| 1. |
- Andersson, Kenneth, 1970-, et al.
(author)
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Motion compensation using backward prediction and prediction refinement
- 2003
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In: Signal Processing: Image Communication. - 0923-5965. ; 18:5, s. 381-400
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Journal article (peer-reviewed)abstract
- This paper presents new methods for use of dense motion fields for motion compensation of interlaced video. The motion estimation is based on previously decoded field-images. The motion is then temporally predicted and used for motion compensated prediction of the field-image to be coded. The motion estimation algorithm is phase-based and uses two or three field-images to achieve motion estimates with sub-pixel accuracy. To handle non-constant motion and the specific characteristics of the field-image to be coded, the initially predicted image is refined using forward motion compensation, based on block-matching. Tests show that this approach achieves higher PSNR than forward block-based motion estimation, when coding the residual with the same coder. The subjective performance is also better.
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| 2. |
- Bergström, Peter
(author)
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Eye-movement-controlled transform image coders
- 2003
-
In: Signal processing. Image communication. - 0923-5965 .- 1879-2677. ; 18:2, s. 115-125
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Journal article (peer-reviewed)abstract
- An image-coding scheme which combines transform coding with a human visual system (HVS) model is described. The system includes an eye tracker to pick up the point of regard of a single viewer. One can then utilize that the acuity of the HVS is less in the peripheral vision than in the central part of the visual field. A model of the decreasing acuity of the HVS, which can be applied to a wide class of transform coders is described. Such a coding system has large potential for data compression. In this paper, we have incorporated the model into four different transform coders, one from each of the main classes of transform coders. Two of the coders are block-based decomposition schemes, the discrete cosine transform-based JPEG coder and a lapped transform scheme. The two others are subband-based decomposition schemes, a wavelet based and a wavelet packet-based scheme. © 2002 Elsevier Science B.V. All rights reserved.
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| 3. |
- Jennehag, Ulf, et al.
(author)
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Numerical modeling of transmission errors and video quality of MPEG-2
- 2001
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In: Signal processing. Image communication. - 0923-5965 .- 1879-2677. ; 16:8, s. 817-825
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Journal article (peer-reviewed)abstract
- To efficiently combat the signal loss of MPEG-2 transmission over unreliable networks, priority encoding transmission, unequal packet loss protection and priority dropping techniques have been studied in many papers. Those studies are based on the qualitative analysis of different importance of signals, without quantitative investigation of signal loss effect on video quality. In this paper, MPEG-2 packet loss effect on video quality is quantitatively investigated, a temporal layered signal model is described and evaluated, a quality measure for reconstructed pictures called macroblock impairment ratio is suggested and defined. The investigation and the model are specified for MPEG-2, but the principles and the methods are suitable for any layered video. These are useful for the development of efficient schemes and protocols for packet video transmission over unreliable networks.
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| 4. |
- Brunnström, Kjell, 1960-, et al.
(author)
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Latency impact on Quality of Experience in a virtual reality simulator for remote control of machines
- 2020
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In: Signal processing. Image communication. - : Elsevier. - 0923-5965 .- 1879-2677. ; 89
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Journal article (peer-reviewed)abstract
- In this article, we have investigated a VR simulator of a forestry crane used for loading logs onto a truck. We have mainly studied the Quality of Experience (QoE) aspects that may be relevant for task completion, and whether there are any discomfort related symptoms experienced during the task execution. QoE experiments were designed to capture the general subjective experience of using the simulator, and to study task performance. The focus was to study the effects of latency on the subjective experience, with regards to delays in the crane control interface. Subjective studies were performed with controlled delays added to the display update and hand controller (joystick) signals. The added delays ranged from 0 to 30 ms for the display update, and from 0 to 800 ms for the hand controller. We found a strong effect on latency in the display update and a significant negative effect for 800 ms added delay on latency in the hand controller (in total approx. 880 ms latency including the system delay). The Simulator Sickness Questionnaire (SSQ) gave significantly higher scores after the experiment compared to before the experiment, but a majority of the participants reported experiencing only minor symptoms. Some test subjects ceased the test before finishing due to their symptoms, particularly due to the added latency in the display update.
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| 5. |
- Chien, Trinh Van, et al.
