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In a typical communication pipeline, images undergo a series of processing steps that can cause visual distortions before being viewed. Given a high quality reference image, a reference (R) image quality assessment (IQA) algorithm can be applied after compression or transmission. However, the assumption of a high quality reference image is often not fulfilled in practice, thus contributing to less accurate quality predictions when using stand-alone R IQA models. This is particularly common on social media, where hundreds of billions of user-generated photos and videos containing diverse, mixed distortions are uploaded, compressed, and shared annually on sites like Facebook, YouTube, and Snapchat. The qualities of the pictures that are uploaded to these sites vary over a very wide range. While this is an extremely common situation, the problem of assessing the qualities of compressed images against their pre-compressed, but often severely distorted (reference) pictures has been little studied. Towards ameliorating this problem, we propose a novel two-step image quality prediction concept that combines NR with R quality measurements. Applying a first stage of NR IQA to determine the possibly degraded quality of the source image yields information that can be used to quality-modulate the R prediction to improve its accuracy. We devise a simple and efficient weighted product model of R and NR stages, which combines a pre-compression NR measurement with a post-compression R measurement. This first-of-a-kind two-step approach produces more reliable objective prediction scores. We also constructed a new, first-of-a-kind dedicated database specialized for the design and testing of two-step IQA models. Using this new resource, we show that two-step approaches yield outstanding performance when applied to compressed images whose original, pre-compression quality covers a wide range of realistic distortion types and severities. The two-step concept is versatile as it can use any desired R and NR components. We are making the source code of a particularly efficient model that we call 2stepQA publicly available at https://github.com/xiangxuyu/2stepQA. We are also providing the dedicated new two-step database free of charge at http://live.ece.utexas.edu/research/twostep/index.html. [ABSTRACT FROM AUTHOR]

We develop a model that expresses the joint impact of spatial resolution $s$ and JPEG compression quality factor $q^{f}$ on immersive image quality. The model is expressed as the product of optimized exponential functions of these factors. The model is tested on a subjective database of immersive image contents rendered on a head mounted display. High Pearson correlation and Spearman correlation (>0.95) and small relative root mean squared error (<5.6%) are achieved between the model predictions and the subjective quality judgements. The immersive ground-truth images along with the rest of the database are made available for future research and comparisons. [ABSTRACT FROM AUTHOR]

We announce a new video quality model (VQM) that accounts for the perceptual impact of variable frame delays (VFD) in videos with demonstrated top performance on the laboratory for image and video engineering (LIVE) mobile video quality assessment (VQA) database. This model, called VQM_VFD, uses perceptual features extracted from spatial-temporal blocks spanning fixed angular extents and a long edge detection filter. VQM_VFD predicts video quality by measuring multiple frame delays using perception based parameters to track subjective quality over time. In the performance analysis of VQM_VFD, we evaluated its efficacy at predicting human opinions of visual quality. A detailed correlation analysis and statistical hypothesis testing show that VQM_VFD accurately predicts human subjective judgments and substantially outperforms top-performing image quality assessment and VQA models previously tested on the LIVE mobile VQA database. VQM_VFD achieved the best performance on the mobile and tablet studies of the LIVE mobile VQA database for simulated compression, wireless packet-loss, and rate adaptation, but not for temporal dynamics. These results validate the new model and warrant a hard release of the VQM_VFD algorithm. It is freely available for any purpose, commercial, or noncommercial at http://www.its.bldrdoc.gov/vqm/. [ABSTRACT FROM PUBLISHER]

It is generally recognized that severe video distortions that are transient in space and/or time have a large effect on overall perceived video quality. In order to understand this phenomena, we study the distribution of spatio-temporally local quality scores obtained from several video quality assessment (VQA) algorithms on videos suffering from compression and lossy transmission over communication channels. We propose a content adaptive spatial and temporal pooling strategy based on the observed distribution. Our method adaptively emphasizes “worst” scores along both the spatial and temporal dimensions of a video sequence and also considers the perceptual effect of large-area cohesive motion flow such as egomotion. We demonstrate the efficacy of the method by testing it using three different VQA algorithms on the LIVE Video Quality database and the EPFL-PoliMI video quality database. [ABSTRACT FROM PUBLISHER]

