The Experts below are selected from a list of 131751 Experts worldwide ranked by ideXlab platform
Touradj Ebrahimi - One of the best experts on this subject based on the ideXlab platform.
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towards Subjective Quality assessment of point cloud imaging in augmented reality
Multimedia Signal Processing, 2017Co-Authors: Evangelos Alexiou, Evgeniy Upenik, Touradj EbrahimiAbstract:Recently, there has been an increased interest in capture, processing and rendering of visual content in form of point clouds. Among other challenges, Subjective and objective Quality assessments of point clouds are still open problems. Most proposed Subjective Quality evaluation methodologies are variants or extensions of counter parts from conventional approaches such as those proposed in various ITU-R and ITU-T recommendations. A key issue with point cloud content is that of rendering and display devices which are thoroughly different from those in other modalities in addition to novel applications which depart from traditional display devices. In this paper, we propose a radically different approach to point cloud Subjective Quality assessment for point cloud by making use of augmented reality head mounted displays. Beside description of the approach, we show examples of implementation of the proposed methodology and draw conclusions regarding its advantages and drawbacks. Finally, the proposed approach is used in assessing the performance of widely used objective metrics to compute Quality of point cloud contents when they undergo various types of distortions such as corruption by noise, simplification and compression.
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Subjective Quality assessment database of hdr images compressed with jpeg xt
Quality of Multimedia Experience, 2015Co-Authors: Pavel Korshunov, Philippe Hanhart, Thomas Richter, Alessandro Artusi, Rafal Mantiuk, Touradj EbrahimiAbstract:Recent advances in high dynamic range (HDR) capturing and display technologies attracted a lot of interest to HDR imaging. Many issues that are considered as being resolved for conventional low dynamic range (LDR) images pose new challenges in HDR context. One such issue is a lack of standards for HDR image compression. Another is the limited availability of suitable image datasets that are suitable for studying and evaluation of HDR image compression. In this paper, we address this problem by creating a publicly available dataset of 20 HDR images and corresponding versions compressed at four different bit rates with three profiles of the upcoming JPEG XT standard for HDR image compression. The images cover different scenes, dynamic ranges, and acquisition methods (fusion from several exposures, frame of an HDR video, and CGI generated images). The dataset also includes Mean Opinion Scores (MOS) for each compressed version of the images obtained from extensive Subjective experiments using SIM2 HDR monitor.
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Calculation of average coding efficiency based on Subjective Quality scores
Journal of Visual Communication and Image Representation, 2014Co-Authors: Philippe Hanhart, Touradj EbrahimiAbstract:The Bjontegaard model is widely used to calculate the coding efficiency between different codecs. However, this model might not be an accurate predictor of the true coding efficiency as it relies on PSNR measurements. Therefore, in this paper, we propose a model to calculate the average coding efficiency based on Subjective Quality scores, i.e., mean opinion scores (MOS). We call this approach Subjective Comparison of ENcoders based on fItted Curves (SCENIC). To consider the intrinsic nature of bounded rating scales, a logistic function is used to fit the rate-distortion (R-D) values. The average MOS and bit rate differences are computed between the fitted R-D curves. The statistical property of Subjective scores is considered to estimate corresponding confidence intervals on the calculated average MOS and bit rate differences. The proposed model is expected to report more realistic coding efficiency as PSNR is not always correlated with perceived visual Quality.
