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1.	Arndt, Sebastian, et al. (författare) Review on using physiology in quality of experience 2016 Ingår i: Electronic Imaging. - : The Society for Imaging Science and Technology. - 9781510827943 ; , s. 197-205 Konferensbidrag (refereegranskat)abstract In the area of Quality of Experience (QoE), one challenge is to design test methodologies in order to evaluate the perceived quality of multimedia content delivered through technical sys-tems. Traditionally, this evaluation is done using subjective opinion tests. However, sometimes it is difficult for observers to communicate the experienced quality through the given scale. Fur-thermore. those tests do not give insights into how the user is reacting on an internal physiological level. To overcome these issues, one approach is to use physiological measures, in order to derive a direct non-verbal response of the recipient. In this paper, we review studies that have been performed in the domain of QoE using physiological measures and we look into current activities in standardization bodies. We present challenges this research faces. and give an overview on what researchers should be aware of when they want to start working in this research area.
2.	Bosse, Sebastian, et al. (författare) A common framework for the evaluation of psychophysiological visual quality assessment 2019 Ingår i: Quality and User Experience. - : Springer Science and Business Media LLC. - 2366-0139 .- 2366-0147. ; 4:3 Tidskriftsartikel (refereegranskat)abstract The assessment of perceived quality based on psychophysiological methods recently gained attraction as it potentially overcomes certain flaws of psychophysical approaches. Although studies report promising results, it is not possible to arrive at decisive and comparable conclusions that recommend the use of one or another method for a specific application or research question. The video quality expert group started a project on psychophysiological quality assessment to study these novel approaches and to develop a test plan that enables more systematic research. This test plan comprises of a specifically designed set of quality annotated video sequences, suggestions for psychophysiological methods to be studied in quality assessment, and recommendations for the documentation and publications of test results. The test plan is presented in this article.
3.	Duong, Quang Trung, et al. (författare) Cooperative Wireless Communications with Unequal Error Protection and Fixed Decode-And-Forward Relays 2010 Konferensbidrag (refereegranskat)abstract In this paper, we examine an unequal error protection (UEP) scheme for wireless imaging that is based on utilizing the distributed diversity offered by decode-and-forward (DF) networks. Specifically, the data stream after source encoding is divided into high and low priority sub-streams depending on their importance for image reconstruction. A relay-selection combining (R-SC) scheme is exploited for high priority image data to achieve high reliability while cooperative spatial multiplexing is employed to low priority image data to support high spectral efficiency. In this work, we specifically take into account the setting that relays may forward erroneously detected signals to the destination when cooperating with fixed DF. In this context, the analytical and numerical results validate that R-SC outperforms other relaying protocols in terms of average symbol error probability while the considered UEP approach offers the highest spectral efficiency among the examined relaying schemes.
4.	Duong, Quang Trung, et al. (författare) Unequal Error Protection for Wireless Multimedia Transmission in Decode-and-Forward Relay Networks 2009 Konferensbidrag (refereegranskat)abstract In this paper, we propose an unequal error protection (UEP) scheme for multimedia transmission over wireless decode-and-forward (DF) relay networks. We prove that relay selection combining (R-SC) mode yields a better error rate performance than all-participate relays, i.e., distributed spacetime codes (DSTC) and orthogonal transmission with maximum ratio combining (OT-MRC) at the destination. Hence, we apply the R-SC scheme for transmitting bit sequence with high priority while the cooperative spatial multiplexing scheme is employed for the bit-stream with low priority. With this strategy, we achieve the maximum spatial diversity gain for high priority data and a high spatial multiplexing gain for low priority data. Monte- Carlo simulations and analytical results are shown to validate the proposed UEP scheme.
5.	Engelke, Ulrich, et al. (författare) An Artificial Neural Network for Quality Assessment in Wireless Imaging Based on Extraction of Structural Information 2007 Konferensbidrag (refereegranskat)abstract In digital transmission, images may undergo quality degradation due to lossy compression and error-prone channels. Efficient measurement tools are needed to quantify induced distortions and to predict their impact on perceived quality. In this paper, an artificial neural network (ANN) is proposed for perceptual image quality assessment. The quality prediction is based on structural image features such as blocking, blur, image activity, and intensity masking. Training and testing of the ANN is performed with reference to subjective experiments and the obtained mean opinion scores (MOS). It is shown that the proposed ANN is capable of predicting MOS over a wide range of image distortions. This applies to both cases, when reference information about the structure of the original image is available to the ANN but also in absence of this knowledge. The considered ANN would therefore be well suited for combination with link adaption techniques.