We propose a natural scene statistic-based distortion-generic blind/no-reference (NR) image quality assessment (IQA) model that operates in the spatial domain. The new model, dubbed blind/referenceless image spatial quality evaluator (BRISQUE) does not compute distortion-specific features, such as ringing, blur, or blocking, but instead uses scene statistics of locally normalized luminance coefficients to quantify possible losses of “naturalness” in the image due to the presence of distortions, thereby leading to a holistic measure of quality. The underlying features used derive from the empirical distribution of locally normalized luminances and products of locally normalized luminances under a spatial natural scene statistic model. No transformation to another coordinate frame (DCT, wavelet, etc.) is required, distinguishing it from prior NR IQA approaches. Despite its simplicity, we are able to show that BRISQUE is statistically better than the full-reference peak signal-to-noise ratio and the structural similarity index, and is highly competitive with respect to all present-day distortion-generic NR IQA algorithms. BRISQUE has very low computational complexity, making it well suited for real time applications. BRISQUE features may be used for distortion-identification as well. To illustrate a new practical application of BRISQUE, we describe how a nonblind image denoising algorithm can be augmented with BRISQUE in order to perform blind image denoising. Results show that BRISQUE augmentation leads to performance improvements over state-of-the-art methods. A software release of BRISQUE is available online: http://live.ece.utexas.edu/research/quality/BRISQUE_release.zip for public use and evaluation. [ABSTRACT FROM AUTHOR]

Our approach to blind image quality assessment (IQA) is based on the hypothesis that natural scenes possess certain statistical properties which are altered in the presence of distortion, rendering them un-natural; and that by characterizing this un-naturalness using scene statistics, one can identify the distortion afflicting the image and perform no-reference (NR) IQA. Based on this theory, we propose an (NR)/blind algorithm—the Distortion Identification-based Image Verity and INtegrity Evaluation (DIIVINE) index—that assesses the quality of a distorted image without need for a reference image. DIIVINE is based on a 2-stage framework involving distortion identification followed by distortion-specific quality assessment. DIIVINE is capable of assessing the quality of a distorted image across multiple distortion categories, as against most NR IQA algorithms that are distortion-specific in nature. DIIVINE is based on natural scene statistics which govern the behavior of natural images. In this paper, we detail the principles underlying DIIVINE, the statistical features extracted and their relevance to perception and thoroughly evaluate the algorithm on the popular LIVE IQA database. Further, we compare the performance of DIIVINE against leading full-reference (FR) IQA algorithms and demonstrate that DIIVINE is statistically superior to the often used measure of peak signal-to-noise ratio (PSNR) and statistically equivalent to the popular structural similarity index (SSIM). A software release of DIIVINE has been made available online: xlink:type="simple" xlink:href="http://live.ece.utexas.edu/research/quality/DIIVINE_release.zip" xmlns:xlink="http://www.w3.org/1999/xlink"http://live.ece.utexas.edu/research/quality/DIIVINE_release.zip for public use and evaluation. [ABSTRACT FROM AUTHOR]

We develop a no-reference image quality assessment (QA) algorithm that deploys a general regression neural network (GRNN). The new algorithm is trained on and successfully assesses image quality, relative to human subjectivity, across a range of distortion types. The features deployed for QA include the mean value of phase congruency image, the entropy of phase congruency image, the entropy of the distorted image, and the gradient of the distorted image. Image quality estimation is accomplished by approximating the functional relationship between these features and subjective mean opinion scores using a GRNN. Our experimental results show that the new method accords closely with human subjective judgment. [ABSTRACT FROM AUTHOR]

