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Lydia Meesters

Bio: Lydia Meesters is an academic researcher from Eindhoven University of Technology. The author has contributed to research in topics: Video quality & Subjective video quality. The author has an hindex of 4, co-authored 12 publications receiving 560 citations.

Papers
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Journal ArticleDOI
TL;DR: The perceptual requirements for 3-D TV that can be extracted from the literature are summarized and issues that require further investigation are addressed in order for 3D TV to be a success.
Abstract: A high-quality three-dimensional (3-D) broadcast service (3-D TV) is becoming increasingly feasible based on various recent technological developments combined with an enhanced understanding of 3-D perception and human factors issues surrounding 3-D TV. In this paper, 3-D technology and perceptually relevant issues, in particular 3-D image quality and visual comfort, in relation to 3-D TV systems are reviewed. The focus is on near-term displays for broadcast-style single- and multiple-viewer systems. We discuss how an image quality model for conventional two-dimensional images needs to be modified to be suitable for image quality research for 3-D TV. In this respect, studies are reviewed that have focused on the relationship between subjective attributes of 3-D image quality and physical system parameters that induce them (e.g., parameter choices in image acquisition, compression, and display). In particular, artifacts that may arise in 3-D TV systems are addressed, such as keystone distortion, depth-plane curvature, puppet theater effect, cross talk, cardboard effect, shear distortion, picket-fence effect, and image flipping. In conclusion, we summarize the perceptual requirements for 3-D TV that can be extracted from the literature and address issues that require further investigation in order for 3-D TV to be a success.

333 citations

Journal ArticleDOI
01 Apr 2006
TL;DR: Results on asymmetric and symmetric coding showed that the relationship between perceived image quality and average bit rate is not straightforward, and in some cases, image quality ratings of a symmetric coded pair can be higher than for an asymmetriccoded pair, even if the averaged bit rate for the symmetric pair is lower, than for the asymmetric pair.
Abstract: JPEG compression of the left and right components of a stereo image pair is a way to save valuable bandwidth when transmitting stereoscopic images. This paper presents results on the effects of camera-base distance (B) and JPEG coding on overall image quality, perceived depth, perceived sharpness, and perceived eye strain. In the experiment, two stereoscopic still scenes were used, varying in depth (three different camera-base distances: 0, 8, and 12 cm) and compression ratio (4 levels: original, 1:30, 1:40, and 1:60). All levels of compression were applied to both the left and right stereo image, resulting in a 4 × 4 matrix of all possible symmetric and asymmetric coding combinations. The observers were asked to assess image quality, sharpness, depth, and eye strain. Results showed that an increase in JPEG coding had a negative effect on image quality, sharpness, and eye strain, but had no effect on perceived depth. An increase in camera-base distance increased perceived depth and reported eye strain, but had no effect on perceived sharpness. Results on asymmetric and symmetric coding showed that the relationship between perceived image quality and average bit rate is not straightforward. In some cases, image quality ratings of a symmetric coded pair can be higher than for an asymmetric coded pair, even if the averaged bit rate for the symmetric pair is lower, than for the asymmetric pair. Furthermore, sharpness and eye strain correlated highly and medium, respectively, with perceived image quality.

188 citations

Book ChapterDOI
09 Dec 2009
TL;DR: In this paper, a generic framework for evaluating the user experience using both subjective and objective measures of user experience is proposed, which will be tested and validated in the large-scale field trials of the FP7 MyMedia project.
Abstract: Providing useful recommendations is an important challenge for user-centric media systems. Whereas current recommender systems research mainly focuses on predictive accuracy, we contend that a truly user-centric approach to media recommendations requires the inclusion of user experience measurement. For a good experience, predictive accuracy is not enough. What users like and dislike about our systems is also determined by usage context and individual user characteristics. We therefore propose a generic framework for evaluating the user experience using both subjective and objective measures of user experience. We envision the framework, which will be tested and validated in the large-scale field trials of the FP7 MyMedia project, to be a fundamental step beyond accuracy of algorithms, towards usability of recommender systems.