6.	Engelke, Ulrich, et al. (författare) Analysing Inter-Observer Saliency Variations in Task-Free Viewing of Natural Images 2010 Konferensbidrag (refereegranskat)abstract We analyse variations of saliency between human observers when viewing natural image content. For this purpose, we conducted an eye tracking experiment to record gaze patterns of humans when viewing natural images. The resulting gaze patterns were used to create saliency maps for each observer and image. A correlation analysis is then conducted with the aim to quantify the variability of saliency between the observers and the different images. The results are considered to be a first step towards gaining a better understanding regarding the reliability of saliency maps for natural images.
7.	Engelke, Ulrich, et al. (författare) Comparative Study of Fixation Density Maps 2013 Ingår i: IEEE Transactions on Image Processing. - : IEEE. - 1057-7149 .- 1941-0042. ; 22:3, s. 1121-1133 Tidskriftsartikel (refereegranskat)abstract Fixation density maps (FDM) created from eye tracking experiments are widely used in image processing applications. The FDM are assumed to be reliable ground truths of human visual attention and as such, one expects a high similarity between FDM created in different laboratories. So far, no studies have analyzed the degree of similarity between FDM from independent laboratories and the related impact on the applications. In this paper, we perform a thorough comparison of FDM from three independently conducted eye tracking experiments. We focus on the effect of presentation time and image content and evaluate the impact of the FDM differences on three applications: visual saliency modeling, image quality assessment, and image retargeting. It is shown that the FDM are very similar and that their impact on the applications is low. The individual experiment comparisons, however, are found to be significantly different, showing that inter-laboratory differences strongly depend on the experimental conditions of the laboratories. The FDM are publicly available to the research community.
8.	Engelke, Ulrich, et al. (författare) Comparing Two Eye-Tracking Databases : The Effect Of Experimental Setup And Image Presentation Time On The Creation Of Saliency Maps 2010 Konferensbidrag (refereegranskat)abstract Visual attention models are typically designed based on human gaze patterns recorded through eye tracking. In this paper, two similar eye tracking experiments from independent laboratories are presented, in which humans observed natural images under task-free condition. The resulting saliency maps are analysedwith respect to two criteria; the consistency between the experiments and the impact of the image presentation time. It is shown, that the saliency maps between the experiments are strongly correlated independent of presentation time. It is further revealed that the presentation time can be reduced without substantially sacrificing the accuracy of the convergent saliency map. The results provide valuable insight into the similarity of saliency maps from independent laboratories and are highly beneficial for the creation of converging saliency maps at reduced experimental time and cost.
9.	Engelke, Ulrich, et al. (författare) Framework for Optimal Region of Interest-based Quality Assessment in Wireless Imaging 2010 Ingår i: Journal of Electronic Imaging (JEI). - : SPIE. - 1017-9909 .- 1560-229X. ; 19:1 Tidskriftsartikel (refereegranskat)abstract Images usually exhibit regions that particularly attract the viewer's attention. These regions are typically referred to as regions-of-interest (ROI) and the underlying phenomenon in the human visual system is known as visual attention (VA). In the context of image quality one may expect that distortions occuring in the ROI are perceived as being more annoying, as compared to distortions in the background. However, VA is only seldom taken into account in existing image quality metrics. In this paper, we thus provide a VA framework to extend existing image quality metrics with a simple VA model. The performance of the framework is evaluated on three contemporary image quality metrics. We further consider the context of wireless imaging where a broad range of artifacts can be observed. To facilitate the VA based metric design, we conducted subjective experiments to both obtain a ground truth for the subjective quality of a set of test images and to identify ROI in the corresponding reference images. A methodology is further discussed to optimize the VA metrics with respect to quality prediction accuracy and generalization ability. It is shown that the quality prediction performance of the three considered metrics can be significantly improved by deploying the proposed framework.
10.	Engelke, Ulrich, et al. (författare) Human Observer Confidence in Image Quality Assessment 2012 Ingår i: Signal processing. Image communication. - : Elsevier. - 0923-5965 .- 1879-2677. ; 27:9, s. 935-947 Tidskriftsartikel (refereegranskat)abstract Mean opinion scores obtained from subjective quality assessment are widely used as a ground truth for the development of predictive quality models. The underlying variance between observer ratings is typically quantified using confidence intervals, which do not provide any direct insight into the underlying causes of the disagreement. For better understanding of human visual quality perception and to develop more accurate models, it is important to identify the factors that impact on the variations in quality ratings. This work considers one such factor: observer confidence. This consideration is motivated by the view that quality assessment is a difficult task and hence quality ratings are provided with varying levels of confidence. The first goal of this paper is to analyse the results of an experiment to determine association between observer confidence and image quality judgement. Secondly, models are developed that aim to predict mean observer confidence as a complementary measure to the widely used mean opinion scores. It is shown that there is indeed a strong interrelation between quality perception and confidence, resulting in predictive models of high accuracy.