We study the efficiency of deblocking algorithms for improving visual signals degraded by blocking artifacts from compression. Rather than using only the perceptually questionable PSNR, we instead propose a block-sensitive index, named PSNR-B, that produces objective judgments that accord with observations. The PSNR-B modifies PSNR by including a blocking effect factor. We also use the perceptually significant SSIM index, which produces results largely in agreement with PSNR-B. Simulation results show that the PSNR-B results in better performance for quality assessment of deblocked images than PSNR and a well-known blockiness-specific index. [ABSTRACT FROM AUTHOR]

We survey recent developments in multimedia signal quality assessment, including image, audio, video, and combined signals. Such an overview is timely given the recent explosion in all-digital sensory entertainment and communication devices pervading the consumer space. Owing to the sensory nature of these signals, perceptual models lie at the heart of multimedia signal quality assessment algorithms. We survey these models and recent competitive algorithms and discuss comparison studies that others have conducted. In this context we also describe existing signal quality assessment databases. We envision that the reader will gain a firmer understanding of the broad topic of multimedia quality assessment, of the various sub-disciplines corresponding to different signal types, how these signals types co-relate in producing an overall user experience, and what directions of research remain to be pursued. [ABSTRACT FROM AUTHOR]

We propose a new video quality assessment (VQA) algorithm—the motion compensated structural similarity index—that assesses not only spatial quality but also quality along temporal trajectories. Drawing inspiration from the motion-compensated approach followed for video compression, we propose a motion-compensated approach to temporal quality assessment. The proposed algorithm is computationally efficient as compared to other VQA algorithms that utilize motion information from extracted optical flow and correlates well with human perception of quality. In order to exemplify the utility of the algorithm in a practical setting, we evaluate the quality of H.264/AVC compressed videos. Efficiency of computation is enabled by the novel motion-vector re-use concept. [ABSTRACT FROM PUBLISHER]

Evaluating the perceptual quality of video is of tremendous importance in the design and optimization of wireless video processing and transmission systems. In an endeavor to emulate human perception of quality, various objective video quality assessment (VQA) algorithms have been developed. However, the only subjective video quality database that exists on which these algorithms can be tested is dated and does not accurately reflect distortions introduced by present generation encoders and/or wireless channels. In order to evaluate the performance of VQA algorithms for the specific task of H.264 advanced video coding compressed video transmission over wireless networks, we conducted a subjective study involving 160 distorted videos. Various leading full reference VQA algorithms were tested for their correlation with human perception. The data from the paper has been made available to the research community, so that further research on new VQA algorithms and on the general area of VQA may be carried out. [ABSTRACT FROM AUTHOR]

Measurement of visual quality is of fundamental importance for numerous image and video processing applications, where the goal of quality assessment (QA) algorithms is to automatically assess the quality of images or videos in agreement with human quality judgments. Over the years, many researchers have taken different approaches to the problem and have contributed significant research in this area and claim to have made progress in their respective domains. It is important to evaluate the performance of these algorithms in a comparative setting and analyze the strengths and weaknesses of these methods. In this paper, we present results of an extensive subjective quality assessment study in which a total of 779 distorted images were evaluated by about two dozen human subjects. The "ground truth" image quality data obtained from about 25000 individual human quality judgments is used to evaluate the performance of several prominent full-reference image quality assessment algorithms. To the best of our knowledge, apart from video quality studies conducted by the Video Quality Experts Group, the study presented in this paper is the largest subjective image quality study in the literature in terms of number of images, distortion types, and number of human judgments per image. Moreover, we have made the data from the study freely available to the research community [1]. This would allow other researchers to easily report comparative results in the future. [ABSTRACT FROM AUTHOR]

