Abstract Good health is pursued by people all over the world. However, the continual industrialisation has led to more and more atmospheric contamination, and PM has caused serious harm to our life safety and living environment. Without increasing the cost of sustainable industrial production, more and more attention has been paid to the related researches on improving PM monitoring, prevention and control level. Therefore, it is extremely urgent to establish a robust PM monitoring model that can adapt to a variety of scenarios, not only in local places like campuses but also in wide area like city. Existing work has proven that PM monitoring can be achieved by means of photos. But experiments show that the stated‐of‐the‐art methods are far from ideal for PM monitoring when the author tested the performance in two public datasets. To solve the aforesaid issue, this paper ulteriorly proposes a novel photo‐based PM monitoring model, which fuses the results of existing methods by firstly using the weighted average based on the least absolute shrinkage and selection operator regression for learning the basic linear component, secondly using the support vector regression for learning the non‐linear residual component, and finally incorporating the above two outputs to infer the final PM concentration. The main contributions and innovations of this paper are embodied in: (1) the innovative use of image quality assessment model to extract 9 features for PM monitoring, (2) separately extract macro information and micro information from PM2.5 pictures, (3) two newly‐established large‐scaled datasets are applied to verify the effectiveness and robustness of the proposed PM monitoring model. Experiments show that on the latest PM datasets (local and wide), the proposed model has achieved high performance and demonstrated strong robustness.

This article devises a photograph-based monitoring model to estimate the real-time PM2.5concentrations, overcoming currently popular electrochemical sensor-based PM2.5monitoring methods’ shortcomings such as low-density spatial distribution and time delay. Combining the proposed monitoring model, the photographs taken by various camera devices (e.g., surveillance camera, automobile data recorder, and mobile phone) can widely monitor PM2.5concentration in megacities. This is beneficial to offering helpful decision-making information for atmospheric forecast and control, thus reducing the epidemic of COVID-19. To specify, the proposed model fuses Information Abundance measurement and Wide and Deep learning, dubbed as IAWD, for PM2.5monitoring. First, our model extracts two categories of features in a newly proposed DS transform space to measure the information abundance (IA) of a given photograph since the growth of PM2.5concentration decreases its IA. Second, to simultaneously possess the advantages of memorization and generalization, a new wide and deep neural network is devised to learn a nonlinear mapping between the above-mentioned extracted features and the groundtruth PM2.5concentration. Experiments on two recently established datasets totally including more than 100 000 photographs demonstrate the effectiveness of our extracted features and the superiority of our proposed IAWD model as compared to state-of-the-art relevant computing techniques.

Recent years have witnessed the spread of electronic devices especially the mobile phones, which have become almost the necessities in people's daily lives. An effective and efficient technique for blindly assessing the quality of display products is greatly helpful to improve the experiences of users, such as displaying the pictures or texts in a more comfortable manner. In this paper, we put forward a novel no-reference (NR) quality metric of display products, dubbed as NQMDP. First, we have established a new subjective photo quality database, in which 50 photos shown on three different types of display products were captured to constitute a total of 150 photos and then scored by more than 40 inexperienced observers. Second, 19 effective image features are extracted by using six different influencing factors (including complexity, contrast, sharpness, brightness, colorfulness and naturalness) on the quality of display products and then were learned with the support vector regressor (SVR) to estimate the objective quality score of each photo. Results of experiments show that our proposed method has obtained better performance than the state-of-the-art algorithms.

Free viewpoint video (FVV) has received considerable attention owing to its widespread applications in several areas such as immersive entertainment, remote surveillance and distanced education. Since FVV images are synthesized via a depth image-based rendering (DIBR) procedure in the "blind" environment (without reference images), a real-time and reliable blind quality assessment metric is urgently required. However, the existing image quality assessment metrics are insensitive to the geometric distortions engendered by DIBR. In this research, a novel blind method of DIBR-synthesized images is proposed based on measuring geometric distortion, global sharpness and image complexity. First, a DIBR-synthesized image is decomposed into wavelet subbands by using discrete wavelet transform. Then, the Canny operator is employed to detect the edges of the binarized low-frequency subband and high-frequency subbands. The edge similarities between the binarized low-frequency subband and high-frequency subbands are further computed to quantify geometric distortions in DIBR-synthesized images. Second, the log-energies of wavelet subbands are calculated to evaluate global sharpness in DIBR-synthesized images. Third, a hybrid filter combining the autoregressive and bilateral filters is adopted to compute image complexity. Finally, the overall quality score is derived to normalize geometric distortion and global sharpness by the image complexity. Experiments show that our proposed quality method is superior to the competing reference-free state-of-the-art DIBR-synthesized image quality models.

