Three Dimensional Television (3DTV) and Free Viewpoint Television (FTV) are emerging multimedia applications, which promise to offer a new Quality of Experience (QoE) dimension. In order for such applications to offer an immersive experience for users a large number of viewpoints need to be transmitted, to a point where the high bandwidth utilisation becomes a major concern. One approach to this problem is the utilisation of the so called “depth maps” in Depth Image Based Rendering (DIBR) techniques, where different views, can be reconstructed (rendered) at the receiver side when required, with a fraction of the bandwidth. Therefore the quality and accuracy of the information present in depth maps and its ability to reconstruct the required views has become the subject of much greater scrutiny in multimedia research. Several challenges arise when assessing the quality of depth maps, such as the lack of a proper reference for comparing the available depth maps, especially when it comes to live High Definition (HD) content. The first contribution of this thesis focuses on developing a novel subjective assessment approach, which addresses the presence of disocclusions in rendered views. The goal of this assessment approach is to enable the subjective evaluation of rendered views, to provide results that are more representative of the quality of the depth map utilised in the rendering process. The adopted approach performance has been evaluated through correlating the obtained subjective results with well-established objective metric measurements, such as PSNR, PSPNR, SSIM and VQM. The second contribution of this thesis is concerned with establishing a test data set, which includes different colour sequences together with various depth estimation algorithms and different depth post processing techniques. State of the art depth estimation algorithms were examined such as RSGM, DERS and HRM, in order to obtain a wide range of depth map qualities. The depth map data set is utilised in the DIBR process to generate rendered views, which are in turn subjectively assessed utilising the approach developed in contribution one of this thesis. The assessment is carried out in both a 2D and 3D setup and statistical analysis is utilised to establish observations and conclusions over the depth map performance. The third and final contribution of this thesis is related to a non-reference evaluation approach in assessing the quality of the depth maps utilised. This approach exploits the edges present in the available depth maps and compares that to the edges in the corresponding colour views. Edge pixels in depth maps are then classified into correct and error edge pixels. The obtained results are then correlated with the subjective results obtained in the second contribution. The result analysis of this non-reference model provides clear indications of depth map performance and its dependency on the associated colour sequence selection. The high correlation values with the subjective results were in the range of 75-81%. These correlation values are of more significance when compared to best performing quality metrics (e.g. VQM obtained correlation values of 59%) under the researched scenarios.

Humans have an innate ability to communicate visually; the earliest forms of communication were cave drawings, and children can communicate visual descriptions of scenes through drawings well before they can write. Drawings and sketches offer an intuitive and efficient means for communicating visual concepts. Today, society faces a deluge of digital visual content driven by a surge in the generation of video on social media and the online availability of video archives. Mobile devices are emerging as the dominant platform for consuming this content, with Cisco predicting that by 2018 over 80% of mobile traffic will be video. Sketch offers a familiar and expressive modality for interacting with video on the touch-screens commonly present on such devices. This thesis contributes several new algorithms for searching and manipulating video using free-hand sketches. We propose the Visual Narrative (VN); a storyboarded sequence of one or more actions in the form of sketch that collectively describe an event. We show that VNs can be used to both efficiently search video repositories, and to synthesise video clips. First, we describe a sketch based video retrieval (SBVR) system that fuses multiple modalities (shape, colour, semantics, and motion) in order to find relevant video clips. An efficient multi-modal video descriptor is proposed enabling the search of hundreds of videos in milliseconds. This contrasts with prior SBVR that lacks an efficient index representation, and take minutes or hours to search similar datasets. This contribution not only makes SBVR practical at interactive speeds, but also enables user-refinement of results through relevance feedback to resolve sketch ambiguity, including the relative priority of the different VN modalities. Second, we present the first algorithm for sketch based pose retrieval. A pictographic representation (stick-men) is used to specify a desired human pose within the VN, and similar poses found within a video dataset. We use archival dance performance footage from the UK National Resource Centre for Dance (UK-NRCD), containing diverse examples of human pose. We investigate appropriate descriptors for sketch and video, and propose a novel manifold learning technique for mapping between the two descriptor spaces and so performing sketched pose retrieval. We show that domain adaptation can be applied to boost the performance of this system through a novel piece-wise feature-space warping technique. Third, we present a graph representation for VNs comprising multiple actions. We focus on the extension of our pose retrieval system to a sequence of poses interspersed with actions (e.g. jump, twirl). We show that our graph representation can be used for multiple applications: 1) to retrieve sequences of video comprising multiple actions; 2) to navigate in pictorial form, the retrieved video sequences; 3) to synthesise new video sequences by retrieving and concatenating video fragments from archival footage.