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Paired comparison-based Subjective Quality assessment of stereoscopic images
Multimedia Tools and Applications, 2013Co-Authors: Lutz Goldmann, Touradj EbrahimiAbstract:As 3D image and video content has gained significant popularity, Subjective 3D Quality assessment has become an important issue for the creation, processing, and distribution of high Quality 3D content. Reliable Subjective Quality assessment of 3D content is often difficult due to the subjects’ limited 3D experience, the interaction of multiple Quality factors, minor Quality differences between stimuli, etc. Among Subjective evaluation methodologies, paired comparison has the advantage of improved simplicity and reliability, which can be useful to tackle the aforementioned difficulties. In this paper, we propose a new method to analyze the results of paired comparison-based Subjective tests. We assume that ties convey information about the significance of Quality score differences between two stimuli. Then, a maximum likelihood estimation is performed to obtain confidence intervals providing intuitive measures of significance of the Quality differences. We describe the complete test procedure using the proposed method, from Subjective experiment design to outlier detection and score analysis for 3D image Quality assessment. Especially, we design the test procedure in a way that Quality comparison across different contents is enabled while the number of pair-wise comparisons is minimized. Experimental results on a stereoscopic image database with varying camera distances demonstrate the usefulness of the proposed method and enhanced Quality discriminability of paired comparison in comparison to the conventional single stimulus methodology.
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OBJECTIVE Quality METRICS FOR VIDEO SCALABILITY
2013Co-Authors: Adrien Besson, Francesca De Simone, Touradj EbrahimiAbstract:Scalable video coding is emerging as an efficient alternative to simulcast encoding to distribute the same video content simultaneously to many users having different terminals and network conditions. In order to select the best combination of video scalability options for a given network condition and content, the availability of objective metrics that can reliably predict the video Quality of scalable video sequence is crucial. In this paper, we propose a performance evaluation study of a set of state of the art Full-Reference and No-Reference metrics, considering a public database of test video sequences and related Subjective Quality annotations. The results demonstrate that most of the considered metrics show lack of robustness as predictors of Subjective Quality when both spatial and temporal Quality distortions occur.
Alan C. Bovik - One of the best experts on this subject based on the ideXlab platform.
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Study of Subjective Quality and Objective Blind Quality Prediction of Stereoscopic Videos
IEEE transactions on image processing : a publication of the IEEE Signal Processing Society, 2019Co-Authors: Balasubramanyam Appina, Sumohana Et. Al Channappayya, Sathya Veera Reddy Dendi, K. Manasa, Alan C. BovikAbstract:We present a new Subjective and objective study on full high-definition (HD) stereoscopic (3D or S3D) video Quality. In the Subjective study, we constructed an S3D video dataset with 12 pristine and 288 test videos, and the test videos are generated by applying the H.264 and H.265 compression, blur, and frame freeze artifacts. We also propose a no reference (NR) objective video Quality assessment (QA) algorithm that relies on measurements of the statistical dependencies between the motion and disparity subband coefficients of S3D videos. Inspired by the Generalized Gaussian Distribution (GGD) approach, we model the joint statistical dependencies between the motion and disparity components as following a Bivariate Generalized Gaussian Distribution (BGGD). We estimate the BGGD model parameters ( $\alpha,\,\beta $ ) and the coherence measure ( $\Psi $ ) from the eigenvalues of the sample covariance matrix (M) of the BGGD. In turn, we model the BGGD parameters of pristine S3D videos using a Multivariate Gaussian (MVG) distribution. The likelihood of a test video’s MVG model parameters coming from the pristine MVG model is computed and shown to play a key role in the overall Quality estimation. We also estimate the global motion content of each video by averaging the SSIM scores between pairs of successive video frames. To estimate the test S3D video’s spatial Quality, we apply the popular 2D NR unsupervised NIQE image QA model on a frame-by-frame basis on both views. The overall Quality of a test S3D video is finally computed by pooling the test S3D video’s likelihood estimates, global motion strength, and spatial Quality scores. The proposed algorithm, which is completely blind (requiring no reference videos or training on Subjective scores) is called the Motion and Disparity-based 3D video Quality evaluator (MoDi3D). We show that MoDi3D delivers competitive performance over a wide variety of datasets, including the IRCCYN dataset, the WaterlooIVC Phase I dataset, the LFOVIA dataset, and our proposed LFOVIAS3DPh2 S3D video dataset.
