| 51. |
- Duong, Quang Trung, et al.
(författare)
-
End-to-End Performance of Randomized Distributed Space-Time Codes
- 2010
-
Konferensbidrag (refereegranskat)abstract
- The exact closed-form expressions for symbol error probability and outage probability of randomized distributed space-time codes (RDSTC) under Rayleigh fading are derived. The diversity gain derived in the literature uses the Chernoff bound which may not be achievable in general. Utilizing the exact expression, the achievable diversity gain of RDSTCs is validated. The closed-form expressions are verified by Monte-Carlo simulations.
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| 52. |
- Duong, Quang Trung, et al.
(författare)
-
Exact Average Symbol Error Rate of Cooperative Spatial Multiplexing in Composite Channels
- 2008
-
Konferensbidrag (refereegranskat)abstract
- Performance of cooperative spatial multiplexing systems over composite channels is presented. In particular, we derive the exact closed-form average symbol error rate (SER) expressions for cooperative spatial multiplexing systems with linear equalization receiver (e.g., Zero-Forcing) and M-ary modulation scheme in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the average SER is expressed in the forms of Appell hypergeometric function. Applying the series representation of Appell hypergeometric function, we derive a very tight approximation for the average SER. We also perform Monte-Carlo simulations to validate our analysis.
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| 53. |
- Duong, Quang Trung, et al.
(författare)
-
Exact outage probability of cognitive AF relaying with underlay spectrum sharing
- 2011
-
Ingår i: Electronics Letters. - : Institution of Engineering and Technology -IET. - 0013-5194 .- 1350-911X. ; 47:17, s. 1001-1002
-
Tidskriftsartikel (refereegranskat)abstract
- The exact closed-form expression for the outage probability (OP) of cognitive radio dual-hop amplify-and-forward (AF) relay networks is derived. The tractable expression of the OP, given in the form of elementary functions, readily enables evaluating the effect of primary users on the secondary system performance. It has been shown that the use of AF relaying significantly improves the performance of cognitive radio networks compared to its direct transmission counterpart.
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| 54. |
- Duong, Quang Trung, et al.
(författare)
-
Hybrid Decode-Amplify-Forward Cooperative Communications with Multiple Relays
- 2009
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the performance gain of hybrid decode-amplify-forward (HDAF) relay protocol over the two conventional ones: the adaptive decode-forward (ADF) and amplify-forward (AF) in dual-hop multiple-relay networks. We analyze the performance gain in terms of the symbol error probability (SEP) in the high signal-to-noise ratio (SNR) regime. Similarly as in the single relay case [1], under a specific modulation scheme, these gains only depend on the ratio of channel mean power between the first-hop and second-hop transmission. In particular, we show that the HDAF protocol obtains a large gain, medium gain, and small gain over ADF, AF as the relays are placed close to the destination, half-way between the source and destination (symmetric case), and nearby the source, respectively. In contrast to the single-relay case in which the HDAF scheme has no benefit compared to ADF and AF as the relay is located close to the source [1], HDAF still achieves a small gain with multiple relays. Interestingly, we further show that for all cases the performance gains are saturated as the number of relays is large.
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| 55. |
- Duong, Quang Trung, et al.
(författare)
-
Keyhole Effect in Dual-Hop MIMO AF Relay Transmission with Space-Time Block Codes
- 2012
-
Ingår i: IEEE Transactions on Communications. - : IEEE. - 0090-6778 .- 1558-0857. ; 60:12, s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the effect of keyhole on the performance of multiple-input multiple-output (MIMO) amplifyand-forward (AF) relay networks with orthogonal space-time block codes (OSTBCs) transmission is investigated. In particular, we analyze the asymptotic symbol error probability (SEP) performance of a downlink communication system where the amplifying processing at the relay can be implemented by either the linear or squaring approach. Our tractable asymptotic SEP expressions enable us to obtain both diversity and array gains. Our finding reveals that with condition nS > min(nR, nD), the linear approach can provide the full achievable diversity gain of min(nR, nD) when only the second hop suffers from the keyhole effect, i.e., single keyhole effect (SKE), where nS, nR, and nD are the number of antennas at source, relay, and destination, respectively. However, for the case that both the source-relay and relay-destination links experience the keyhole effect, i.e., double keyhole effect (DKE), the achievable diversity order is only one regardless of the number of antennas. In contrast, utilizing the squaring approach, the overall diversity gain can be achieved as min(nR, nD) for both SKE and DKE. An important observation corroborated by our studies is that for satisfying the tradeoff between performance and complexity, we should use the linear approach for SKE and the squaring approach for DKE.