If a digital TV signal is successfully received and decoded it can guarantee a set picture quality. Clear operational power thresholds due to the hard failure of digital TV can be set, however when a digital system is operating far in excess of the operational threshold, there is no discernible advantage to either the user or broadcaster. This is effectively a waste of broadcast power; if the system could be adaptively tuned to operate at just above the threshold then the energy efficiency of the overall system would be improved. If the broadcaster had access to accurate. Channel State Information (CSI), then the entire broadcast system could be made adaptive. CSI would come via feedback from television equipment, creating a distributed monitoring network that operates over the internet. In this way, data relating to the quality of a users' channel could be fed back to the broadcaster for use in adaptive algorithms and applied to beamforming techniques to ensure the most energy efficient level of coverage is achieved. To explore the feasibility of an adaptive TV broadcast system, the problem was tackled in three ways in this thesis; computer simulations of an overall system, hardware in the loop analysis of an adaptive system in lab conditions and the use of a professional digital TV planning tool to explore the advantages of static beamforming in the UK network. The work undertaken as part of this thesis built up and analysed an adaptive digital TV broadcast system. The effects of such a system on the UK Digital. Terrestrial Television (DTT) network was studied and the advantages became clear, with potential power savings of up to 2 dB being realised. This equates to an approximate electricity reduction of between 56 million and 98 million kWh per year, which is an annual saving of between £6 million and £11 million and a reduction in carbon emissions by between 25 million and 45 million kg C02e over the same period. This therefore shows a major improvement of the energy efficiency of the UK DTT network.