11.	Engelke, Ulrich, et al. (författare) Linking Distortion Perception and Visual Saliency in H.264/AVC Coded Video Containing Packet Loss 2010 Konferensbidrag (refereegranskat)abstract In this paper, distortions caused by packet loss during video transmission are evaluated with respect to their perceived annoyance. In this respect, the impact of visual saliency on the level of annoyance is of particular interest, as regions and objects in a video frame are typically not of equal importance to the viewer. For this purpose, gaze patterns from a task free eye tracking experiment were utilised to identify salient regions in a number of videos. Packet loss was then introduced into the bit stream such as that the corresponding distortions appear either in a salient region or in a non-salient region. A subjective experiment was then conducted in which human observers rated the annoyance of the distortions in the videos. The outcomes show a strong tendency that distortions in a salient region are indeed perceived as much more annoying as compared to distortions in the non-salient region. The saliency of the distorted image content was further found to have a larger impact on the perceived annoyance as compared to the distortion duration. The findings of this work are considered to be of great use to improve prediction performance of video quality metrics in the context of transmission errors.
12.	Engelke, Ulrich (författare) Modelling Perceptual Quality and Visual Saliency for Image and Video Communications 2010 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The evolution of advanced radio transmission technologies for third and future generation mobile radio systems has paved the way for the delivery of mobile multimedia services. This is further enabled through contemporary video coding standards, such as H.264/AVC, allowing wireless image and video applications to become a reality on modern mobile devices. The extensive amount of data needed to represent the visual content and the scarce channel bandwidth constitute great challenges for network operators to deliver an intended quality of service. Appropriate metrics are thus instrumental for service providers to monitor the quality as experienced by the end user. This thesis focuses on subjective and objective assessment methods of perceived visual quality in image and video communication. The content of the thesis can be broadly divided into four parts. Firstly, the focus is on the development of image quality metrics that predict perceived quality degradations due to transmission errors. The metrics follow the reduced-reference approach, thus, allowing to measure quality loss during image communication with only little overhead as side information. The metrics are designed and validated using subjective quality ratings from two experiments. The distortion assessment performance is further demonstrated through an application for filter design. The second part of the thesis then investigates various methodologies to further improve the quality prediction performance of the metrics. In this respect, several properties of the human visual system are investigated and incorporated into the metric design. It is shown that the quality prediction performance can be considerably improved using these methodologies. The third part is devoted to analysing the impact of the complex distortion patterns on the overall perceived quality, following two goals. Firstly, the confidence of human observers is analysed to identify the difficulties during assessment of the distorted images, showing, that indeed the level of confidence is highly dependent on the level of visual quality. Secondly, the impact of content saliency on the perceived quality is identified using region-of-interest selections and eye tracking data from two independent subjective experiments. It is revealed, that the saliency of the distortion region indeed has an impact on the overall quality perception and also on the viewing behaviour of human observers when rating image quality. Finally, the quality perception of H.264/AVC coded video containing packet loss is analysed based on the results of a combined subjective video quality and eye tracking experiment. It is shown that the distortion location in relation to the content saliency has a tremendous impact on the overall perceived quality. Based on these findings, a framework for saliency aware video quality assessment is proposed that strongly improves the quality prediction performance of existing video quality metrics.
13.	Engelke, Ulrich, et al. (författare) Modelling Saliency Awareness for Objective Video Quality Assessment 2010 Konferensbidrag (refereegranskat)abstract Existing video quality metrics do usually not take into consideration that spatial regions in video frames are of varying saliency and thus, differently attract the viewer's attention. This paper proposes a model of saliency awareness to complement existing video quality metrics, with the aim to improve the agreement of objectively predicted quality with subjectively rated quality. For this purpose, we conducted a subjective experiment in which human observers rated the annoyance of videos with transmission distortions appearing either in a salient region or in a non-salient region. The mean opinion scores confirm that distortions in salient regions are perceived much more annoying. It is shown that application of the saliency awareness model to two video quality metrics considerably improves their quality prediction performance.
14.	Engelke, Ulrich, et al. (författare) Multi-resolution Structural Degradation Metrics for Perceptual Image Quality Assessment 2007 Konferensbidrag (refereegranskat)abstract In this paper, a multi-resolution analysis is proposed for image quality assessment. Structural features are extracted from each level of a pyramid decomposition that accurately represents the multiple scales of processing in the human visual system. To obtain an overall quality measure the individual level metrics are accumulated over the considered pyramid levels. Two different metric design approaches are introduced and evaluated. It turns out that one of them outperforms our previous work on single-resolution image quality assessment.