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| 56. |
- Duong, Quang Trung, et al.
(författare)
-
Multi-Keyhole Effect in MIMO AF Relay Downlink Transmission with Space-Time Block Codes
- 2011
-
Konferensbidrag (refereegranskat)abstract
- Multi-keyhole bridges the gap between single keyhole and full-scattering multiple-input multiple-output (MIMO) channels. In this paper, we therefore investigate the multi-keyhole effect on the MIMO amplify-and-forward (AF) relay downlink transmission with orthogonal space-time block codes. In particular, we derive the analytical symbol error rate (SER) expression for the considered system with arbitrary number of keyholes. Moreover, SER approximations in the high SNR regime for several important special scenarios of multi-keyhole channels are further derived. These asymptotic results provide important insights into the impact of system's parameters on the SER performance. Our analysis is confirmed by comparing with Monte-Carlo simulations.
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| 57. |
- Duong, Quang Trung, et al.
(författare)
-
On the Ergodic Capacity of Cooperative Spatial Multiplexing Systems in Composite Channels
- 2009
-
Konferensbidrag (refereegranskat)abstract
- The ergodic capacity of cooperative spatial multiplexing systems over composite channels is presented. Specifically, we derive the exact closed-form expressions for ergodic capacity of cooperative spatial multiplexing systems with linear receiver in the composite channel of log-normal shadowing and Rayleigh fading. Using the Gauss-Hermite quadrature integration, the final analytical result of ergodic capacity is described in a closed-form expression. We also perform Monte-Carlo simulations to validate our analysis. Subsequently, we apply the obtained analytical expression to evaluate some representative scenarios regarding to spatial multiplexing gain in relay composite channels
|
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| 58. |
- Duong, Quang Trung, et al.
(författare)
-
On the Performance Gain of Hybrid Decode-Amplify-Forward Cooperative Communications
- 2009
-
Ingår i: EURASIP Journal on Wireless Communications and Networking. - : Hindawi Publishing Corporation. - 1687-1472 .- 1687-1499. ; 2009
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the performance of adaptive decode-forward (ADF), amplify-forward (AF), and hybrid decode-amplify-forward (HDAF) relaying protocol. In particular, we derive the closedform expression of symbol error probability (SEP) for these three relaying protocols. For the AF protocol, we derive a simpler and more tractable final result than previously published work [1]. Furthermore, analyzing the high signal-to-noise ratio (SNR) regime, we derive an asymptotically tight approximation for SEP. Especially, for the AF protocol, our SEP approximation is tighter than the result in [2]. The SEP approximation is used to assess an important aspect between the three different relaying protocols, i.e., the SEP performance gain of HADF over the two conventional relaying schemes ADF and AF. It is shown that the performance gain of HDAF over ADF and AF significantly depends on the relative value of channel conditions between source-to-relay and relay-to- estination link (relay channels). Interestingly, it is shown that the HDAF protocol has no benefit compare to the two others if the relay is located close to the source. In contrast, the performance gains of HDAF over the ADF and AF scheme are remarkably large as the relay moves nearby the destination. Specifically, the numerical results given as well as our analysis indicate that for QPSK modulation, HDAF outperforms ADF and AF with a performance improvement by 5 dB and 6 dB, respectively.
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| 59. |
- Duong, Quang Trung, et al.