17 citations

Proceedings ArticleDOI
24 May 2007
TL;DR: This research looked at the difference in perceived video quality between I-Frame Delay (temporal scaling) and TransCoding (quality scaling), and results show that I- Frame Delay scored better for video content without a lot of background movement, while TransCoded was scoring better for scenes with lot of Background movement.
Abstract: Developing a content-aware coding scheme that delivers ensured QoE for end-users includes finding out which content information will be most needed; especially when wireless networks are used to send video information. Wireless in-home networks suffer from interference which creates variable throughput, which causes problems when sending video material from one device to another. Temporal and quality scaling provide classes for video adaptation methods that can handle this variable throughput. Presented research concerns the effect of temporal scaling versus quality scaling on different kinds of video content. We looked at the difference in perceived video quality between I-Frame Delay (temporal scaling) and TransCoding (quality scaling). Results show that I-Frame Delay scored better for video content without a lot of background movement, while TransCoding was scored better for scenes with lot of background movement. There are also indications that information about scene changes can be helpful to create content-aware coding.

17 citations

Proceedings ArticleDOI
14 Feb 2008
TL;DR: The main result indicates that participants generally rated spatial distortions as better video quality than the same video sequence containing temporal distortions; even though video sequences containing spatial distortions were coded at an overall lower bitrate than video sequencescontaining temporal distortions.
Abstract: This paper describes an experiment that studies perceived video quality, with the goal to get a better understanding of whether a temporal or a spatial MPEG-2 based adaptation method should be used for video transmission over variable bandwidth. The research focused on the relation between in-scene motion and camera motion on spatial as well as temporal distortions in video sequences. Participants were tested on their sensitivity and appreciation for spatial and temporal distortions using the scale paradigm of direct comparison. Footage was shot to create video material of three scenes with a systematic manipulation of in-scene motion and camera motion, which produced twelve different video sequences. Results show a relation trend between the two types of motion and the two types of distortion in video sequences. The main result indicates that participants generally rated spatial distortions as better video quality than the same video sequence containing temporal distortions; even though video sequences containing spatial distortions were coded at an overall lower bitrate than video sequences containing temporal distortions.

3 citations


Cited by
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Journal ArticleDOI
TL;DR: The importance of various causes and aspects of visual discomfort is clarified and three-dimensional artifacts resulting from insufficient depth information in the incoming data signal yielding spatial and temporal inconsistencies are believed to be the most pertinent.
Abstract: Visual discomfort has been the subject of considerable research in relation to stereoscopic and autostereoscopic displays. In this paper, the importance of various causes and aspects of visual discomfort is clarified. When disparity values do not surpass a limit of 1°, which still provides sufficient range to allow satisfactory depth perception in stereoscopic television, classical determinants such as excessive binocular parallax and accommodation-vergence conflict appear to be of minor importance. Visual discomfort, however, may still occur within this limit and we believe the following factors to be the most pertinent in contributing to this: (1) temporally changing demand of accommodation-vergence linkage, e.g., by fast motion in depth; (2) three-dimensional artifacts resulting from insufficient depth information in the incoming data signal yielding spatial and temporal inconsistencies; and (3) unnatural blur. In order to ad- equately characterize and understand visual discomfort, multiple types of measurements, both objective and subjective, are required. © 2009 Society for Imaging Science and Technology. DOI: 10.2352/J.ImagingSci.Technol.2009.53.3.030201

990 citations

Journal ArticleDOI
TL;DR: A systematic, comprehensive and up-to-date review of perceptual visual quality metrics (PVQMs) to predict picture quality according to human perception.

