Three-dimensional Photoacoustic Tomography System Design Analysis and Optimization

Photoacoustic tomography (PAT) is an emerging imaging modality capable of mapping optical absorption in tissues. It is a hybrid technique that combines the high spatial resolution of ultrasound imaging with the high contrast of optical imaging, and has demonstrated much potential in biomedical applications. Conventional PAT systems employ raster scanning to capture a large number of projections, thus improving image reconstruction at the cost of temporal resolution. Arising from the desire for real-time 3D PA imaging, several groups have begun to design PAT systems with staring arrays, where image acquisition is only limited by the repetition rate of the laser. However, there has been little emphasis on staring array design analysis and optimization. We have developed objective figures of merit for PAT system performance and applied these metrics to improve system design. The results suggested that the developed approach could be used to objectively characterize and improve any PAT system design

Modern video codecs

Tato bakalářská práce se zabývá moderními video kodeky a hodnocením jejich výstupní kvality videa. Nejprve jsou vysvětleny principy některých objektivních i subjektivních metod hodnocení. V další části jsou poté představeny nejpoužívanější video kodeky, konkrétně H.264, H.265, VP8, VP9, Dirac~2.2.3, WMV a Sorenson Spark. Výstupem práce je desktopová aplikace VideoCodecs napsaná v jazyce C++, která pro kódování a dekódování používá knihovnu ffmpeg. Součástí aplikace jsou také algoritmy PSNR, SSIM a~M--SVD pro objektivní hodnocení videa, dále pak simulace přenosového kanálu, umožňující zanesení chyb. Pomocí této aplikace bylo provedeno měření na čtyřech testovacích sekvencích v HD rozlišení při různých bitových rychlostech. Ze srovnání jednotlivých kodeků vyplývá, že nejlepším kodekem, s ohledem na kvalitu obrazu, je kodek H.265 před kodekem H.264, VP9 a VP8.This bachelor's thesis focuses on modern video codecs and its output video quality assessment. Firstly, principles of some objective and subjective assessment methods are explained. Afterwards, the most common video codecs are introduced, namely H.264, H.265, VP8, VP9, Dirac~2.2.3, WMV and Sorenson Spark. The outcome of this thesis is a desktop application named VideoCodecs written in C++ language, which uses ffmpeg library for encoding and decoding tasks. As a part of the application, algorithms PSNR, SSIM and M--SVD for objective video quality assessment were implemented. Furthermore, a simulation of transport channel was included, enabling us to bring errors into provided video. Using this application, video quality measurements were carried out, on four test sequences in HD resolution at several bitrates. According to our results, the best video codec regarding the video quality is H.265 before H.264, VP9 and VP8.

3D video transmission over LTE

This thesis presents a research work on quality of experience in 3D video transmission over LTE networks. The objective is to study the state-of-art of LTE and 3D video, described in the scientific literature, and to quantify the user quality of experience (QoE) during a simulated LTE transmission. The work will start by a study of the University of Wien “LTE-A System Simulator” and its capabilities. In addition, different scenarios with various users equipment (UEs) and base stations (eNodeBs) densities will be configured and simulated in order to obtain the frame-by-frame Block Error Rate (BLER) values experienced by different UEs. Once obtained, the Block Error Rate frames will be converted to packet level error traces, which will be used to introduce erasures and corruptions into the packetized 3D video bitstream. The corrupted encoded video stream will be decoded using an error-concealment capable video decoder and the decoded/recovered video quality (QoE) will be estimated based on the Structural Similarity Index of the recovered video. Finally, the QoE results for the different system configurations will allow classifying the severity of the QoE degradations due to transmission losses, through inferring the relationship between those system parameters and the achievable QoE.Esta dissertação apresenta um trabalho de investigação sobre a qualidade de experiência numa transmissão de vídeo 3D sobre redes LTE. O objectivo é estudar o estado-da-arte no que respeita a rede LTE e vídeo 3D, descrito na literatura científica, e obter a qualidade de experiência de usuário (QoE) durante uma simulação de transmissão LTE. O trabalho começará por um estudo do University of Wien “LTE-A System Simulator” e as suas capacidades. Para este efeito, vão ser configurados diferentes cenários com distintas densidades de utilizadores (UEs) e estações base (eNodeBs), com o fim de obter a taxa de erros do bloco (BLER) experimentada por diferentes utilizadores. Depois de obter esta taxa, as tramas da taxa de erros do bloco (BLER) serão convertidas em tramas de nível de erro de pacotes, que vão ser usadas para adicionar corrupções de bit em ficheiros de vídeo 3D. O fluxo de vídeo codificado e corrompido será descodificado usando um descodificador de vídeo e a qualidade do vídeo recuperado vai ser calculada com base no Índice de Similitude Estrutural. Finalmente, os resultados de QoE para as diferentes configurações do sistema permitirão classificar o nível das degradações de QoE devido a perdas de transmissão, por meio de inferir a relação entre os parâmetros do sistema e a QoE obtida.Ingeniería de Telecomunicació