15.	Engelke, Ulrich, et al. (författare) Multiobjective Optimization of Multiple Scale Visual Quality Processing 2008 Konferensbidrag (refereegranskat)abstract In this paper, multiobjective optimization is applied to determine the optimal feature weights for a multi-resolution image quality metric. The optimization is conducted with respect to two aims; maximization of quality prediction accuracy and generalisation ability to unknown images. A thresholding of the optimal weights is applied to further reduce computational complexity of the quality metric. A detailed discussion of the tradeoff between prediction performance and complexity with respect to the threshold is provided. The metric design and evaluation is supported using mean opinion scores from subjective quality experiments that we conducted in two independent laboratories. Comparison to other state of the art quality metrics reveals the ability of the proposed metric to accurately predict subjective image quality perception.
16.	Engelke, Ulrich, et al. (författare) On Confidence and Response Times of Human Observers in Subjective Image Quality Assessment 2009 Konferensbidrag (refereegranskat)abstract Mean opinion scores obtained in subjective image quality experiments are widely accepted as measures of perceived visual quality. They have, however, a strong limitation regarding the reliability of the rated quality, since there is no explicit information as to whether the human observer experienced difficulties when judging image quality. We thus suggest that additional information about the observers confidence should be provided along with the actual quality measure. In this paper, we analyse two ways of obtaining this confidence measure; firstly as a confidence score given by the human observer and secondly as an indirect measure of the observers response time to provide the quality score. We reveal strong relationships of confidence scores and response times to the quality scores. We further propose a model to predict observer confidence based on the quality scores and response times.
17.	Engelke, Ulrich, et al. (författare) On Perceptual Quality Evaluation of Video Applications for Wireless Ad-hoc Networks 2007 Konferensbidrag (refereegranskat)
18.	Engelke, Ulrich, et al. (författare) Optimal Region-of-Interest Based Visual Quality Assessment 2009 Konferensbidrag (refereegranskat)abstract Visual content typically exhibits regions that particularly attract the viewer's attention, usually referred to as regions-of-interest (ROI). In the context of visual quality one may expect that distortions occurring in the ROI are perceived more annoyingly than distortions in the background (BG). This is especially true given that the human visual system is highly space variant in sampling visual signals. However, this phenomenon of visual attention is only seldom taken into account in visual quality metric design. In this paper, we thus provide a framework for incorporation of visual attention into the design of an objective quality metric by means of region-based segmentation of the image. To support the metric design we conducted subjective experiments to both quantify the subjective quality of a set of distorted images and also to identify ROI in a set of reference images. Multiobjective optimization is then applied to find the optimal weighting of the ROI and BG quality metrics. It is shown that the ROI based metric design allows to increase quality prediction performance of the considered metric and also of two other contemporary quality metrics.
19.	Engelke, Ulrich, et al. (författare) Pareto Optimal Weighting of Structural Impairments for Wireless Imaging Quality Assessment 2008 Konferensbidrag (refereegranskat)abstract In this paper, we consider multiobjective optimization for obtaining the feature weights associated with structural image impairments and its application to wireless imaging quality assessment. The proposed framework supports optimization with respect to finding a trade-off between metric prediction accuracy and generalization to unknown images. Evaluation of optimal trade-off solutions for two representative scenarios reveal the benefits of the proposed approach. In particular, quality prediction accuracy of an objective image metric can be strongly increased and negligible features are identified that can be discarded to save computational complexity.
20.	Engelke, Ulrich, et al. (författare) Perceptual-based Quality Metrics for Image and Video Services : A Survey 2007 Konferensbidrag (refereegranskat)abstract The accurate prediction of quality from an end-user perspective has received increased attention with the growing demand for compression and communication of digital image and video services over wired and wireless networks. The existing quality assessment methods and metrics have a vast reach from computational and memory efficient numerical methods to highly complex models incorporating aspects of the human visual system. It is hence crucial to classify these methods in order to find the favorable approach for an intended application. In this paper a survey and classification of contemporary image and video quality metrics is therefore presented along with the favorable quality assessment methodologies. Emphasis is given to those metrics that can be related to the quality as perceived by the end-user. As such, these perceptual-based image and video quality metrics may build a bridge between the assessment of quality as experienced by the end-user and the quality of service parameters that are usually deployed to quantify service integrity.
21.	Engelke, Ulrich, et al. (författare) Perceptual Evaluation of Motion JPEG2000 Quality over Wireless Channels 2006 Konferensbidrag (refereegranskat)abstract In this paper, we investigate the applicability of perceptual image quality metrics for quality assessment of Motion JPEG2000 (MJ2) video streams over wireless channels. A performance evaluation of MJ2 quality for different levels of source compression and channel coding settings is provided. This reveals insights into the characteristics and suitability of the considered perceptual quality metrics for wireless video quality assessment. In particular, a reduced-reference hybrid image quality metric (HIQM) is identified as the most favorable metric with respect to supporting real-time applications. The findings obtained from the considered scenarios may also guide the design of efficient physical layer functions for wireless video systems.
