Image quality is important not only for the viewing experience, but also for the performance of image processing algorithms. Image quality assessment (IQA) has been a topic of intense research in the fields of image processing and computer vision. In this paper, we first analyze the factors that affect twodimensional (2D) and three-dimensional (3D) image quality, and then provide an up-to-date overview on IQA for each main factor. The main factors that affect 2D image quality are fidelity and aesthetics. Another main factor that affects stereoscopic 3D image quality is visual comfort. We also describe the IQA databases and give the experimental results on representative IQA metrics. Finally, we discuss the challenges for IQA, including the influence of different factors on each other, the performance of IQA metrics in real applications, and the combination of quality assessment, restoration, and enhancement. INDEX TERMS Image quality assessment, image aesthetics assessment, visual comfort, and image quality enhancement.

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Selective capture of ethane (C2H6) from ethylene (C2H4) mixtures is critical for the direct production of polymer-grade ethylene. However, it remains a great challenge to design industrially potential porous materials with satisfied capacity and separation selectivity. Herein, we reported a series of low cost and easy-attainable biomass carbon-derived activated carbons (ACs) by alkali activation that show remarkable C2H6/C2H4 separation performance. A systematic research study was conducted to study the effects of different carbon sources, different activators, and activation temperatures on their separation performance of the corresponding afforded ACs. The C2H6 adsorption capacity (6.36 mmol g–1) and the C2H6/C2H4 (1/1 v/v) selectivity (2.6) of alkali-treated coconut shell ACs CAC-X-Y (X represents the activated temperature, Y represents the ratio of KOH/C) are superior to those of the most reported ethane-selective materials, and 99.9% purity of C2H4 could be directly obtained from C2H6/C2H4 mixtures. It is noteworthy that the cost of CAC-derived ACs is estimated to be only around $20 per kg, demonstrating their great industrial potential for gas separations.

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