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a time varying Subjective Quality model for mobile streaming videos with stalling events
Proceedings of SPIE, 2015Co-Authors: Deepti Ghadiyaram, Janice Pan, Alan C. BovikAbstract:Over-the-top mobile video streaming is invariably influenced by volatile network conditions which cause playback interruptions (stalling events), thereby impairing users' Quality of experience (QoE). Developing models that can accurately predict users' QoE could enable the more efficient design of Quality-control protocols for video streaming networks that reduce network operational costs while still delivering high-Quality video content to the customers. Existing objective models that predict QoE are based on global video features, such as the number of stall events and their lengths, and are trained and validated on a small pool of ad hoc video datasets, most of which are not publicly available. The model we propose in this work goes beyond previous models as it also accounts for the fundamental effect that a viewer's recent level of satisfaction or dissatisfaction has on their overall viewing experience. In other words, the proposed model accounts for and adapts to the recency, or hysteresis effect caused by a stall event in addition to accounting for the lengths, frequency of occurrence, and the positions of stall events - factors that interact in a complex way to affect a user's QoE. On the recently introduced LIVE-Avvasi Mobile Video Database, which consists of 180 distorted videos of varied content that are afflicted solely with over 25 unique realistic stalling events, we trained and validated our model to accurately predict the QoE, attaining standout QoE prediction performance.
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Rate Adaptation and Admission Control for Video Transmission With Subjective Quality Constraints
IEEE Journal of Selected Topics in Signal Processing, 2015Co-Authors: Chao Chen, Gustavo De Veciana, Alan C. Bovik, Robert W. HeathAbstract:Adapting video data rate during streaming can effectively reduce the risk of playback interruptions caused by channel throughput fluctuations. The variations in rate, however, also introduce video Quality fluctuations and thus potentially affects viewers' Quality of Experience (QoE). We show how the QoE of video users can be improved by rate adaptation and admission control. We conducted a Subjective study wherein we found that viewers' QoE was strongly correlated with the empirical cumulative distribution function (eCDF) of the predicted video Quality. Based on this observation, we propose a rate-adaptation algorithm that can incorporate QoE constraints on the empirical cumulative Quality distribution per user. We then propose a threshold-based admission control policy to block users whose empirical cumulative Quality distribution is not likely to satisfy their QoE constraint. We further devise an online adaptation algorithm to automatically optimize the threshold. Extensive simulation results show that the proposed scheme can reduce network resource consumption by 40% over conventional average-Quality maximized rate-adaptation algorithms.
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modeling the time varying Subjective Quality of http video streams with rate adaptations
IEEE Transactions on Image Processing, 2014Co-Authors: Chao Chen, Gustavo De Veciana, Robert W. Heath, Lark Kwon Choi, Constantine Caramanis, Alan C. BovikAbstract:Newly developed hypertext transfer protocol (HTTP)-based video streaming technologies enable flexible rate-adaptation under varying channel conditions. Accurately predicting the users' Quality of experience (QoE) for rate-adaptive HTTP video streams is thus critical to achieve efficiency. An important aspect of understanding and modeling QoE is predicting the up-to-the-moment Subjective Quality of a video as it is played, which is difficult due to hysteresis effects and nonlinearities in human behavioral responses. This paper presents a Hammerstein-Wiener model for predicting the time-varying Subjective Quality (TVSQ) of rate-adaptive videos. To collect data for model parameterization and validation, a database of longer duration videos with time-varying distortions was built and the TVSQs of the videos were measured in a large-scale Subjective study. The proposed method is able to reliably predict the TVSQ of rate adaptive videos. Since the Hammerstein-Wiener model has a very simple structure, the proposed method is suitable for online TVSQ prediction in HTTP-based streaming.