22.	Engelke, Ulrich, et al. (författare) Perceptual Quality Assessment of Wireless Video Applications 2006 Konferensbidrag (refereegranskat)abstract The rapid evolution of wireless networks is driven by the growth of wireless packet data applications such as interactive mobile multimedia applications, wireless streaming services, and video-on-demand. The largely heterogeneous network structures, severe channel impairments, and complex traffic patterns make the wireless networks much more unpredictable compared to their wired counterparts. One of the major challenges with the roll-out of these services is therefore the design of wireless networks that fulfill the stringent quality of service requirements of wireless video applications. In this paper, the applicability of perceptual image quality metrics for real-time quality assessment of Motion JPEG2000 (MJ2) video streams over wireless channels is investigated. In particular, a reduced-reference hybrid image quality metric (HIQM) is identified as suitable for an extension to video applications. It outperforms other known metrics in terms of required overhead and prediction performance.
23.	Engelke, Ulrich, et al. (författare) Perceptual Quality Measures for Image and Video Services 2006 Annan publikation (övrigt vetenskapligt/konstnärligt)
24.	Engelke, Ulrich (författare) Perceptual Quality Metric Design for Wireless Image and Video Communication 2008 Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract The evolution of advanced radio transmission technologies for third generation mobile radio systems has paved the way for the delivery of mobile multimedia services. In particular, wireless image and video applications are among the most popular services offered on modern mobile devices to support communication beyond the traditional voice services. The large amount of data necessary to represent the visual content and the scarce bandwidth of the wireless channel impose new challenges for the network operator to deliver high quality image and video services. Link layer metrics have conventionally been used to monitor the received signal quality but were found to not accurately reflect the visual quality as it is perceived by the end-user. These metrics thus need to be replaced by suitable metrics that measure the overall impairments induced during image or video communication and accurately relate them to subjectively perceived quality. In this thesis, we focus on objective metrics that are able to quantify the end-to-end visual quality in wireless image and video communication. Such metrics may then be utilised to support the efficient use of link adaptation and resource management techniques and thus guarantee a certain quality of service to the user. The thesis is divided into four parts. The first part contributes an extensive survey and classification of contemporary image and video quality metrics that may be applicable in a communication context. The second part then discusses the development of the Normalised Hybrid Image Quality Metric (NHIQM) that we propose for prediction of visual quality degradations induced during wireless communication. The metric is based on a set of structural features, which are deployed to quantify artifacts that may occur in a wireless communication system and also are well aligned to characteristics of the human visual system (HVS). In the third part, three metric designs are discussed that utilise the same structural feature set as a basis for quality prediction. Incorporation of further HVS characteristics into the metric design will then improve even more the visual quality prediction performance. The design and validation of all proposed metrics is supported by subjective quality experiments that we conducted in two independent laboratories. Comparison to other state of the art visual quality metrics reveals the ability of the proposed metrics to accurately predict visual quality in a wireless communication system. The last part contributes an application of NHIQM for filter design. In particular, the filtering performance of a de-blocking de-ringing post filter for H.263 video sequences is analysed with regards to visual quality of the filtered sequence when applying appropriate filter parameter combinations.
25.	Engelke, Ulrich, et al. (författare) Psychophysical Assessment of Perceived Interest in Natural Images : The ROI-D Database 2011 Konferensbidrag (refereegranskat)abstract We introduce a novel region-of-interest (ROI) database for natural image content, the ROI-D database. The database consists of ROI maps created from manual selections obtained in a psychophysical experiment with 20 participants. The presented stimuli were 42 photographic images taken from 3 publicly available image quality databases. In addition to the ROI selections, dominance ratings were recorded that provide further insight into the interest of the selected ROI in relation to the background. In this paper, the experiment is described, the resulting ROI database is analysed, and possible applications of the database are discussed. The ROI-D database is made freely available to the image processing research community.
26.	Engelke, Ulrich, et al. (författare) Psychophysiology-Based QoE Assessment : A Survey 2017 Ingår i: IEEE Journal on Selected Topics in Signal Processing. - 1932-4553 .- 1941-0484. ; 11:1, s. 6-21 Tidskriftsartikel (refereegranskat)abstract We present a survey of psychophysiology-based assessment for quality of experience (QoE) in advanced multimedia technologies. We provide a classification of methods relevant to QoE and describe related psychological processes, experimental design considerations, and signal analysis techniques. We summarize multimodal techniques and discuss several important aspects of psychophysiology-based QoE assessment, including the synergies with psychophysical assessment and the need for standardized experimental design. This survey is not considered to be exhaustive but serves as a guideline for those interested to further explore this emerging field of research.