We develop a new model for no-reference 3D stereopair quality assessment that considers the impact of binocular fusion, rivalry, suppression, and a reverse saliency effect on the perception of distortion. The resulting framework, dubbed the S3D INtegrated Quality (SINQ) Predictor, first fuses the left and right views of a stereopair into a single synthesized cyclopean image using a novel modification of an existing binocular perceptual model. Specifically, the left and right views of a stereopair are fused using a measure of “cyclopean” spatial activity. A simple product estimate is also calculated as the correlation between left and right disparity-corrected corresponding binocular pixels. Univariate and bivariate statistical features are extracted from the four available image sources: the left view, the right view, the synthesized “cyclopean” spatial activity image, and the binocular product image. Based on recent evidence regarding the placement of 3D fixation by subjects viewing stereoscopic 3D (S3D) content, we also deploy a reverse saliency weighting on the normalized “cyclopean” spatial activity image. Both one- and two-stage frameworks are then used to map the feature vectors to predicted quality scores. SINQ is thoroughly evaluated on the LIVE 3D image quality database (Phase I and Phase II). The experimental results show that SINQ delivers better performance than state of the art 2D and 3D quality assessment methods on six public databases, especially on asymmetric distortions. [ABSTRACT FROM AUTHOR]

The image gradient is a commonly computed image feature and a potentially predictive factor for image quality assessment (IQA). Indeed, it has been successfully used for both full- and no- reference image quality prediction. However, the gradient orientation has not been deeply explored as a predictive source of information for image quality assessment. Here we seek to amend this by studying the quality relevance of the relative gradient orientation, viz., the gradient orientation relative to the surround. We also deploy a relative gradient magnitude feature which accounts for perceptual masking and utilize an AdaBoosting back-propagation (BP) neural network to map the image features to image quality. The generalization of the AdaBoosting BP neural network results in an effective and robust quality prediction model. The new model, called Oriented Gradients Image Quality Assessment (OG-IQA), is shown to deliver highly competitive image quality prediction performance as compared with the most popular IQA approaches. Furthermore, we show that OG-IQA has good database independence properties and a low complexity. [ABSTRACT FROM AUTHOR]

We develop an efficient general-purpose no-reference (NR) image quality assessment (IQA) model that utilizes local spatial and spectral entropy features on distorted images. Using a 2-stage framework of distortion classification followed by quality assessment, we utilize a support vector machine (SVM) to train an image distortion and quality prediction engine. The resulting algorithm, dubbed Spatial–Spectral Entropy-based Quality (SSEQ) index, is capable of assessing the quality of a distorted image across multiple distortion categories. We explain the entropy features used and their relevance to perception and thoroughly evaluate the algorithm on the LIVE IQA database. We find that SSEQ matches well with human subjective opinions of image quality, and is statistically superior to the full-reference (FR) IQA algorithm SSIM and several top-performing NR IQA methods: BIQI, DIIVINE, and BLIINDS-II. SSEQ has a considerably low complexity. We also tested SSEQ on the TID2008 database to ascertain whether it has performance that is database independent. [ABSTRACT FROM AUTHOR]

Abstract: Stereoscopic/3D image and video quality assessment (IQA/VQA) has become increasing relevant in today's world, owing to the amount of attention that has recently been focused on 3D/stereoscopic cinema, television, gaming, and mobile video. Understanding the quality of experience of human viewers as they watch 3D videos is a complex and multi-disciplinary problem. Toward this end we offer a holistic assessment of the issues that are encountered, survey the progress that has been made towards addressing these issues, discuss ongoing efforts to resolve them, and point up the future challenges that need to be focused on. Important tools in the study of the quality of 3D visual signals are databases of 3D image and video sets, distorted versions of these signals and the results of large-scale studies of human opinions of their quality. We explain the construction of one such tool, the LIVE 3D IQA database, which is the first publicly available 3D IQA database that incorporates ‘true’ depth information along with stereoscopic pairs and human opinion scores. We describe the creation of the database and analyze the performance of a variety of 2D and 3D quality models using the new database. The database as well as the algorithms evaluated are available for researchers in the field to use in order to enable objective comparisons of future algorithms. Finally, we broadly summarize the field of 3D QA focusing on key unresolved problems including stereoscopic distortions, 3D masking, and algorithm development. [Copyright &y& Elsevier]