Investigation of Techniques to increase the Field of View of a Staring Transducer Array for Photoacoustic Imaging

Photoacoustic imaging (PAI) is a hybrid imaging modality that takes advantage of both optical and acoustic techniques for biomedical imaging. It is believed that PAI can successfully assess the margins of lumpectomy specimens in the operating room, decreasing the number of surgeries and wait time for patients. However, current PAI systems do not have sufficient field of view (FOV) to accommodate the size of lumpectomy specimens. In this work, transducer directionality and the use of a shaped matching layer were explored as means to increase the FOV of a staring photoacoustic transducer array. The results indicated that applying a convex matching layer to the face of transducers and directing them toward the centre of the array provides optimal sensitivity throughout the imaging volume. By employing these techniques, any PAI system’s effective FOV can be increased without replacing existing transducers. The optimized system can now be investigated for lumpectomy margin assessment

Perceptual Video Quality Assessment and Enhancement

With the rapid development of network visual communication technologies, digital video has become ubiquitous and indispensable in our everyday lives. Video acquisition, communication, and processing systems introduce various types of distortions, which may have major impact on perceived video quality by human observers. Effective and efficient objective video quality assessment (VQA) methods that can predict perceptual video quality are highly desirable in modern visual communication systems for performance evaluation, quality control and resource allocation purposes. Moreover, perceptual VQA measures may also be employed to optimize a wide variety of video processing algorithms and systems for best perceptual quality. This thesis exploits several novel ideas in the areas of video quality assessment and enhancement. Firstly, by considering a video signal as a 3D volume image, we propose a 3D structural similarity (SSIM) based full-reference (FR) VQA approach, which also incorporates local information content and local distortion-based pooling methods. Secondly, a reduced-reference (RR) VQA scheme is developed by tracing the evolvement of local phase structures over time in the complex wavelet domain. Furthermore, we propose a quality-aware video system which combines spatial and temporal quality measures with a robust video watermarking technique, such that RR-VQA can be performed without transmitting RR features via an ancillary lossless channel. Finally, a novel strategy for enhancing video denoising algorithms, namely poly-view fusion, is developed by examining a video sequence as a 3D volume image from multiple (front, side, top) views. This leads to significant and consistent gain in terms of both peak signal-to-noise ratio (PSNR) and SSIM performance, especially at high noise levels