27.	Engelke, Ulrich, et al. (författare) Quality Assessment of an Adaptive Filter for Artifact Reduction in Mobile Video Sequences 2007 Konferensbidrag (refereegranskat)abstract In this paper, we examine an adaptive deblocking deringing filter for mobile video sequences in H.263 format. The considered filter has been designed with reference to the constraints of computational complexity and working memory of mobile terminals. The post filter suggested by the International Telecommunications Union (ITU) in Recommendation H.263 App. III is also included as a reference. Given that fidelity metrics such as the peak signal-to-noise ratio (PSNR) do not necessarily correlate well with video quality as experienced by the user, we consider in this paper objective quality metrics that can incorporate knowledge about the user's perception into the quality assessment. Guidelines for choosing filter parameters in relation to user-perceived video quality are obtained from the numerical results.
28.	Engelke, Ulrich, et al. (författare) Quality Evaluation in Wireless Imaging Using Feature-Based Objective Metrics 2007 Konferensbidrag (refereegranskat)abstract This paper addresses the evaluation of image quality in the context of wireless systems using feature-based objective metrics. The considered metrics comprise of a weighted combination of feature values that are used to quantify the extend by which the related artifacts are present in a processed image. In view of imaging applications in mobile radio and wireless communication systems, reduced-reference objective quality metrics are investigated for quantifying user-perceived quality. The examined feature-based objective metrics provide options for controlling the processing complexity and implementation resources required for performing the quality evaluation. Furthermore, the metrics support the scaling of overhead needed for communicating the image features over the wireless link and the accuracy for predicting the image quality.
29.	Engelke, Ulrich, et al. (författare) Quality of Experience of Multimedia Services : Past, Present, and Future 2011 Konferensbidrag (refereegranskat)abstract In recent years, the notion of Quality of Experience (QoE) has gained increased attention to represent the quality of a service as it is perceived by the users. Accordingly, QoE amalgamates service integrity quantified by conventional\linebreak Quality of Service (QoS) parameters with non-technical but subjective factors. In this paper, we provide a survey on the evolution of QoE concepts in multimedia systems touching on the past, present, and future aspects. Specifically, the ideas behind QoE are discussed and an overview of related standardization work is provided. On this basis, QoE metrics for speech, image, and video are described. An outlook of future work and challenges is also provided.
30.	Engelke, Ulrich, et al. (författare) Reduced-reference metric design for objective perceptual quality assessment in wireless imaging 2009 Ingår i: Signal Processing-Image Communication. - : ELSEVIER. - 0923-5965. ; 24:7, s. 525-547 Tidskriftsartikel (refereegranskat)abstract The rapid growth of third and development of future generation mobile systems has led to an increase in the demand for image and video services. However, the hostile nature of the wireless channel makes the deployment of such services much more challenging, as in the case of a wireline system. In this context, the importance of taking care of user satisfaction with service provisioning as a whole has been recognized. The related user-oriented quality concepts cover end-to-end quality of service and subjective factors such as experiences with the service. To monitor quality and adapt system resources, performance indicators that represent service integrity have to be selected and related to objective measures that correlate well with the quality as perceived by humans. Such objective perceptual quality metrics can then be utilized to optimize quality perception associated with applications in technical systems. In this paper, we focus on the design of reduced-reference objective perceptual image quality metrics for use in wireless imaging. Specifically, the Normalized Hybrid Image Quality Metric (NHIQM) and a perceptual relevance weighted L_p-norm are designed. The main idea behind both feature-based metrics relates to the fact that the human visual system (HVS) is trained to extract structural information from the viewing area. Accordingly, NHIQM and L_p-norm are designed to account for different structural artifacts that have been observed in our distortion model of a wireless link. The extent by which individual artifacts are present in a given image is obtained by measuring related image features. The overall quality measure is then computed as a weighting sum of the features with the respective perceptual relevance weight obtained from subjective experiments. The proposed metrics differ mainly in the pooling of the features and amount of reduced-reference produced. While NHIQM performs the pooling at the transmitter of the system to produce a single value as reduced-reference, the L_p-norm requires all involved feature values from the transmitted and received image to perform the pooling on the feature differences at the receiver. In addition, non-linear mapping functions are developed that relate the metric values to predicted mean opinion scores (MOS) and account for saturations in the HVS. The evaluation of prediction performance of NHIQM and the L_p-norm reveals their excellent correlation with human perception in terms of accuracy, monotonicity, and consistency. This holds not only for the prediction performance on images taken for the training of the metrics but also for the generalization to unknown images. In addition, it is shown that the NHIQM approach and the perceptual relevance weighted L_p-norm outperform other prominent objective quality metrics in prediction performance.
