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Reduced-reference (RR) image quality assessment (IQA) aims to use less reference data for quality evaluation. Global features are demanded to effectively express quality degradation caused by distortion. Since the human visual system (HVS) is highly sensitive to structure degradation, we suggest to represent the visual content of an image with several structural patterns. Also, image quality is measured based on the structural degradation on these patterns. Firstly, the spatial correlation of image structure is analyzed with the local binary pattern (LBP), and several representative structural patterns are extracted. Then, the energy changes on these patterns between the reference image and the distorted image are calculated. Finally, the support vector regression (SVR) procedure is adopted for feature pooling, and the quality score of the input image is returned. Experimental results for three publicly available databases demonstrate that the proposed RR IQA method is highly consistent with the human perception, which uses a small amount of reference data (20 values) and achieves a promising improvement on quality evaluation accuracy. [ABSTRACT FROM AUTHOR]

Recent advances in sparse representation show that overcomplete dictionaries learned from natural images can capture high-level features for image analysis. Since atoms in the dictionaries are typically edge patterns and image blur is characterized by the spread of edges, an overcomplete dictionary can be used to measure the extent of blur. Motivated by this, this paper presents a no-reference sparse representation-based image sharpness index. An overcomplete dictionary is first learned using natural images. The blurred image is then represented using the dictionary in a block manner, and block energy is computed using the sparse coefficients. The sharpness score is defined as the variance-normalized energy over a set of selected high-variance blocks, which is achieved by normalizing the total block energy using the sum of block variances. The proposed method is not sensitive to training images, so a universal dictionary can be used to evaluate the sharpness of images. Experiments on six public image quality databases demonstrate the advantages of the proposed method. [ABSTRACT FROM PUBLISHER]

Reduced-reference (RR) image quality assessment (IQA) aims to use less data about the reference image and achieve higher evaluation accuracy. Recent research on brain theory suggests that the human visual system (HVS) actively predicts the primary visual information and tries to avoid the residual uncertainty for image perception and understanding. Therefore, the perceptual quality relies to the information fidelities of the primary visual information and the residual uncertainty. In this paper, we propose a novel RR IQA index based on visual information fidelity. We advocate that distortions on the primary visual information mainly disturb image understanding, and distortions on the residual uncertainty mainly change the comfort of perception. We separately compute the quantities of the primary visual information and the residual uncertainty of an image. Then the fidelities of the two types of information are separately evaluated for quality assessment. Experimental results demonstrate that the proposed index uses few data (30 bits) and achieves high consistency with human perception. [ABSTRACT FROM PUBLISHER]

Recent mapping-based motion deblurring methods lack the regularization of prior knowledge, resulting in an over-reliance on the training data and limited generalization ability. As deblurring aims to improve image quality, we quantitatively analyze and further discover the strong correlation between image quality and sharpness. Motivated by the above facts and notable accomplishments of recent no-reference image quality assessment (NR-IQA), we present a novel framework that incorporates quality knowledge into mapping-based deblurring models. Specifically, we extract quality-aware features from NR-IQA models as prior knowledge, and subsequently propose a prediction-based strategy and an encoder-reuse strategy to integrate knowledge into the encoder and decoder, respectively. After training, the model can simultaneously deblur images and predict quality features, indicating that it has grasped the knowledge and validating the effectiveness of the proposed embedding strategies. Extensive experimental results show that embedding quality knowledge consistently improves model performance and the model achieves state-of-the-art intra/cross-dataset results. Code and pre-trained models are available at https://github.com/esnthere/QAMD. • Integrating no-reference image quality assessment into image deblurring. • Prediction-based strategy for encoder knowledge embedding. • Encoder-reuse strategy for decoder knowledge embedding. • Simultaneously deblurring images and predicting quality features. • SOTA intra/cross-dataset test performance. [ABSTRACT FROM AUTHOR]