Steadily-increasing user demand for a wide range of high-quality video services delivered via satellite has driven broadcasters to move into the Ka-band and higher frequency spectrum in order to accommodate the necessary data rates. However, a major issue at these frequencies is the effect of severe rain-induced fading on link reliability, which requires that the system must be designed to implement mitigation techniques in order to achieve an acceptable quality-of-service. These techniques generally involve the use of adaptive modulation and data rates, together with various forms of diversity, switching or combining. In this thesis, we analyse and quantify the benefits of adding Time Diversity (TD) and Maximal Ratio Combining (MRC) to the widely-used DVB-S2 standard. Our results, which are based on i) 3 years of satellite beacon propagation measurements from 2 UK sites; ii) high-fidelity computer simulations; and iii) our new TD / MRC technology, indicate that substantial improvements in data throughput and significant reductions in outage time are readily achievable. Accurate knowledge of the statistical distribution of rain attenuation is necessary for the proper design of a Fade Mitigation Technique (FMT) to operate with the required level of service availability. Therefore, since July 2010, the University of South Wales and the Science and Technology Facilities Council have undertaken a programme of simultaneous satellite beacon measurements at the University campus in Pontypridd, Wales, and at the STFC Chilbolton Observatory, in Southern England, respectively. Transmissions from the Eutelsat Hotbird l3A (previously Hotbird 6) satellite at 19.7 GHz were recorded, together with meteorological measurements, at both sites. These data enabled reliable estimation of the instantaneous propagation conditions and carrier-to-noise ratio on the Ku-band beacon downlinks. Using standard ITU-R recommendations, the resulting data-set of measured 19.7 GHz attenuations was also frequency- scaled to yield a predicted data-set of 29.5 GHz attenuations. Thereby, the performance of an operationally-representative, hypothetical DVB-S2 communications link, with uplink at 30 GHz (from Chilbolton to the satellite), and downlink at 20 GHz (from the satellite to Pontypridd), was analysed based on l-year's data. The DVB-S2 transmission and reception signal processing architecture has been faithfully implemented in the MATLAB simulation environment with reference to the appropriate technical standards documents. Extensive testing has been conducted to verify that the bit error rate performance of the MATLAB simulation closely matches that defined in the DVB-S2 standard for all combinations of modulation schemes and coding rates. Inputs to the simulator comprise a test data stream (which can be a real HDTV signal), together with the uplink and downlink attenuation time- series data for the fading event being studied. Outputs consist of the bit error rate statistics and modulation scheme / coding rate configuration as a function of time, the total data throughput over the event duration, and the demodulated baseband signal. A novel feature of this work is the extension of the existing DVB-S2 standard to include TD and MRC. During periods of fading, TD is enabled, such that the transmitted data is duplicated into 2 parallel streams with a suitably-chosen time offset between them. In the receiver, MRC is employed in order to obtain a greater SNR improvement than could be achieved by the more traditional switched-combining method. We have designated this extended version of the DVB-S2 standard, incorporating the twin techniques of TO and MRC, as DVB-S2-TD. It provides the potential to continue delivering services at SNRs significantly below the currently acceptable threshold for DVB-S2, such as would be experienced under the propagation impairments associated with severe weather conditions. In this thesis, we describe the experimental systems used to collect the satellite beacon and meteorological measurements. The implementation of the MATLAB simulator for DVB-S2 is then discussed, together with the enhancements for TD and MRC. Finally, we compare the performance of DVB-S2 and DVB-S2-TD, so as to demonstrate the operational benefits of our new techniques.

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Consumption and production of video signals drastically changed in recent years. Due to the advances in digital consumer technology and the growing availability of fast and reliable internet connections, an increasing amount of digital video sequences are being produced, stored and shared every day in different parts of the world. Video signals are inherently larger in size than other types of multimedia signals. For this reason in order to allow transmission and storage of such data, more efficient compression technology is needed. In this thesis novel methods for enhancing the efficiency of current and next generation video codecs are investigated. Several aspects of interest to video coding technology are taken into account, from computational complexity and compliance to standardisation efforts, to compression efficiency and quality of the decoded signals. Compression can be achieved exploiting redundancies by computing a prediction of a part of the signal using previously encoded portions of the signal. Novel prediction methods are proposed in this thesis based on analytical or statistical models with the aim of providing a solid theoretical basis to support the algorithmic implementation. It is shown in the thesis that appropriately defined synthetic content can be introduced in the signal to compensate for the lack of certain characteristics in the original content. Some of the methods proposed in this thesis aim to target a broader set of use cases than those typically addressed by conventional video coding methods, such as ultra high definition content or coding under high quality conditions.

In this thesis, I seek to understand what shaped the development of television, tracing the technology back to its earliest roots. In existing literature, the history of television in its formative years (before World War II), has largely been presented in technologically deterministic terms, culminating in the ‘goal’ of adding ‘sight to sound’ – producing a wireless set with pictures. Most of the existing literature focuses on ‘hero’ figures such as British inventor John Logie Baird and his electro-mechanical television systems, or on corporate narratives such as that of RCA in the United States in developing all-electronic television. In contrast to such an approach, I will concentrate on the transnational networks linking individuals and companies, and on the common external factors affecting all of them. Some networks could operate simultaneously as rivals and collaborators, as was the case with companies such as Marconi-EMI in Britain and RCA in the United States. Senior managers and researchers such as Isaac Shoenberg at Marconi-EMI and Vladimir Zworykin at RCA played significant roles, but so too did relatively obscure figures such as Russian scientist Boris Rosing and British engineer Alan A Campbell Swinton. I will draw on newly available sources from Russia and the USSR, on over-looked sources in Britain and the United States, and on replicative technology to re-examine the story. The new material, coupled with the transnational networks approach, enables fresh insights to be gained on issues of simultaneity of invention and on contingency in the development and initial deployments of the technology. By using these fresh primary sources, and by re-interpreting some aspects of the numerous existing secondary sources, I will show that the ‘wireless with pictures’ model was not inevitable, that electro-mechanical television need not have been a technical cul-de-sac, and that in Britain at least, it was the political desire to maintain and extend the monopoly of the BBC, which effectively funnelled the technology into the model so familiar to us today.

