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  • 1.
    Minhas, Tahir Nawaz
    et al.
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för kommunikationssystem.
    Shahid, Muhammad
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Lövström, Benny
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Rossholm, Andreas
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för kommunikationssystem.
    Fiedler, Markus
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för kommunikationssystem.
    QoE rating performance evaluation of ITU-T recommended video quality metrics in the context of video freezes2016Inngår i: Australian Journal of Electrical and Electronics Engineering, ISSN 1448-837X, Vol. 13, nr 2, s. 122-131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In real-time video streaming, video quality can be degraded due to network performance issues. Among other artefacts, video freezing and video jumping are factors that influence user experience. Service providers, operators and manufacturers are interested in evaluating the quality of experience (QoE) objectively because subjective assessment of QoE is expensive and, in many user cases, subjective assessment is not possible to perform. Different algorithms have been proposed and implemented in this regard. Some of them are in the recommendation list of the ITU Telecommunication Standardization Sector (ITU-T). In this paper, we study the effect of the freezing artefact on user experience and compare the mean opinion score of these videos with the results of two algorithms, the perceptual evaluation of video quality (PEVQ) and temporal quality metric (TQM). Both metrics are part of the ITU-T Recommendation J.247 Annex B and C. PEVQ is a full-reference video quality metric, whereas TQM is a no-reference quality metric. Another contribution of this paper is the study of the impact of different resolutions and frame rates on user experience and how accurately PEVQ and TQM measure varying frame rates.

  • 2.
    Rossholm, Andreas
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    On Enhancement and Quality Assessment of Audio and Video in Communication Systems2014Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The use of audio and video communication has increased exponentially over the last decade and has gone from speech over GSM to HD resolution video conference between continents on mobile devices. As the use becomes more widespread the interest in delivering high quality media increases even on devices with limited resources. This includes both development and enhancement of the communication chain but also the topic of objective measurements of the perceived quality. The focus of this thesis work has been to perform enhancement within speech encoding and video decoding, to measure influence factors of audio and video performance, and to build methods to predict the perceived video quality. The audio enhancement part of this thesis addresses the well known problem in the GSM system with an interfering signal generated by the switching nature of TDMA cellular telephony. Two different solutions are given to suppress such interference internally in the mobile handset. The first method involves the use of subtractive noise cancellation employing correlators, the second uses a structure of IIR notch filters. Both solutions use control algorithms based on the state of the communication between the mobile handset and the base station. The video enhancement part presents two post-filters. These two filters are designed to improve visual quality of highly compressed video streams from standard, block-based video codecs by combating both blocking and ringing artifacts. The second post-filter also performs sharpening. The third part addresses the problem of measuring audio and video delay as well as skewness between these, also known as synchronization. This method is a black box technique which enables it to be applied on any audiovisual application, proprietary as well as open standards, and can be run on any platform and over any network connectivity. The last part addresses no-reference (NR) bitstream video quality prediction using features extracted from the coded video stream. Several methods have been used and evaluated: Multiple Linear Regression (MLR), Artificial Neural Network (ANN), and Least Square Support Vector Machines (LS-SVM), showing high correlation with both MOS and objective video assessment methods as PSNR and PEVQ. The impact from temporal, spatial and quantization variations on perceptual video quality has also been addressed, together with the trade off between these, and for this purpose a set of locally conducted subjective experiments were performed.

  • 3.
    Rossholm, Andreas
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Lövström, Benny
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    A robust method for estimating synchronization and delay of audio and video for communication services2016Inngår i: Multimedia tools and applications, ISSN 1380-7501, E-ISSN 1573-7721, Vol. 75, nr 1, s. 527-545Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the main contributions to the quality of experience in streaming services or in two-way communication of audio and video applications is synchronization. This has been shown in several studies and experiments but methods to measure synchronization are less frequent, especially for situations without internal access to the application and independent of platform and device. In this paper we present a method for measuring synchronization skewness as well as delay for audio and video. The solution incorporates audio and video reference streams, where audio and video frames are marked with frame numbers which are decoded on the receiver side to enable calculation of synchronization and delay. The method has been verified in a two-way communication application in a transparent network with and without inserting known delays, as well as in a network with 5 and 10 % packet loss levels. The method can be used for both streaming and two-way communication services, both with and without access to the internal structures, and enables measurements of applications running on e.g. smartphones, tablets, and laptops under various conditions.