Compressive sensing (CS) has been attracting tremendous attention in recent years. Extensive CS image recovery algorithms have been proposed for more effective image reconstruction. However, very little work has been addressed for the quality assessment of CS recovered images, which may hinder further development of CS image recovery techniques. The CS recovered images are typically contaminated by multiple distortions, particularly at low sampling rates. Unfortunately, the existing quality metrics are ineffective for evaluating multiple distortions, so they are limited in predicting the quality of CS recovered images. Motivated by this, this paper presents a no-reference CS Recovered Image Quality (CSRIQ) metric based on the measurement of both local and global distortions in CS recovered images. The local features consist of a local phase coherence based edge sharpness measure and a gray level co-occurrence matrix based texture measure. The global features are extracted based on the natural scene statistics and can be divided into two types. One type is obtained by calculating image naturalness parameters. The other type is computed based on the statistics of singular value decomposition coefficients. Support vector regression is employed to do model training and the subsequent quality prediction. Experimental results conducted on a CS recovered image database demonstrate the advantages of the proposed method. As a application, the proposed metric is used for automatic parameter selection for CS image recovery algorithms. [ABSTRACT FROM AUTHOR]

Images are subject to blocking artifacts when they are compressed using the JPEG standard. Knowing the extent of blocking artifacts is thus necessary for such applications as automatic quality monitoring and restoration. The current blocking artifacts measures are based on a strong prior that the block boundaries are known in advance, which often does not hold in real-world applications. Therefore, their performances degrade significantly when block boundaries are misaligned. To address the problem, this paper presents a robust no-reference blocking artifacts evaluation metric for JPEG images based on grid strength and regularity (GridSAR). The underlying idea is to extract block grids from a JPEG image and quantify the grid image to evaluate the strength of blocking artifacts. To this end, a grid map of blocking artifacts is first extracted from the image in the spatial domain. Then the blocking artifacts of the image are evaluated by quantifying the strength and regularity of the grid image. Furthermore, in order to account for the varying sensitivities of human eyes to the blocking artifacts in smooth and textured areas, a masking function is also proposed. Experimental results on seven popular image quality databases demonstrate that GridSAR achieves the state-of-the-art performance, and is robust to block misalignments. [ABSTRACT FROM AUTHOR]

Image quality assessment (IQA) is a fundamental problem in image processing. While in practice almost all images are represented in the color format, most of the current IQA metrics are designed in gray-scale domain. Color influences the perception of image quality, especially in the case where images are subject to color distortions. With this consideration, this paper presents a novel color image quality index based on Sparse Representation and Reconstruction Residual (SRRR). An overcomplete color dictionary is first trained using natural color images. Then both reference and distorted images are represented using the color dictionary, based on which two feature maps are constructed to measure structure and color distortions in a holistic manner. With the consideration that the feature maps are insensitive to image contrast change, the reconstruction residuals are computed and used as a complementary feature. Additionally, luminance similarity is also incorporated to produce the overall quality score for color images. Experiments on public databases demonstrate that the proposed method achieves promising performance in evaluating traditional distortions, and it outperforms the existing metrics when used for quality evaluation of color-distorted images. [ABSTRACT FROM AUTHOR]

JPEG is the most commonly used image compression standard. In practice, JPEG images are easily subject to blocking artifacts at low bit rates. To reduce the blocking artifacts, many deblocking algorithms have been proposed. However, they also introduce certain degree of blur, so the deblocked images contain multiple distortions. Unfortunately, the current quality metrics are not designed for multiply distorted images, so they are limited in evaluating the quality of deblocked images. To solve the problem, this paper presents a no-reference (NR) quality metric for deblocked images. A DeBlocked Image Database (DBID) is first built with subjective Mean Opinion Score (MOS) as ground truth. Then a NR DeBlocked Image Quality (DBIQ) metric is proposed by simultaneously evaluating blocking artifacts in smooth regions and blur in textured regions. Experimental results conducted on the DBID database demonstrate that the proposed metric is effective in evaluating the quality of deblocked images, and it significantly outperforms the existing metrics. As an application, the proposed metric is further used for automatic parameter selection in image deblocking algorithms. [ABSTRACT FROM AUTHOR]