Smoke detection plays an important role in industrial safety warning systems and fire prevention. Due to the complicated changes in the shape, texture, and color of smoke, identifying the smoke from a given image still remains a substantial challenge, and this has accordingly aroused a considerable amount of research attention recently. To address the problem, we devise a new deep dual-channel neural network (DCNN) for smoke detection. In contrast to popular deep convolutional networks (e.g., Alex-Net, VGG-Net, Res-Net, and Dense-Net and the DNCNN that is specifically devoted to detecting smoke), our proposed end-to-end network is mainly composed of dual channels of deep subnetworks. In the first subnetwork, we sequentially connect multiple convolutional layers and max-pooling layers. Then, we selectively append the batch normalization layer to each convolutional layer for overfitting reduction and training acceleration. The first subnetwork is shown to be good at extracting the detailed information of smoke, such as texture. In the second subnetwork, in addition to the convolutional, batch normalization, and max-pooling layers, we further introduce two important components. One is the skip connection for avoiding the vanishing gradient and improving the feature propagation. The other is the global average pooling for reducing the number of parameters and mitigating the overfitting issue. The second subnetwork can capture the base information of smoke, such as contours. We finally deploy a concatenation operation to combine the aforementioned two deep subnetworks to complement each other. Based on the augmented data obtained by rotating the training images, our proposed DCNN can promptly and stably converge to the perfect performance. Experimental results conducted on the publicly available smoke detection database verify that the proposed DCNN has attained a very high detection rate that exceeds 99.5% on average, superior to state-of-the-art relevant competitors. Furthermore, our DCNN only employs approximately one-third of the parameters needed by the comparatively tested deep neural networks. The source code of DCNN will be released at https://kegu.netlify.com/.

Free viewpoint video (FVV), owing to its comprehensive applications in immersive entertainment, remote surveillance and distanced education, has received extensive attention and been regarded as a new important direction of video technology development. Depth image-based rendering (DIBR) technologies are employed to synthesize FVV images in the "blind" environment. Therefore, a real-time reliable blind quality assessment metric is urgently required. However, existing stste-of-art quality assessment methods are limited to estimate geometric distortions generated by DIBR. In this research, a novel blind quality metric, measuring Geometric Distortions and Image Complexity (GDIC), is proposed for DIBR-synthesized images. Firstly, a DIBR-synthesized image is decomposed into wavelet subbands by using discrete wavelet transform. Then, we adopt canny operator to capture the edge of wavelet subbands and compute the edge similarity between low-frequency subband and highfrequency subbands. The edge similarity is used to quantify geometric distortions in DIBR-synthesized images. Secondly, a hybrid filter combining the autoregressive and bilateral filter is adopted to compute image complexity. Finally, the overall quality score is calculated by normalizing geometric distortions via image complexity. Experiments show that our proposed GDIC is superior to prevailing image quality assessment metrics, which were intended for natural and DIBR-synthesized images.

With multitudes of image processing applications, image quality assessment (IQA) has become a prerequisite for obtaining maximally distinctive statistics from images. Despite the widespread research in this domain over several years, existing IQA algorithms have a number of key limitations concerning different image distortion types and algorithms' computational efficiency. Images that are synthesized using depth image-based rendering have applications in various disciplines, such as free viewpoint videos, which enable synthesis of novel realistic images in the referenceless environment. In the literature, very few no-reference (NR) quality assessment metrics of three-dimensional (3-D) synthesized images are proposed, and most of them are computationally expensive, which makes it difficult for them to be deployed in real-time applications. In this paper, we attribute the geometrically distorted pixels as outliers in 3-D synthesized images. This assumption is validated using the three $sigma$ rule-based robust outlyingness ratio. We propose a novel fast and accurate blind IQA metric of 3-D synthesized images using nonlinear median filtering since the median filtering has the capability of identifying and removing outliers. The advantages of the proposed algorithm are twofold. First, it uses a simple technique, i.e., median filtering, to capture the level of geometric and structural distortions (up to some extend). Second, the proposed algorithm has higher computational efficiency. Experiments show the superiority of the proposed NR IQA algorithm over existing state-of-the-art full-, reduced-, and NR IQA methods, in terms of both predicting accuracy and computational complexity.

Sonar imagery plays a significant role in oceanic applications since there is little natural light underwater, and light is irrelevant to sonar imaging. Sonar images are very likely to be affected by various distortions during the process of transmission via the underwater acoustic channel for further analysis. At the receiving end, the reference image is unavailable due to the complex and changing underwater environment and our unfamiliarity with it. To the best of our knowledge, one of the important usages of sonar images is target recognition on the basis of contour information. The contour degradation degree for a sonar image is relevant to the distortions contained in it. To this end, we developed a new no-reference contour degradation measurement for perceiving the quality of sonar images. The sparsities of a series of transform coefficient matrices, which are descriptive of contour information, are first extracted as features from the frequency and spatial domains. The contour degradation degree for a sonar image is then measured by calculating the ratios of extracted features before and after filtering this sonar image. Finally, a bootstrap aggregating (bagging)-based support vector regression module is learned to capture the relationship between the contour degradation degree and the sonar image quality. The results of experiments validate that the proposed metric is competitive with the state-of-the-art reference-based quality metrics and outperforms the latest reference-free competitors.

In this paper we propose to blindly evaluate the quality of images synthesized based on a depth image-based rendering (DIBR) procedure. As an important branch in virtual reality (VR), superior DIBR techniques provide free viewpoints in many real applications such as remote surveillance and education, but few efforts have been made to measure the performance of DIBR methods (i.e. the quality of DIBR-synthesized images), especially in the condition of reference unavailable. To this aim, we put forward a new no-reference (NR) image quality assessment (IQA) model via multiscale analysis, dubbed as MSA. The design philosophy of our proposed MSA model is that the DIBR-introduced geometry distortions damage the self-similarity characteristic of natural images and the damage degrees present regular variations at distinct scales. Through systematically incorporating the measurements of the variations provided above, our MSA model can faithfully predict the quality of images generated using different DIBR technologies. Results of experiments demonstrate that the proposed blind MSA model has delivered noticeably better performance than state-of-the-art full-and no-reference IQA methods.