31.	Engelke, Ulrich, et al. (författare) Regional Attention to Structural Degradations for Perceptual Image Quality Metric Design 2008 Konferensbidrag (refereegranskat)abstract In this paper, regional attention to structural degradations in images is analyzed to improve perceptual quality prediction performance of objective image quality metrics. Subjective experiments were conducted to identify regions-of-interest for a set of natural images. A region-selective metric design is then applied to four objective image quality metrics which were trained and validated with respect to quality prediction accuracy and generalization to unknown images. For this purpose, data is used from subjective quality experiments conducted at two independent laboratories. It is shown that the region-selective design is highly beneficial for the considered objective image quality metrics, in particular, prediction accuracy can be significantly increased.
32.	Engelke, Ulrich, et al. (författare) Subjective Quality Assessment for Wireless Image Communication : The Wireless Imaging Quality Database 2010 Konferensbidrag (refereegranskat)abstract Mean opinion scores (MOS) obtained in image quality experiments are a key component in the transition from subjective to objective measures of perceived quality. In this respect, MOS are widely used to validate objective quality prediction models. To facilitate comparison between models from different laboratories it is desirable to have publicly available image quality databases. Several databases were made available in recent years. In this paper, we introduce the Wireless Imaging Quality (WIQ) database which, unlike any of the previous databases, takes into account the complex nature of a wireless communications link. The database is thus considered as a valuable complement to the existing databases. The distortion model, the test images, and two quality experiments that we conducted are explained in this paper. A number of contemporary objective quality metrics are tested for their quality prediction performance on the database. The WIQ database including test images and MOS is made freely available to the research community.
33.	Engelke, Ulrich, et al. (författare) The Effect of Spatial Distortion Distributions on Human Viewing Behaviour when Judging Image Quality 2009 Konferensbidrag (refereegranskat)abstract In wireless communication, distortions are induced into an image through both lossy source coding and an error prone channel. The combination thereof causes complex distortion patterns in the visual content which vary strongly in their spatial distribution, some being uniformly spread and others being locally clustered. In the context of image quality, it is of interest to identify as to how the distribution of the distortions impact on the visual attention of human observers and thus on the perceived quality. For this reason, we conducted an experiment in which fifteen participants were asked to rate the quality of eighty distorted images and their corresponding reference images, while we recorded their gaze patterns using an eye tracker. The test images contained a wide range of artifact magnitudes, both locally and globally distributed, and were created using a wireless channel simulation model. We then correlate the visual gaze patterns of the human observers with local energy measures of the distortions in order to identify the effect of distortion distributions on the viewing behaviour of human observers when judging image quality. The outcomes serve to improve the prediction performance of objective image quality metrics that we previously proposed.
34.	Engelke, Ulrich, et al. (författare) Visual Attention in Quality Assessment 2011 Ingår i: IEEE signal processing magazine (Print). - : IEEE. - 1053-5888 .- 1558-0792. ; 28:6, s. 50-59 Tidskriftsartikel (refereegranskat)abstract Perceptual quality metrics are widely deployed in image and video processing systems. These metrics aim to emulate the integral mechanisms of the human visual system (HVS) to correlate well with visual perception of quality. One integral property of the HVS is, however, often neglected: visual attention (VA) [1]. The essential mechanisms associated with VA consist mainly of higher cognitive processing, deployed to reduce the complexity of scene analysis. For this purpose, a subset of the visual information is selected by shifting the focus of attention across the visual scene to the most relevant objects. By neglecting VA, perceptual quality models inherently assume that all objects draw the attention of the viewer to the same degree.
35.	Engelke, Ulrich, et al. (författare) Visual Attention Modeling : Region-of-Interest Versus Fixation Patterns 2009 Konferensbidrag (refereegranskat)abstract Visual attention (VA) is an integral property of the human visual system. The deployment of a VA model can be beneficial for many image and video applications, such as, compression, transmission, and quality assessment. However, the design of a VA model is highly dependent on the subjective VA data used as ground truth and the application that the model is intended for. In this paper, we discuss two ways of obtaining subjective VA data that can subsequently be used to develop VA models; selective regions-of-interest and visual fixation patterns. The feasibility of both methods will be discussed, in particular, with respect to visual quality assessment.
36.	Engelke, Ulrich, et al. (författare) Visual Attention Modelling for Subjective Image Quality Databases 2009 Konferensbidrag (refereegranskat)abstract The modelling of perceptual image quality metrics has experienced increased effort in recent years. In order to allow for model design, validation, and comparison, a number of subjective image quality databases has been made available to the research community. Most metrics that were designed using these databases assess the quality uniformly over the whole image, not taking into account stronger attention to salient regions of an image. In order to facilitate incorporation of visual attention (VA) into objective metric design we have conducted an eye tracking experiment. The experiment and its outcomes will be explained in detail in this paper. The actual gaze data recorded in the experiment is publicly available in order to facilitate and encourage VA modelling for image quality metrics.
