降质中子照相图像清晰化及其质量度量方法

Clarification of Degraded Neutron Radiographic Images and Its Quality Metric Method

  • 摘要: 中子照相,也叫中子成像,是一种重要的射线无损检测技术。中子成像数据质量会受到准直比,样品与探测器间距离,散射中子,中子通量,γ射线、快中子等高能光子或粒子对CCD/CMOS相机芯片的干扰等因素影响。主要表现为高斯噪声、泊松噪声、几何不锐度(模糊)和白斑噪声等图像失真,尤其在中子通量受限的小型中子照相系统上愈发严重。为此,本文研究了中子照相图像的多种降质模型,构建了基于真实中子照相图像的多重失真数据集,依据深度学习生成对抗网络模型,设计了基于注意力机制的图像清晰化复原网络,通过端到端的训练,实现了对真实中子照相图像多重失真的有效抑制。同时,鉴于自然图像与中子照相图像的成像机理与失真类型的迥异,进一步设计了针对中子照相失真类型的图像无参考质量度量方案。由30组研究人员对不同复原方案效果的主观打分结果可知,本文所提出的图像清晰化方案在主观评价上取得了最好的表现力。同时,基于本文所提出的图像质量客观评价方法进行定量分析可知,本文复原方案较其他深度学习和传统图像复原方法在质量分数上均有超过10%的提升,这从侧面验证了本文复原方法的有效性。

     

    Abstract: Neutron radiography, also called neutron imaging, is a significant radiographic non-destructive testing (NDT) technology. In the process of neutron imaging, electronic equipment, space fluctuation of neutrons, collimator structure, high-energy particle irradiation imaging detector, and other factors can introduce different degrees of degradation on the neutron radiographic images, mainly in the form of Gaussian noise, Poisson noise, geometric unsharpness (blur), white spot noise, and other image distortions, especially in compact neutron radiography systems with limited neutron flux. Most of the existing distortion suppression algorithms for neutron radiographic images require some prior information on distortion, such as noise intensity and blur intensity. Moreover, the distortion-suppression effect depends greatly on the estimation accuracy of the distortion parameters. However, the distortion model of neutron radiographic images contains a variety of mixed noise and blurring. Suppressing some single distortion may introduce or aggravate other kinds of distortions. Therefore, it is difficult to effectively improve the image quality with a single distortion-suppression scheme. In order to solve this issue, the multiple-degradation models of neutron radiographic images were first analyzed. Then, a large-scale image distortion dataset consistent with the real distortion types of neutron radiography was constructed, including different levels of Gaussian noise, Poisson noise, white spot noise, and Gaussian blur. A novel image restoration network based on the generative adversarial network (GAN) and coordinate attention mechanism was designed. Through end-to-end training, multiple distortions of real neutron radiographic images can be effectively suppressed by the proposed method. Moreover, because of the different imaging mechanisms and distortion types of natural images and neutron radiographic images, a no-reference image quality assessment scheme was further proposed for neutron radiographic images in this paper. A series of experiments on the real neutron radiographic images show that the proposed restoration method achieves good performance in the subjective evaluation. Meanwhile, the objective quality assessment method also verifies the effectiveness of the proposed method. Specifically, according to the subjective scores of 30 groups of researchers on the effects of different restoration schemes, the proposed image restoration scheme achieves the best performance in subjective evaluation. At the same time, based on the quantitative analysis of the objective image quality assessment method proposed in this paper, it can be seen that the quality score of the proposed restoration scheme increases by more than 10% compared with other deep learning and traditional image restoration methods, thus demonstrating the effectiveness of the proposed restoration and quality assessment for the compact neutron radiography system.

     

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