(author)
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Block compressive sensing of image and video with nonlocal Lagrangian multiplier and patch-based sparse representation
- 2017
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In: Signal processing. Image communication. - : ELSEVIER SCIENCE BV. - 0923-5965 .- 1879-2677. ; 54, s. 93-106
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Journal article (peer-reviewed)abstract
- Although block compressive sensing (BCS) makes it tractable to sense large-sized images and video, its recovery performance has yet to be significantly improved because its recovered images or video usually suffer from blurred edges, loss of details, and high-frequency oscillatory artifacts, especially at a low subrate. This paper addresses these problems by designing a modified total variation technique that employs multi-block gradient processing, a denoised Lagrangian multiplier, and patch-based sparse representation. In the case of video, the proposed recovery method is able to exploit both spatial and temporal similarities. Simulation results confirm the improved performance of the proposed method for compressive sensing of images and video in terms of both objective and subjective qualities.
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| 6. |
- Engelke, Ulrich, et al.
(author)
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Human Observer Confidence in Image Quality Assessment
- 2012
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In: Signal processing. Image communication. - : Elsevier. - 0923-5965 .- 1879-2677. ; 27:9, s. 935-947
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Journal article (peer-reviewed)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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| 7. |
- Engelke, Ulrich, et al.
(author)
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Reduced-reference metric design for objective perceptual quality assessment in wireless imaging
- 2009
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In: Signal Processing-Image Communication. - : ELSEVIER. - 0923-5965. ; 24:7, s. 525-547
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Journal article (peer-reviewed)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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| 8. |
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| 9. |
- Fu, Keren, 1988, et al.
(author)
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Superpixel based color contrast and color distribution driven salient object detection
- 2013
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In: Signal Processing: Image Communication. - : Elsevier BV. - 0923-5965. ; 28:10, s. 1448-1463
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Journal article (peer-reviewed)abstract
- Color is the most informative low-level feature and might convey tremendous saliency information of a given image. Unfortunately, color feature is seldom fully exploited in the previous saliency models. Motivated by the three basic disciplines of a salient object which are respectively center distribution prior, high color contrast to surroundings and compact color distribution, in this paper, we design a comprehensive salient object detection system which takes the advantages of color contrast together with color distribution and outputs high quality saliency maps. The overall procedure flow of our unified framework contains superpixel pre-segmentation, color contrast and color distribution computation, combination, and final refinement. In color contrast saliency computation, we calculate center-surrounded color contrast and then employ the distribution prior in order to select correct color components. A global saliency smoothing procedure that is based on superpixel regions is introduced as well. This processing step preferably alleviates the saliency distortion problem, leading to the entire object being highlighted uniformly. Finally, a saliency refinement approach is adopted to eliminate artifacts and recover unconnected parts within the combined saliency maps. In visual comparison, our method produces higher quality saliency maps which stress out the total object meanwhile suppress background clutter. Both qualitative and quantitative experiments show our approach outperforms 8 state-of-the-art methods, achieving the highest precision rate 96% (3% improvement from the current highest), when evaluated via one of the most popular data sets. Excellent content-aware image resizing also could be achieved using our saliency maps. (C) 2013 Elsevier B.V. All rights reserved.
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| 10. |
- Gao, Shan, et al.
(author)
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A TV regularisation sparse light field reconstruction model based on guided-filtering
- 2022
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In: Signal processing. Image communication. - : Elsevier BV. - 0923-5965 .- 1879-2677. ; 109
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Journal article (peer-reviewed)abstract
- Obtaining and representing the 4D light field is important for a number of computer vision applications. Due to the high dimensionality, acquiring the light field directly is costly. One way to overcome this deficiency is to reconstruct the light field from a limited number of measurements. Existing approaches involve either a depth estimation process or require a large number of measurements to obtain high-quality reconstructed results. In this paper, we propose a total variation (TV) regularisation sparse model with the alternating direction method of multipliers (ADMM) based on guided filtering, which addresses this depth-dependence problem with only a few measurements. As one of the sparse optimisation methods, TV regularisation based on ADMM is well suited to solve ill-posed problems such as this. Moreover, guided filtering has good edge-preserving smoothing properties, which can be incorporated into the light field reconstruction process. Therefore, high precision light field reconstruction is established with our model. Specifically, the updated image in the iteration step contains the guidance image, and an initialiser for the least squares method using a QR factorisation (LSQR) algorithm is involved in one of the subproblems. The model outperforms other methods in both visual assessments and objective metrics – in simulation experiments from synthetic data and photographic data using produced focal stacks from light field contents – and it works well in experiments using captured focal stacks. We also show a further application for arbitrary refocusing by using the reconstructed light field.
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