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modeling the time varying Subjective Quality of http video streams with rate adaptations
arXiv: Multimedia, 2013Co-Authors: Chao Chen, Gustavo De Veciana, Robert W. Heath, Lark Kwon Choi, Constantine Caramanis, Alan C. BovikAbstract:Newly developed HTTP-based video streaming technologies enable flexible rate-adaptation under varying channel conditions. Accurately predicting the users' Quality of Experience (QoE) for rate-adaptive HTTP video streams is thus critical to achieve efficiency. An important aspect of understanding and modeling QoE is predicting the up-to-the-moment Subjective Quality of a video as it is played, which is difficult due to hysteresis effects and nonlinearities in human behavioral responses. This paper presents a Hammerstein-Wiener model for predicting the time-varying Subjective Quality (TVSQ) of rate-adaptive videos. To collect data for model parameterization and validation, a database of longer-duration videos with time-varying distortions was built and the TVSQs of the videos were measured in a large-scale Subjective study. The proposed method is able to reliably predict the TVSQ of rate adaptive videos. Since the Hammerstein-Wiener model has a very simple structure, the proposed method is suitable for on-line TVSQ prediction in HTTP based streaming.
Lars Hansson - One of the best experts on this subject based on the ideXlab platform.
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structured patient clinician communication and 1 year outcome in community mental healthcare cluster randomised controlled trial
British Journal of Psychiatry, 2007Co-Authors: Stefan Priebe, Rosemarie Mccabe, Lars Hansson, Jens Bullenkamp, Christoph Lauber, Rafael Martinezleal, Wulf Rossler, Hans Joachim Salize, Bengt Svensson, Francisco TorresgonzalesAbstract:Background Patient-clinician communication is central to mental healthcare but neglected in research. Aims To testa new computer-mediated intervention structuring patient-clinician dialogue (DIALOG) focusing on patients' Quality of life and needs for care. Method In a cluster randomised controlled trial, 134 key workers in six countries were allocated to DIALOG or treatment as usual; 507 people with schizophrenia or related disorders were included. Every 2 months for I year, clinicians asked patients to rate satisfaction with Quality of life and treatment, and request additional or different support. Responses were fed back immediately in screen displays, compared with previous ratings and discussed. Primary outcome was Subjective Quality of life, and secondary outcomes were unmet needs and treatment satisfaction. Results Of 507 patients, 56 were lost to follow-up and 451 were included in intention-to-treat analyses. Patients receiving the DIALOG intervention had better Subjective Quality of life, fewer unmet needs and higher treatment satisfaction after 12 months. Conclusions Structuring patient clinician dialogue to focus on patients' views positively influenced Quality of life, needs for care and treatment satisfaction.
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quantitative and qualitative aspects of the social network in schizophrenic patients living in the community relationship to sociodemographic characteristics and clinical factors and Subjective Quality of life
International Journal of Social Psychiatry, 2001Co-Authors: Anita Bengtssontops, Lars HanssonAbstract:Quantitative and qualitative aspects of the social network were investigated in a sample of 120 schizophrenic out-patients. Sociodemographic and clinical factors as well as Subjective Quality of life were investigated as to their relationship to the social network. The Interview Schedule for Social Integration (ISSI) was used to assess social network and Lancashire Quality of Life Profile was used to assess Subjective Quality of life. Psychopathology was measured by BPRS and psycho social functioning by GAF. The patients reported a significantly worse social network compared to a normal sample both regarding quantitative and qualitative aspects of the network. Alrnost half of the patients wanted access to more social contacts. Relatives and friends turned out to be the patient's main source of supportive contacts. More severe negative and positive symptoms were related to a worse social network. Support was found for an association between characteristics of the social network, such as satisfaction with s...
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quantitative and qualitative aspects of the social network in schizophrenic patients living in the community relationship to sociodemographic characteristics and clinical factors and Subjective Quality of life
International Journal of Social Psychiatry, 2001Co-Authors: Anita Bengtssontops, Lars HanssonAbstract:Quantitative and qualitative aspects of the social network were investigated in a sample of 120 schizophrenic out-patients. Sociodemographic and clinical factors as well as Subjective Quality of life were investigated as to their relationship to the social network. The Interview Schedule for Social Integration (ISSI) was used to assess social network and Lancashire Quality of Life Profile was used to assess Subjective Quality of life. Psychopathology was measured by BPRS and psychosocial functioning by GAF. The patients reported a significantly worse social network compared to a normal sample both regarding quantitative and qualitative aspects of the network. Almost half of the patients wanted access to more social contacts. Relatives and friends turned out to be the patient's main source of supportive contacts. More severe negative and positive symptoms were related to a worse social network. Support was found for an association between characteristics of the social network, such as satisfaction with social contacts, and Quality of life. The results give reason to suggest that the care system should consider the informal caregivers' situation and focus on interventions, which enhance the patient's satisfaction with social contacts.