895 citations

Journal ArticleDOI
TL;DR: The technical development of HAS, existing open standardized solutions, but also proprietary solutions are reviewed in this paper as fundamental to derive the QoE influence factors that emerge as a result of adaptation.
Abstract: Changing network conditions pose severe problems to video streaming in the Internet. HTTP adaptive streaming (HAS) is a technology employed by numerous video services that relieves these issues by adapting the video to the current network conditions. It enables service providers to improve resource utilization and Quality of Experience (QoE) by incorporating information from different layers in order to deliver and adapt a video in its best possible quality. Thereby, it allows taking into account end user device capabilities, available video quality levels, current network conditions, and current server load. For end users, the major benefits of HAS compared to classical HTTP video streaming are reduced interruptions of the video playback and higher bandwidth utilization, which both generally result in a higher QoE. Adaptation is possible by changing the frame rate, resolution, or quantization of the video, which can be done with various adaptation strategies and related client- and server-side actions. The technical development of HAS, existing open standardized solutions, but also proprietary solutions are reviewed in this paper as fundamental to derive the QoE influence factors that emerge as a result of adaptation. The main contribution is a comprehensive survey of QoE related works from human computer interaction and networking domains, which are structured according to the QoE impact of video adaptation. To be more precise, subjective studies that cover QoE aspects of adaptation dimensions and strategies are revisited. As a result, QoE influence factors of HAS and corresponding QoE models are identified, but also open issues and conflicting results are discussed. Furthermore, technical influence factors, which are often ignored in the context of HAS, affect perceptual QoE influence factors and are consequently analyzed. This survey gives the reader an overview of the current state of the art and recent developments. At the same time, it targets networking researchers who develop new solutions for HTTP video streaming or assess video streaming from a user centric point of view. Therefore, this paper is a major step toward truly improving HAS.

746 citations

Journal ArticleDOI
TL;DR: This paper proposes a framework that takes a user-centric approach to recommender system evaluation that links objective system aspects to objective user behavior through a series of perceptual and evaluative constructs (called subjective system aspects and experience, respectively).
Abstract: Research on recommender systems typically focuses on the accuracy of prediction algorithms. Because accuracy only partially constitutes the user experience of a recommender system, this paper proposes a framework that takes a user-centric approach to recommender system evaluation. The framework links objective system aspects to objective user behavior through a series of perceptual and evaluative constructs (called subjective system aspects and experience, respectively). Furthermore, it incorporates the influence of personal and situational characteristics on the user experience. This paper reviews how current literature maps to the framework and identifies several gaps in existing work. Consequently, the framework is validated with four field trials and two controlled experiments and analyzed using Structural Equation Modeling. The results of these studies show that subjective system aspects and experience variables are invaluable in explaining why and how the user experience of recommender systems comes about. In all studies we observe that perceptions of recommendation quality and/or variety are important mediators in predicting the effects of objective system aspects on the three components of user experience: process (e.g. perceived effort, difficulty), system (e.g. perceived system effectiveness) and outcome (e.g. choice satisfaction). Furthermore, we find that these subjective aspects have strong and sometimes interesting behavioral correlates (e.g. reduced browsing indicates higher system effectiveness). They also show several tradeoffs between system aspects and personal and situational characteristics (e.g. the amount of preference feedback users provide is a tradeoff between perceived system usefulness and privacy concerns). These results, as well as the validated framework itself, provide a platform for future research on the user-centric evaluation of recommender systems.

651 citations

Journal ArticleDOI
TL;DR: A quality metric for the assessment of stereopairs is proposed using the fusion of 2D quality metrics and of the depth information and is evaluated using the SAMVIQ methodology for subjective assessment.
Abstract: Several metrics have been proposed in literature to assess the perceptual quality of two-dimensional images. However, no similar effort has been devoted to quality assessment of stereoscopic images. Therefore, in this paper, we review the different issues related to 3D visualization, and we propose a quality metric for the assessment of stereopairs using the fusion of 2D quality metrics and of the depth information. The proposed metric is evaluated using the SAMVIQ methodology for subjective assessment. Specifically, distortions deriving from coding are taken into account and the quality degradation of the stereopair is estimated by means of subjective tests.

391 citations