(författare)
-
On the Performance of ROI-Based Image Transmission Using Cooperative Diversity
- 2008
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we examine the spatial diversity of cooperative communications for image transmission without deploying multiple antennas at the transmitter. We propose a novel region of interest (ROI)-based scheme for image transmission over wireless cooperative/relay fading channels. By having the relay terminal assist the direct communications, we can increase the resilience for ROI against the error-prone fading channels. Our proposed scheme significantly improves the performance of ROI compared to the direct communications (no-cooperation) and conventional relay networks without performing any forward error correction. Although we focus on the adaptive decode-forward (ADF) relay protocol, our proposed scheme can be easily adopted to any other relaying protocol such as fixed decode-forward (FDF), amplify-forward (AF), hybrid decode-amplify-forward (HDAF), and distributed-Alamouti space--time coding. Simulation results show that under the the same total transmit power constraint our proposed scheme significant outperforms the conventional ones in terms of bit error rate (BER) and peak signal-to-noise ratio (PSNR).
|
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| 60. |
- Duong, Quang Trung, et al.
(författare)
-
On the Performance of Selection Decode-and-Forward Relay Networks over Nakagami-m Fading Channels
- 2009
-
Ingår i: IEEE Communications Letters. - 1089-7798 .- 1558-2558. ; 13:3, s. 172-174
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the performance of fixed decode-and-forward cooperative networks with relay selection over independent but not identically distributed Nakagamim fading channels, with integer values of the fading severity parameter m. Specifically, closed-form expressions for the symbol error probability and the outage probability are derived using the statistical characteristic of the signal-to-noise ratio. We also perform Monte-Carlo simulations to verify the analytical results
|
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| 61. |
- Duong, Quang Trung, et al.
(författare)
-
Opportunistic relaying for cognitive network with multiple primary users over Nakagami-m fading
- 2013
-
Konferensbidrag (refereegranskat)abstract
- The performance of cognitive spectrum sharing systems with opportunistic relay selection over Nakagami-m fading is analyzed in the presence of multiple primary users (PUs). In particular, we derive an exact closed-form expression for the outage probability (OP) of the considered cognitive relay systems under the joint impact of maximal transmit power Pt at secondary transmitter and peak interference power Ip at the primary user. Our general formulas cover several specific practical scenarios, e.g., where the maximal transmit power can be neglected compared to the peak interference power. In addition, a tractable expression for the asymptotic OP is also derived and reveals important insights into the system performance. We show that the number of PUs only affects the coding gain but not the diversity gain.
|
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| 62. |
- Duong, Quang Trung, et al.
(författare)
-
Orthogonal Space-Time Block Codes with CSI-Assisted Amplify-and-Forward Relaying in Correlated Nakagami-m Fading Channels
- 2011
-
Ingår i: IEEE Transactions on Vehicular Technology. - : IEEE. - 0018-9545 .- 1939-9359. ; 60:3, s. 882-889
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the performance of multiple-input multiple-output (MIMO) dual-hop amplify-and-forward (AF) relay systems using orthogonal space-time block codes (OSTBCs) over arbitrarily correlated Nakagami-m fading channels is analyzed. In particular, closed-form expressions for the end-to-end outage probability (OP) and the symbol error probability (SEP) with arbitrary number of transceiver antennas and general correlation matrices are derived. Their mathematically tractable forms readily enable us to evaluate the performance of MIMO AF relay systems that utilize OSTBCs. For sufficiently high signal-to-noise ratios, asymptotically tight approximations for the OP and SEP are also attained which reveal insights into the effects of fading parameters and antenna correlation on the system’s performance. Furthermore, we prove that the correlation has no impact on the achievable diversity gain which is equal to the minimum of the sum of fading parameters between the two hops. Selected numerically evaluated results are presented showing an excellent agreement between the proposed analysis and equivalent Monte-Carlo simulations.
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| 63. |
- Duong, Quang Trung, et al.