  • 4.
    Rossholm, Andreas
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Shahid, Muhammad
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Lövström, Benny
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Analysis of the impact of temporal, spatial, and quantization variations on perceptual video quality2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The growing consumer interest in video communication has increased the users' awareness in the visual quality of the delivered media. This in turn increases, at the service provider end, the need for intelligent methodologies of optimal techniques for adapting to varying network conditions. Recent studies show that constraints on the bandwidth of transmission media should not always be translated to an increase in compression ratio to lower the bitrate of the video. Instead, a suitable option for adaptive streaming is to scale down the video temporally or spatially before encoding to maintain a desirable level of perceptual quality, while the viewing resolution is constant. Most of the existing studies to examine these scenarios are either limited to low resolution videos or lack in provisioning of subjective assessment of quality. We present here the results of our campaign of subjective quality assessment experiments done on a range of spatial and temporal resolutions, up to VGA and 30 frames per second respectively, under a number of bitrate conditions. The analysis shows, among other things, that keeping the spatial resolution is perceptually preferred among the three parameters that have impact on the video quality, even in the case with high temporal activity.

  • 5.
    Shahid, Muhammad
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Pandremmenou,, Katerina
    Univ Ioannina, GRC.
    Lisimachos P., Kondi
    Univ Ioannina, GRC.
    Andreas, Rossholm
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Lövström, Benny
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Perceptual quality estimation of H.264/AVC videos using reduced-reference and no-reference models2016Inngår i: Journal of Electronic Imaging (JEI), ISSN 1017-9909, E-ISSN 1560-229X, Vol. 25, nr 5Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reduced-reference (RR) and no-reference (NR) models for video quality estimation, using featuresthat account for the impact of coding artifacts, spatio-temporal complexity, and packet losses, are proposed. Thepurpose of this study is to analyze a number of potentially quality-relevant features in order to select the mostsuitable set of features for building the desired models. The proposed sets of features have not been used in theliterature and some of the features are used for the first time in this study. The features are employed by the leastabsolute shrinkage and selection operator (LASSO), which selects only the most influential of them toward per-ceptual quality. For comparison, we apply feature selection in the complete feature sets and ridge regression onthe reduced sets. The models are validated using a database of H.264/AVC encoded videos that were subjec-tively assessed for quality in an ITU-T compliant laboratory. We infer that just two features selected by RRLASSO and two bitstream-based features selected by NR LASSO are able to estimate perceptual qualitywith high accuracy, higher than that of ridge, which uses more features. The comparisons with competingworks and two full-reference metrics also verify the superiority of our models.

  • 6.
    Shahid, Muhammad
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Rossholm, Andreas
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Lövström, Benny
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    A No-Reference Machine Learning Based Video Quality Predictor2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The growing need of quick and online estimation of video quality necessitates the study of new frontiers in the area of no-reference visual quality assessment. Bitstream-layer model based video quality predictors use certain visual quality relevant features from the encoded video bitstream to estimate the quality. Contemporary techniques vary in the number and nature of features employed and the use of prediction model. This paper proposes a prediction model with a concise set of bitstream based features and a machine learning based quality predictor. Several full reference quality metrics are predicted using the proposed model with reasonably good levels of accuracy, monotonicity and consistency.

  • 7.
    Shahid, Muhammad
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Rossholm, Andreas
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Lövström, Benny
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för tillämpad signalbehandling.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för kommunikationssystem.
    No-reference image and video quality assessment: a classification and review of recent approaches2014Inngår i: EURASIP Journal on Image and Video Processing, ISSN 1687-5176, E-ISSN 1687-5281, Vol. 2014, nr 40Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    The field of perceptual quality assessment has gone through a wide range of developments and it is still growing. In particular, the area of no-reference (NR) image and video quality assessment has progressed rapidly during the last decade. In this article, we present a classification and review of latest published research work in the area of NR image and video quality assessment. The NR methods of visual quality assessment considered for review are structured into categories and subcategories based on the types of methodologies used for the underlying processing employed for quality estimation. Overall, the classification has been done into three categories, namely, pixel-based methods, bitstream-based methods, and hybrid methods of the aforementioned two categories. We believe that the review presented in this article will be helpful for practitioners as well as for researchers to keep abreast of the recent developments in the area of NR image and video quality assessment. This article can be used for various purposes such as gaining a structured overview of the field and to carry out performance comparisons for the state-of-the-art methods.

  • 8.
    Shahid, Muhammad
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Singam, Amitesh Kumar
    Rossholm, Andreas
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Lövstrom, Benny
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Subjective Quality Assessment of H.264/AVC Encoded Low Resolution Videos2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Advancements in the video processing area have been proliferated by services that require low delay. Such services involve applications being offered at various temporal and spatial resolutions. It necessitates to study the impacts of related video coding conditions upon perceptual quality. But most of studies concerned with quality assessment of videos affected by coding distortions lack in variety of spatio-temporal resolutions. This paper presents a work done on quality assessment of videos encoded by state-of-the-art H.264/AVC standard at different bitrates and frame rates. Overall, 120 test scenarios for video sequences having different spatial and temporal spectral information were studied. The used coded bistreams in this work and the corresponding subjective assessment scores have been made public for the research community to facilitate further studies

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