【作者】 谌雨章；

【导师】 杨克成；

【作者基本信息】 华中科技大学 ， 光学工程， 2012， 博士

【摘要】 激光水下目标成像被广泛应用于海洋、江河及湖泊探测等领域,但是由于存在水体对激光的吸收散射等衰减效应、成像系统的衍射极限、像差畸变以及水下湍流等因素,水下图像存在严重的降质,主要表现在噪声、模糊及低分辨率等方面。近年来已有学者从图像增强、复原入手,改善图像退化,提高图像的清晰度,但效果仍需改进,且分辨率得不到提高,有些算法甚至会降低分辨率。分辨率是评价图像的重要参数,提高水下成像的图像质量,特别是在人眼视觉方面,很大程度上决定于分辨率的提高。因此本论文从图像处理的各个环节入手,研究、提出并实验了大量的图像复原及超分辨率重建算法。本论文首先介绍了水下距离选通激光成像实验系统,给出了详细的实验框图、设备和实验结果；回顾了经典的点扩散模型,分析了异同点并确定建模需求；通过计算到达探测器的三种光分量,考虑距离选通门、光学镜头衍射极限、传感器畸变及水体湍流等因素,建立了基于本课题实验系统的水下成像模型,并计算得到了成像系统的调制传递函数和点扩散函数。为了有效去除噪声对水下图像处理的影响,本论文分析了水下成像过程中引入噪声的各种因素,基于噪声的统计特性提出了基于边缘检测的分块混合滤波图像去噪法,并进行了实验验证了去噪预处理的有效性；分析了使用客观指标评价图像质量的必要性,根据图像复原和超分辨率重建算法的特性,分别给出了相应的客观评价参数,并在后面章节作为图像处理结果的评判标准；建立了图像处理评估系统框图,展示了本论文所有图像处理方法的关系枢纽。在改进图像复原方法的方面,本论文根据成像系统的调制传递函数和点扩散函数,提出了基于建模及边界控制约束的半盲图像复原方法,以线结构光探测实验系统作为平台验证了将该方法的有效性和可行性；作了大量实验将水下距离选通成像图像进行了基于调制传递函数的频率域图像复原以及基于点扩散函数的空间域图像复原,并以客观评价标准来评判复原结果；实验结果验证了预处理去噪对于复原方法的有效性,基于本论文建立的水下距离选通成像模型得到的点扩散函数的半盲图像复原法取得了较好的复原效果。为了提高水下成像图像的分辨率,本论文提出了将超分辨率重建引入水下,从单帧和多帧处理出发,将水下距离选通成像图像序列进行了传统超分辨率重建实验,使用相应的客观评价标准评判重建结果：实验结果验证了预处理去噪对于超分辨率重建方法的有效性,及超分辨率重建引入水下的可行性；根据基于建模的复原方法,提出了基于建模的超分辨率重建方法并作了大量实验,结果表明,基于本论文建立模型得到的点扩散函数的凸集投影超分辨率重建方法取得了较好的复原效果。由于基于成像系统点扩散函数的最佳图像复原和超分辨率重建方法都已实验得到,本论文在贝叶斯框架下,利用图像复原和超分辨率重建的优势及特长,将基于建模的复原和超分辨率重建方法有机结合在一起,并实验验证了混合算法的优越性；通过边缘提取,验证了本论文所提出方法能有效提高水下距离选通成像图像的质量,最后总结并提出了水下成像图像处理的后续工作展望。更多还原

【Abstract】 Underwater imaging is widely used in ocean, river and lake exploration, but it is affected by properties of water and the optics including lenses and sensors. Image restoration methods can help to eliminate the blur caused by absorption and scattering; however, the resolution is still limited or even degraded, and the restoration methods are needed to be improved. Considering all the aspects of image formation, this dissertation studies and proposes various image restoration and super-resolution reconstruction methods.The dissertation introduces the underwater range-gated laser imaging system, gives a detailed block diagram of the experimental equipment and experimental results; reviews and analyzes the similarities and differences of several classic point-spread models which determine the needs of modeling. By calculating the three components of light irradiance reaching the detector, based on linear transmission theory, an underwater imaging model suitable for the range-gated imaging system considering the gated time was established in this study including laser beam propagation affected by absorption and scattering, the effects of underwater turbulence and the diffraction limit of sensors. The model-derived modulation transfer function (MTF) and point spread function (PSF) are applied for the theoretical basis of underwater image processing.The dissertation proposes and tests an edge based hybrid block denoising method and applies it as the preprocessing module before the restoration and super-resolution reconstruction. As there exists no ideal or reference image for underwater imaging system, blind, objective quality metrics are chosen for evaluating the performance of the PSF-based restoration and reconstruction methods respectively.Based on the MTF and PSF derived by the imaging model, PSF-based semi-blind restoration is verified by its performance in a structured light detection system. MTF-based restoration methods in frequency domain and PSF-based restoration methods in time domain are tested by their performance in our underwater range-gated imaging system. Super-resolution reconstruction methods operated by single and multiple frames are introduced in the underwater range-gated imaging system, performances of which show adequate accuracy and feasibility. The PSF-based reconstruction methods in time domain are also tested by their performance in our underwater range-gated imaging system.In order to process the experimental imagery to a best possible level, image restoration and super-resolution reconstruction techniques are combined with the point spread function (PSF) of underwater range-gated imaging system under the maximum a posteriori (MAP) framework, performance of which shows superiority compared to other methods. Edge detection are performed and proved that the restoration and super-resolution reconstruction methods proposed by this dissertation can effectively enhance the resolution and quality of underwater range-gated imaging.更多还原