(författare)
-
OSTBC Transmission in MIMO AF Relay Systems with Keyhole and Spatial Correlation Effects
- 2011
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the degenerative effects of antenna correlation and keyhole on the performance of multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay networks. In particular, we considered a downlink MIMO AF relay system consisting of an nS-antenna base station S, an nR-antenna relay station R, and an nD-antenna mobile station D, in which the signal propagation originated from the mobile station suffers from keyhole and spatial correlation effects. We have derived an exact expression for the moment generation function of the instantaneous signal-to-noise ratio which enables us to analyze the symbol error probability and outage probability of the considered system.We have shown that although the mobile station is in a poor scattering environment, i.e., keyhole, the relay channel (S → R → D link) still achieves a cooperative diversity order of min(nR, nD) provided that the channel from the source (S → R link) is keyhole-free. This result is important to radio system designers since under such a severe scenario it is unnecessary to deploy a large number of antennas on the relay station (nR) but only requires nR = nD to obtain the maximum achievable diversity gain.
|
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| 64. |
- Duong, Quang Trung, et al.
(författare)
-
Outage probability of MIMO AF relay networks over Nakagami-m fading channels
- 2010
-
Ingår i: Electronics Letters. - : The Institution of Engineering and Technology. - 0013-5194 .- 1350-911X. ; 46:17
-
Tidskriftsartikel (refereegranskat)abstract
- The outage probability (OP) of multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay networks using orthogonal space-time block code is investigated. In particular, a closed-form tight lower bound expression for the OP over independently but not necessarily identically distributed Nakagami-m fading channels is derived. Moreover, an asymptotic approximation for OP which reveals the coding and diversity gains is presented. The analytical expressions are validated by Monte-Carlo simulations.
|
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| 65. |
- Duong, Quang Trung, et al.
(författare)
-
Performance Analysis of Amplify-and-Forward MIMO Relay Networks with Transmit Antenna Selection over Nakagami-m Channels
- 2010
-
Konferensbidrag (refereegranskat)abstract
- We analyze the performance of amplify-and-forward (AF) multiple-input multiple-output (MIMO) cooperative networks over independent but not identically distributed Nakagami-$m$ fading channels. Specifically, we consider an AF MIMO relay network where the source deploys the transmit antenna selection scheme to communicate with the destination through the help of a relay. We derive closed-form approximations for outage probability (OP) and symbol error probability (SEP). Moreover, asymptotically tight approximations for OP and SEP have been obtained to facilitate insights on how fading parameters affect the performance. Our analytical results are verified by Monte-Carlo simulations for respective scenarios.
|
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| 66. |
- Duong, Quang Trung, et al.
(författare)
-
Performance Analysis of Cooperative Spatial Multiplexing with Amplify-and-Forward Relays
- 2009
-
Konferensbidrag (refereegranskat)abstract
- Cooperative spatial multiplexing (CSM) systems can achieve high spatial multiplexing gain in wireless relay networks since each single-antenna relay forwards simultaneously a different subset of source messages to the destination. In this paper, the performance of CSM with amplify-and-forward (AF) relays are presented. Specifically, we derive exact closed-form expressions for symbol error probability (SEP) and achievable spectral efficiency of CSM with linear receiver in dissimilar Rayleigh fading channels. Assessing the SEP performance in the high signal-to-noise regime, we further show that CSM with AF relays obtains the first order of diversity gain. Furthermore, it has been observed that CSM outperforms two well-known cooperative diversity systems, e.g., selection combining and maximal ratio combining, in term of spectral efficiency. We also perform Monte-Carlo simulations to validate our analysis.
|
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| 67. |
- Duong, Quang Trung, et al.
(författare)
-
Performance of Cognitive Radio Networks with Maximal Ratio Combining over Correlated Rayleigh Fading
- 2010
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we apply the maximal ratio combining (MRC) technique to achieve higher detection probability in cognitive radio networks over correlated Rayleigh fading channels. We present a simple approach to derive the probability of detection in closed-form expression. The numerical results reveal that the detection performance is a monotonically increasing function with respect to the number of antennas. Moreover, we provide sets of complementary receiver operating characteristic (ROC) curves to illustrate the effect of antenna correlation on the sensing performance of cognitive radio networks employing MRC schemes in some respective scenarios.
|
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| 68. |
- Duong, Quang Trung, et al.