37.	Engelke, Ulrich, et al. (författare) Visual Fixation Patterns in Subjective Quality Assessment : The Relative Impact of Image Content and Structural Distortions 2010 Konferensbidrag (refereegranskat)abstract The viewing behaviour of human observers during image quality assessment is analysed. In this respect, the relative impact of image content and structural distortions is of particular interest. Two subjective experiments were conducted as a basis for analysis; a region-of-interest (ROI) experiment and an eye tracking experiment under quality assessment task. A correlation analysis and a receiver operating characteristics analysis reveal, that quality assessment takes place mainly within the ROI, indicating a higher impact of the content as compared to the distortions. This seems to be only contradicted by very strong and localised distortions outside the ROI.
38.	Iqbal, Muhammad Imran, et al. (författare) Error Sensitivity Analysis for Wireless JPEG2000 Using Perceptual Quality Metrics 2008 Konferensbidrag (refereegranskat)abstract Quality assessment of mobile and wireless multimedia services including image and video applications has gained increased attention in recent years as a means of facilitating efficient radio resource management. In particular, approaches that utilize perceptual-based metrics are becoming more dominant, as conventional fidelity metrics such as the peak signal-to-noise ratio (PSNR) may not correlate well with quality as perceived by the human observer. In this paper, we focus on the error sensitivity analysis for images given in the wireless JPEG2000 (JPWL) format using perceptual quality metrics. Specifically, the perceptual quality improvements obtained by progressively decoding an increasing number of image packets are examined. It is shown that the considered perceptual quality metrics exploiting structural image features may accompany or replace the PSNR-based error sensitivity description (ESD) marker segment in the wireless JPEG2000 standard. This addition will increase the effectiveness of the ESD marker segment as it facilitates the communication of reduced-reference information about the image quality from the transmitter to the receiver. In addition, the proposed approach can be used to guide the design of preferential error control coding schemes, link adaptation techniques, and selective retransmission of packets with respect to their contribution to overall quality as perceived by humans.
39.	Iqbal, Muhammad Imran, et al. (författare) Perceptual-based quality assessment of error protection schemes for wireless JPEG2000 2009 Konferensbidrag (refereegranskat)abstract Designing wireless imaging services with acceptable quality imposes great challenges due to the severe impairments induced by wireless channels, high data rate demands and limited transmission bandwidth. In this paper, we examine different error protection schemes for the JPEG2000 codestream using the error control codes offered by the wireless JPEG2000 (JPWL) standard. In particular, two unequal error protection (UEP) schemes are considered. In the first scheme, only the initial and more important packets of the JPWL codestream are protected while the remaining packets are left without protection. In contrast, the second scheme uses a strong code for the initial packets while a weaker code is used for the tail packets. As quality of visual services may not be captured adequately with traditional link layer metrics, code selection and their performance assessment is based on perceptual quality metrics. Specifically, the LP -norm, structural similarity (SSIM) index and visual information fidelity (VIF) criterion are utilized. Numerical results are provided for a range of system conditions under which UEP outperforms conventional equal error protection in terms of perceptual quality metrics.
40.	Zepernick, Hans-Juergen, et al. (författare) On the Impact of COVID-19 on Subjective Digital Media Quality Assessment 2021 Ingår i: IEEE 23rd International Workshop on Multimedia Signal Processing, MMSP 2021. - : Institute of Electrical and Electronics Engineers Inc.. - 9781665432870 Konferensbidrag (refereegranskat)abstract The COVID-19 pandemic has induced dramatic effects in all areas of society worldwide. It has led to drastic restrictions on academic exchanges and caused research projects to be put on hold. The need to maintain social distancing has severely affected the research communities that rely on in-person studies. In particular, Quality of Experience (QoE) research relies heavily on user studies and in-person subjective tests as means of obtaining ground truths for system designs. In this position paper, we focus on the impact of COVID-19 on conducting subjective tests for digital media quality assessment. An overview of the related discussions that take place in associated research communities is provided. A number of challenges are posed in terms of hygiene, ethics, standardization, and research quality issues. Opportunities for consolidating QoE research under COVID-19 and beyond are put forward, including alternative experimental designs and adaptation of research methodologies. Numerous enablers are suggested and discussed, revealing various avenues that can be followed to assist in conducting subjective tests under pandemic conditions. We believe that this position paper will be helpful for researchers and practitioners relying on in-person studies to keep abreast about the potential measures that support coming out of the COVID-19 pandemic strong and being prepared for future endeavors. © 2021 IEEE.

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