Perceptual Quality-of-Experience of Stereoscopic 3D Images and Videos

With the fast development of 3D acquisition, communication, processing and display technologies, automatic quality assessment of 3D images and videos has become ever important. Nevertheless, recent progress on 3D image quality assessment (IQA) and video quality assessment (VQA) remains limited. The purpose of this research is to investigate various aspects of human visual quality-of-experience (QoE) when viewing stereoscopic 3D images/videos and to develop objective quality assessment models that automatically predict visual QoE of 3D images/videos. Firstly, we create a new subjective 3D-IQA database that has two features that are lacking in the literature, i.e., the inclusion of both 2D and 3D images, and the inclusion of mixed distortion types. We observe strong distortion type dependent bias when using the direct average of 2D image quality to predict 3D image quality. We propose a binocular rivalry inspired multi-scale model to predict the quality of stereoscopic images and the results show that the proposed model eliminates the prediction bias, leading to significantly improved quality predictions. Second, we carry out two subjective studies on depth perception of stereoscopic 3D images. The first one follows a traditional framework where subjects are asked to rate depth quality directly on distorted stereopairs. The second one uses a novel approach, where the stimuli are synthesized independent of the background image content and the subjects are asked to identify depth changes and label the polarities of depth. Our analysis shows that the second approach is much more effective at singling out the contributions of stereo cues in depth perception. We initialize the notion of depth perception difficulty index (DPDI) and propose a novel computational model for DPDI prediction. The results show that the proposed model leads to highly promising DPDI prediction performance. Thirdly, we carry out subjective 3D-VQA experiments on two databases that contain various asymmetrically compressed stereoscopic 3D videos. We then compare different mixed-distortions asymmetric stereoscopic video coding schemes with symmetric coding methods and verify their potential coding gains. We propose a model to account for the prediction bias from using direct averaging of 2D video quality to predict 3D video quality. The results show that the proposed model leads to significantly improved quality predictions and can help us predict the coding gain of mixed-distortions asymmetric video compression. Fourthly, we investigate the problem of objective quality assessment of Multi-view-plus-depth (MVD) images, with a main focus on the pre- depth-image-based-rendering (pre-DIBR) case. We find that existing IQA methods are difficult to be employed as a guiding criterion in the optimization of MVD video coding and transmission systems when applied post-DIBR. We propose a novel pre-DIBR method based on information content weighting of both texture and depth images, which demonstrates competitive performance against state-of-the-art IQA models applied post-DIBR

Gradient-based image and video quality assessment

У овој дисертацији разматране су објективне мере процене квалитета слике и видеа са потпуним и делимичним референцирањем на изворни сигнал. За потребе евалуације квалитета развијене су поуздане, рачунски ефикасне мере, засноване на очувању информација о градијенту. Мере су тестиране на великом броју тест слика и видео секвенци, различитих типова и степена деградације. Поред јавно доступних база слика и видео секвенци, за потребе истраживања формиране су и нове базе видео секвенци са преко 300 релевантних тест узорака. Поређењем доступних субјективних и објективних скорова квалитета показано је да је објективна евалуација квалитета веома сложен проблем, али га је могуће решити и доћи до високих перформанси коришћењем предложених мера процене квалитета слике и видеа.U ovoj disertaciji razmatrane su objektivne mere procene kvaliteta slike i videa sa potpunim i delimičnim referenciranjem na izvorni signal. Za potrebe evaluacije kvaliteta razvijene su pouzdane, računski efikasne mere, zasnovane na očuvanju informacija o gradijentu. Mere su testirane na velikom broju test slika i video sekvenci, različitih tipova i stepena degradacije. Pored javno dostupnih baza slika i video sekvenci, za potrebe istraživanja formirane su i nove baze video sekvenci sa preko 300 relevantnih test uzoraka. Poređenjem dostupnih subjektivnih i objektivnih skorova kvaliteta pokazano je da je objektivna evaluacija kvaliteta veoma složen problem, ali ga je moguće rešiti i doći do visokih performansi korišćenjem predloženih mera procene kvaliteta slike i videa.This thesis presents an investigation into objective image and video quality assessment with full and reduced reference on original (source) signal. For quality evaluation purposes, reliable, computational efficient, gradient-based measures are developed. Proposed measures are tested on different image and video datasets, with various types of distorsions and degradation levels. Along with publicly available image and video quality datasets, new video quality datasets are maded, with more than 300 relevant test samples. Through comparison between available subjective and objective quality scores it has been shown that objective quality evaluation is highly complex problem, but it is possible to resolve it and acchieve high performance using proposed quality measures