(författare)
-
Replication Strategies for Video On-Demand over Wireless Mesh Networks : A Cross-Layer Optimization Approach
- 2012
-
Ingår i: Using Cross-Layer Techniques for Communication Systems. - : IGI. - 9781466609600 ; , s. 349-375
-
Bokkapitel (refereegranskat)abstract
- In this chapter, dependencies between the different protocol layers and across the hops through WMNs will be exploited to deliver video streaming with high QoE. Specifically, a cross-layer optimization approach is applied to a replication strategy for video on-demand over WMNs. Additionally, the authors consider a distributed implementation algorithm, namely Mod&Timer, to handle the placement of replicas for saving storage resources of the network. Simulation results are shown to demonstrate that the proposed cross-layer design outperforms many existing schemes in terms of QoE. More importantly, compared to other strategies without cross-layer interaction, the proposed cross-layer design satisfies the heterogeneous bandwidth constraint of end users.
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| 69. |
- Duong, Quang Trung, et al.
(författare)
-
Robust EZW Image Transmission Scheme Using Distributed-Alamouti Codes in Relay Networks
- 2008
-
Konferensbidrag (refereegranskat)abstract
- A robust image transmission scheme deploying distributed-Alamouti space-time code (STC) over wireless relay networks is proposed. Specifically, we propose a cross-layer design combining application, networking, and physical layer to enhance the quality of multimedia data over error-prone wireless channels. At the application layer, a coded image sequence based on the wavelet transform is divided into two priorities. The higher priority contains the most significant information of image and the lower priority conveys less important information. At the physical layer, two pre-assigned relays cooperate to form a distributed-Alamouti code which help the source to transmit the low priority sequence of the image over error-prone wireless channels. At the networking layer, among the whole relay nodes in the networks we select two relay nodes which provides the maximum signal-to-noise ratio to convey the higher priority. With this strategy, we implicitly achieve unequal error protection for image transmission without controlling power or varying modulation and coding at the transmitter at the expense of increasing network's overhead (i.e. feedback information). The selection of relays needs limited feedback, hence, enabling our proposed scheme feasible in practical applications. Analytical and simulation results are provided to verify our proposal. It has been shown that the image quality is remarkably enhanced in terms of objective quality using the proposed scheme compared to the conventional transmission schemes.
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| 70. |
- Duong, Quang Trung, et al.
(författare)
-
Symbol error probability of hop-by-hop beamforming in Nakagami-m fading
- 2009
-
Ingår i: Electronics Letters. - : The Institution of Engineering and Technology. - 0013-5194 .- 1350-911X. ; 45:20, s. 1042-1044
-
Tidskriftsartikel (refereegranskat)abstract
- The symbol error probability (SEP) of amplify-and-forward(AF) multiple-input multiple-output (MIMO) cooperative networks where beamforming is adopted at both the source and destination is investigated. In particular, the tight lower bound for SEP of AF MIMO relay systems is presented with hop-by-hop beamforming over independent, but not necessarily identically distributed, Nakagami-m fading channels. Furthermore, assessing the high SNR, an asymptotic SEP expression is derived which reveals the array and diversity gain. Numerical results are shown to verify the analysis in some representative scenarios.
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| 71. |
- 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.
|
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| 72. |
- Duong, Trung Quang, et al.
(författare)
-
MIMO Amplify-and-Forward Relay Systems with Dissimilar Channel Characteristics
- 2014
-
Ingår i: 2014 INTERNATIONAL CONFERENCE ON COMPUTING, MANAGEMENT AND TELECOMMUNICATIONS (COMMANTEL). - : IEEE. - 9781479929047 ; , s. 67-69
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the asymmetric property of multiple-input multiple-output (MIMO) dual-hop amplify-and- forward (AF) relay networks. We consider the difference of the two hops in terms of both fading channels and scattering environment. In particular, we analyze the symbol error probability (SEP) of a MIMO orthogonal space-time block code (OSTBC) AF relay network in which the first and second hop undergo Rayleigh fading with a rich-scattering environment and Nakagami-m fading with a poor-scattering environment, respectively. Moreover, an asymptotic SEP expression yielding insights on the diversity gain is also obtained.
|
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| 73. |
- 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.