Η διπλωματική εργασία έχει σαν σκοπό την ανάπτυξη ενός μοντέλου μέτρησης των παραμέτρων που επηρεάζουν την ποιότητα υπηρεσίας ενός βίντεο IPTV. Αναφέρονται επιγραμματικά όλες οι υπάρχουσες τεχνολογίες παράδοσης ψηφιακής τηλεόρασης και αναλύονται όλες οι τεχνολογίες και η αρχιτεκτονική της IPTV. Επίσης υπάρχει περιγραφή και ανάλυση όλων των μηχανισμών που πρέπει να χρησιμοποιηθούν ούτως ώστε να μειωθεί όσο το δυνατόν περισσότερο η επίδραση των παραμέτρων (απώλεια πακέτων, καθυστέρηση, jitter, εύρος ζώνης) στην ποιότητα υπηρεσίας της IPTV. Τέλος υπάρχει σύγκριση της IPTV με όλες τις υπόλοιπες μεθόδους παράδοσης ψηφιακής τηλεόρασης καθώς και με το Internet TV. / The aim of this paper is to create a model that measures the parameters of quality of service in IPTV. All the existing technologies that we use today for the delivery of digital television are succinctly reported and analyzed as well as the technologies and architecture of IPTV. There is also the description and analysis of all the mechanisms that the providers should use to decrease as much as possible the effect of the above parameters (packet loss, delay, jitter, bandwith) in the quality of service of IPTV. Finally there is a comparison of IPTV with all the technologies that we use for the delivery of digital television as well as with the Internet TV.

Η διπλωματική εργασία μελετά την παροχή υπηρεσιών ψηφιακής τηλεόρασης (DVB) από πλατφόρμες μεγάλου υψομέτρου (High Altitude Platforms-HAPs). Στο πρώτο κεφάλαιο γίνεται μια εισαγωγή στις δορυφορικές επικοινωνίες κομμάτι των οποίων θεωρούνται και οι στρατοσφαιρικές πλατφόρμες. Στο δεύτερο κεφάλαιο αναλύονται θέματα των πλατφορμών αυτών, όπως τα πλεονεκτήματα και μειονεκτήματα τους σε σύγκριση με άλλα δορυφορικά και επίγεια συστήματα, ο σχεδιασμός του καναλιού, δίκτυα αποτελούμενα από στρατοσφαιρικές πλατφόρμες και οι τομείς στους οποίους αυτά βρίσκουν εφαρμογή. Στο τρίτο κεφάλαιο παρουσιάζεται το πρότυπο δορυφορικής μετάδοσης ψηφιακού βίντεο DVB-S, τα σχήματα διαμόρφωσης και κωδικοποίησης που χρησιμοποιεί, οι απαιτήσεις του αλλά και το πρόσφατο DVB-S2. Στο τελευταίο κεφάλαιο παρατίθενται οι εξομοιώσεις που πραγματοποιήθηκαν στα πλαίσια της εργασίας καθώς και τα αποτελέσματα που λήφθηκαν για διάφορα είδη διαμόρφωσης και για μεταβολή των παραμέτρων του ενδιάμεσου καναλιού. Η εργασία καταλήγει με μια σύντομη σύγκριση του στρατοσφαιρικού συστήματος με ένα επίγειο σύστημα μετάδοσης ψηφιακής τηλεόρασης. / -