.1), Performances (ACM 98, K.6.2).

Current hybrid coders such as H.261/263/264 or MPEG-l/-2 cannot always offer high quality-to-compression ratios for video transfer over the (low-bandwidth) wireless channels typical of handheld devices (such as smartphones and PDAs). Often these devices are utilised in videophone and teleconferencing scenarios, where the subjects of inte:est in the scene are peoples faces. In these cases, an alternative coding scheme known as Model-Based Video Coding (MBVC) can be employed. MBVC systems for face scenes utilise geometrically and photorealistically accurate computer graphic models to represent head !md shoulder views of people in a scene. High compression ratios are achieved at the encoder by extracting and transmitting only the parameters which represent the explicit shape and motion changes occurring on the face in the scene. With some a priori knowledge (such as the MPEG-4 standard for facial animation parameters), the transmitted parameters can be used at the decoder to accurately animate the graphical model and a synthesised version of the scene (originally appearing at the encoder) can be output. Primary components for facial re-animation at the decoder are a set of local and global motion parameters extracted from the video sequence appearing at the encoder. Local motion describes the changes in facial expression occurring on the face. Global motion describes the three-dimensional motion· of the entire head as a rigid object. Extraction of this three-dimensional global motion is often called head tracking. This thesis focuses on the tracking of rigid head pose in a monocular video sequence. The system framework utilises the recursive Structure from Motion (SfM) method of Azarbayejani and Pentland. Integral to the SfM solution are a large number of manually selected two-dimensional feature points, which are tracked throughout the sequence using an efficient image registration technique. The trajectories of the feature points are simultaneously processed by an extended Kalman filter (EKF) to stably recover camera geometry and the rigid three-dimensional structure and pose of the head. To improve estimation accuracy and stability, adaptive estimation is harnessed within the Kalman filter by dynamically varying the noise associated with each of the feature measurements. A closed loop approach is used to constrain feature tracking in each frame. The Kalman filter's estimate of motion and structure of the face are used to predict the trajectory of the features, thereby constraining the search space for the next frame in the video sequence. Further robustness in feature tracking is achieved through the integration of a linear appearance basis to accommodate variations in illumination or changes in aspect on the face. Synthetic experiments are performed for both the SfM and the feature tracking algorithm. The accuracy of the SfM solution is evaluated against synthetic ground truth. Further experimentation demonstrates the stability of the framework to significant noise corruption on arriving measurement data. The accuracy of obtained pixel measurements in the feature tracking algorithm is also evaluated against known ground truth. Additional experiments confirm feature tracking stability despite significant changes in target appearance. Experiments with real video sequences illustrate robustness of the complete head tracker to partial occlusions on the face. The SfM solution (including two-dimensional tracking) runs near real time at 12 Hz. The limits of Pitch, Yaw and Roll (rotational) recovery are 45°,45° and 90° respectively. Large translational recovery (especially depth) is also demonstrated. The estimated motion trajectories are validated against (publically available) ground truth motion captured using a commercial magnetic orientation tracking system. Rigid reanimation of an overlayed wire frame face model is further used as a visually subjective analysis technique. These combined results serve to confirm the suitability of the proposed head tracker as the global (rigid) motion estimator in an MBVC system. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2005.

The success of the wavelet transform in the compression of still images has prompted an expanding effort to exercise this transform in the compression of video. Most existing video compression methods incorporate techniques from still image compression, such techniques being abundant, well defined and successful. This dissertation commences with a thorough review and comparison of wavelet still image compression techniques. Thereafter an examination of wavelet video compression techniques is presented. Currently, the most effective video compression system is the DCT based framework, thus a comparison between these and the wavelet techniques is also given. Based on this review, this dissertation then presents a new, low-complexity, wavelet video compression scheme. Noting from a complexity study that the generation of temporally decorrelated, residual frames represents a significant computational burden, this scheme uses the simplest such technique; difference frames. In the case of local motion, these difference frames exhibit strong spatial clustering of significant coefficients. A simple spatial syntax is created by splitting the difference frame into tiles. Advantage of the spatial clustering may then be taken by adaptive bit allocation between the tiles. This is the central idea of the method. In order to minimize the total distortion of the frame, the scheme uses the new p-domain rate-distortion estimation scheme with global numerical optimization to predict the optimal distribution of bits between tiles. Thereafter each tile is independently wavelet transformed and compressed using the SPIHT technique. Throughout the design process computational efficiency was the design imperative, thus leading to a real-time, software only, video compression scheme. The scheme is finally compared to both the current video compression standards and the leading wavelet schemes from the literature in terms of computational complexity visual quality. It is found that for local motion scenes the proposed algorithm executes approximately an order of magnitude faster than these methods, and presents output of similar quality. This algorithm is found to be suitable for implementation in mobile and embedded devices due to its moderate memory and computational requirements. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2003.

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