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The relationship of personality dimensions as measured by the temperament and character inventory and Quality of life in individuals with schizophrenia or schizoaffective disorder living in the community
Quality of Life Research, 2001Co-Authors: Lars Hansson, Mona Eklund, Anita Bengtsson-topsAbstract:The influence of personality factors on the appraisal of Subjective Quality of life in individuals with schizophrenia or schizoaffective disorder is not much investigated. The present study examined this relationship in a sample of 104 patients living in the community. The temperament and character inventory was used to assess personality and the Lancashire Quality of life profile was used to assess Quality of life. The results showed that lower levels of harm avoidance and higher levels of self-directedness were significantly correlated to a better Subjective Quality of life. Regression analyses controlling for psychopathology revealed that a higher level of self-directedness was significantly associated with a better Subjective Quality in all aspects measured and explained the variance in the latter in the range of 4–12%. It is concluded that personality factors are involved in severely mentally ill individuals' assessment of their Quality of life and should be accounted for in evaluations of Quality of life assessments. The strength and directions of this influence require further studies.
Chao Chen - One of the best experts on this subject based on the ideXlab platform.
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Rate Adaptation and Admission Control for Video Transmission With Subjective Quality Constraints
IEEE Journal of Selected Topics in Signal Processing, 2015Co-Authors: Chao Chen, Gustavo De Veciana, Alan C. Bovik, Robert W. HeathAbstract:Adapting video data rate during streaming can effectively reduce the risk of playback interruptions caused by channel throughput fluctuations. The variations in rate, however, also introduce video Quality fluctuations and thus potentially affects viewers' Quality of Experience (QoE). We show how the QoE of video users can be improved by rate adaptation and admission control. We conducted a Subjective study wherein we found that viewers' QoE was strongly correlated with the empirical cumulative distribution function (eCDF) of the predicted video Quality. Based on this observation, we propose a rate-adaptation algorithm that can incorporate QoE constraints on the empirical cumulative Quality distribution per user. We then propose a threshold-based admission control policy to block users whose empirical cumulative Quality distribution is not likely to satisfy their QoE constraint. We further devise an online adaptation algorithm to automatically optimize the threshold. Extensive simulation results show that the proposed scheme can reduce network resource consumption by 40% over conventional average-Quality maximized rate-adaptation algorithms.
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modeling the time varying Subjective Quality of http video streams with rate adaptations
IEEE Transactions on Image Processing, 2014Co-Authors: Chao Chen, Gustavo De Veciana, Robert W. Heath, Lark Kwon Choi, Constantine Caramanis, Alan C. BovikAbstract:Newly developed hypertext transfer protocol (HTTP)-based video streaming technologies enable flexible rate-adaptation under varying channel conditions. Accurately predicting the users' Quality of experience (QoE) for rate-adaptive HTTP video streams is thus critical to achieve efficiency. An important aspect of understanding and modeling QoE is predicting the up-to-the-moment Subjective Quality of a video as it is played, which is difficult due to hysteresis effects and nonlinearities in human behavioral responses. This paper presents a Hammerstein-Wiener model for predicting the time-varying Subjective Quality (TVSQ) of rate-adaptive videos. To collect data for model parameterization and validation, a database of longer duration videos with time-varying distortions was built and the TVSQs of the videos were measured in a large-scale Subjective study. The proposed method is able to reliably predict the TVSQ of rate adaptive videos. Since the Hammerstein-Wiener model has a very simple structure, the proposed method is suitable for online TVSQ prediction in HTTP-based streaming.