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| 74. |
- 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.
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| 75. |
- 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.
|
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| 76. |
- 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.
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| 77. |
- 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.
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| 78. |
- 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.
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| 79. |
- 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.
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| 80. |
- 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.
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| 81. |
- Engelke, Ulrich, et al.
(författare)
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Multi-resolution Structural Degradation Metrics for Perceptual Image Quality Assessment
- 2007
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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.
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| 82. |
- Engelke, Ulrich, et al.
(författare)
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Multiobjective Optimization of Multiple Scale Visual Quality Processing
- 2008
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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.
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| 83. |
- Engelke, Ulrich, et al.
(författare)
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On Confidence and Response Times of Human Observers in Subjective Image Quality Assessment
- 2009
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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.
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| 84. |
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| 85. |
- Engelke, Ulrich, et al.
(författare)
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Optimal Region-of-Interest Based Visual Quality Assessment
- 2009
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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.
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| 86. |
- Engelke, Ulrich, et al.
(författare)
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Pareto Optimal Weighting of Structural Impairments for Wireless Imaging Quality Assessment
- 2008
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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.
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| 87. |
- Engelke, Ulrich, et al.
(författare)
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Perceptual-based Quality Metrics for Image and Video Services : A Survey
- 2007
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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.
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| 88. |
- Engelke, Ulrich, et al.
(författare)
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Perceptual Evaluation of Motion JPEG2000 Quality over Wireless Channels
- 2006
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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.
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| 89. |
- Engelke, Ulrich, et al.
(författare)
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Perceptual Quality Assessment of Wireless Video Applications
- 2006
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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.
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| 90. |
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| 91. |
- Engelke, Ulrich, et al.
(författare)
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Psychophysical Assessment of Perceived Interest in Natural Images : The ROI-D Database
- 2011
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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.
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| 92. |
- Engelke, Ulrich, et al.
(författare)
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Quality Assessment of an Adaptive Filter for Artifact Reduction in Mobile Video Sequences
- 2007
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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.
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| 93. |
- Engelke, Ulrich, et al.
(författare)
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Quality Evaluation in Wireless Imaging Using Feature-Based Objective Metrics
- 2007
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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.
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| 94. |
- Engelke, Ulrich, et al.
(författare)
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Quality of Experience of Multimedia Services : Past, Present, and Future
- 2011
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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.
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| 95. |
- Engelke, Ulrich, et al.
(författare)
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Reduced-reference metric design for objective perceptual quality assessment in wireless imaging
- 2009
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Ingår i: Signal Processing-Image Communication. - : ELSEVIER. - 0923-5965. ; 24:7, s. 525-547
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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.
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| 96. |
- Engelke, Ulrich, et al.
(författare)
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Regional Attention to Structural Degradations for Perceptual Image Quality Metric Design
- 2008
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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.
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| 97. |
- Engelke, Ulrich, et al.
(författare)
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Subjective Quality Assessment for Wireless Image Communication : The Wireless Imaging Quality Database
- 2010
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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.
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| 98. |
- Engelke, Ulrich, et al.
(författare)
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The Effect of Spatial Distortion Distributions on Human Viewing Behaviour when Judging Image Quality
- 2009
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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.
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| 99. |
- Engelke, Ulrich, et al.
(författare)
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Visual Attention in Quality Assessment
- 2011
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Ingår i: IEEE signal processing magazine (Print). - : IEEE. - 1053-5888 .- 1558-0792. ; 28:6, s. 50-59
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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.
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| 100. |
- Engelke, Ulrich, et al.
(författare)
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Visual Attention Modeling : Region-of-Interest Versus Fixation Patterns
- 2009
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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.
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