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modeling the time varying Subjective Quality of http video streams with rate adaptations
arXiv: Multimedia, 2013Co-Authors: Chao Chen, Gustavo De Veciana, Robert W. Heath, Lark Kwon Choi, Constantine Caramanis, Alan C. BovikAbstract:Newly developed HTTP-based video streaming technologies enable flexible rate-adaptation under varying channel conditions. Accurately predicting the users' Quality of Experience (QoE) for rate-adaptive HTTP video streams is thus critical to achieve efficiency. An important aspect of understanding and modeling QoE is predicting the up-to-the-moment Subjective Quality of a video as it is played, which is difficult due to hysteresis effects and nonlinearities in human behavioral responses. This paper presents a Hammerstein-Wiener model for predicting the time-varying Subjective Quality (TVSQ) of rate-adaptive videos. To collect data for model parameterization and validation, a database of longer-duration videos with time-varying distortions was built and the TVSQs of the videos were measured in a large-scale Subjective study. The proposed method is able to reliably predict the TVSQ of rate adaptive videos. Since the Hammerstein-Wiener model has a very simple structure, the proposed method is suitable for on-line TVSQ prediction in HTTP based streaming.
Alexander Raake - One of the best experts on this subject based on the ideXlab platform.
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comparison of Subjective Quality evaluation for hevc encoded omnidirectional videos at different bit rates for uhd and fhd resolution
ACM Multimedia, 2017Co-Authors: Ashutosh Singla, Stephan Fremerey, Werner Robitza, Pierre Lebreton, Alexander RaakeAbstract:In this paper, we perform Subjective Quality evaluation studies for HEVC/H.265-encoded omnidirectional videos at different bit-rates for two different resolutions (FHD and UHD) on an Oculus Rift. Results of these tests provide insight into appropriate coding and resolution settings for given bitrate constraints, for example in an HTTP-based streaming (HAS) context. Subjective Quality judgements were collected on a 5-point Absolute Category Rating (ACR) scale. Further, we collected head motion data during viewing and rating. Working towards the technical goal of Subjective evaluation for different resolutions and bit-rates, we address aspects of how to conduct respective viewing tests, involving information from head-rotation tracking (yaw and pitch) and motion-sickness questionnaires. Quality adaptation (in terms of resolution and bit-rate) of omnidirectional videos is an important feature of media streaming. Its effect on Subjective Quality evaluations of 360° video has not been investigated so far. To utilize network and processing resources efficiently, limitations in the resolution of current Head Mounted Displays (HMDs), with typically 2160 x 1200 pixels per view, may be exploited. The Subjective test results provide indications for boundaries between resolution and quantization scaling. To discuss the merits of the applied Subjective test method, we compare simulator sickness scores along with behavioral data.
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Study of Rating Scales for Subjective Quality Assessment of High-Definition Video
IEEE Transactions on Broadcasting, 2011Co-Authors: Quan Huynh-thu, Marie-neige Garcia, Filippo Speranza, Philip Corriveau, Alexander RaakeAbstract:With the constant evolution of video technology and the deployment of new video services, content providers and broadcasters always face the challenge of delivering an adequate video Quality which meets end-users expectations. The development of reliable Quality testing and Quality monitoring tools that can be used by broadcasters ultimately requires reliable objective video Quality metrics. In turn, the validation of these objective models requires reliable Subjective assessment, the most accurate representation of the Quality perceived by end-users. Many different Subjective assessment methodologies exist, and each has its advantages and drawbacks. One important element in a Subjective testing methodology is the choice of the rating scale. In this paper, we make a direct comparison between four scales, which are either included in existing international standards or proposed to be used in future standardization activities related to video Quality. We examine the Subjective data from the points of view of response behavior from participants, similarity and variability of Subjective scores. We discuss these results within the context of the Subjective Quality assessment of high-definition video compressed and transmitted over error-prone networks. Our experimental data show no overall statistical differences between the different scales. Results also show that the single-stimulus presentation provides highly repeatable results even if different scales or groups of participants are used.
