【作者】 赵烈烽；

【导师】 冯华君； 刘旭； 徐之海；

【作者基本信息】 浙江大学 ， 光学工程， 2008， 博士

【摘要】 环带成像系统是全景成像系统的一种,在监视、监控、机器视觉等领域具有广阔的应用前景。全景成像系统通常可理解为是一种能把360°方位角空域内的景物投影到二维成像平面上的光学系统。不同于传统的三维透视投影法,环带成像系统采用了从柱面到平面的投影,因此具有不同的成像特性。环带成像系统的核心是环带镜头。本论文对环带镜头的特性、物像关系进行了深入的研究,提出了环带镜头的光瞳像差理论和环带镜头的双目立体视觉理论。在此基础上,本文还提出了一种基于液晶快门技术的高分辨环带成像系统,其视场超过水平面,并顺利完成了系统的设计、加工、装校和测试。文中对液晶快门进行了定性和定量的讨论,提出了双层的液晶盒结构,并将液晶快门安装在环带镜头的镜间。制作了带有镜间液晶快门和不带液晶快门的两款环带镜头,分辨率和MTF的对比测试结果证明加装液晶快门对成像质量降低的影响在本系统中可以忽略。本文对环带镜头中加装的液晶快门不能100%阻挡入射光而带来的拖影问题进行了深入的分析,并用遮阳机构解决了太阳光直射问题,用数字图像处理的方法进行了拖影补偿。对于视场超过水平面的环带图像,结合物像关系的分析,给出了图像展开的基准,并用实验进行了验证。论文具体研究内容如下:第一章介绍了课题研究背景,指出环带镜头可为实现全向和实时信息获取提供解决方法,对比了国内外现有的非凝视型和凝视型大视场成像技术,确定了本文的主要研究内容。第二章对PAL镜的光学特性进行了深入分析,指出了其像面照度优于一般全景镜头的特点。深入讨论了环带镜头的光瞳像差理论,建立了PAL镜的数学模型,提出了用多项式预报光阑球差的快速光线追迹法。第三章分析了常见的四种实现“非相似”成像的像高表达式,讨论了它们在环带成像系统中的像面放大率及畸变量。提出了利用满足f-θ投影关系的环带镜头实现双目立体视觉的理论,并结合管道内窥系统,提出了利用帧间图像测量物点距离,获取管道内径的方法,用环带镜头设计了一款管道内壁检测系统,给出了管道内径测量的实例和误差分析。第四章提出了一种将液晶盒作为光学快门的高分辨环带成像系统。为了考察液晶对成像质量的影响,设计并制作了带镜间液晶快门和不带液晶快门的两款高分辨、视场超水平面的环带镜头。对于成像系统读出的图像进行了预处理,重点讨论了如何补偿液晶不能完全关门所带来像面拖影。最后结合第三章分析的物像关系理论,研究了超水平面环带成像系统图像展开算法的特点,提出为了保证子午和弧矢方向放大率一致,图像展开的基准应为90°视场角所对应像面上的圆环,并给出了实验结果。第五章扭曲向列型液晶进行了定性的讨论和定量的分析,分析的结果可用于指导环带镜头中的液晶快关设计。最后给出了双层液晶盒结构的液晶快门,并给出了透过率的测试结果。第六章讨论了环带镜头的测试方法,包括分辨率测试和MTF测试。测试了两款环带镜头的光学性能,分析了测试系统中各组件对测试结果的影响,特别是CCD离散器件采样的影响。测试结果显示加装液晶快门并不会导致成像质量的明显下降,两款环带镜头的测试结果均符合我们的设计要求。最后一章对本文进行了总结,并提出了展望。更多还原

【Abstract】 The annular lens imaging system, which is one kind of panoramic imaging systems, has broad application future in the areas of inspection, security, robot’s vision, and et al. The panoramic imaging system are generally understood as a system, which can project the 360°surrounding objects into a two dimensional image plane. The annular lens imaging system has unique characteristics as it is using the Flat Cylinder Perspective (FCP) instead of traditional Central Point Perspective (CPP).The critical element of an annular lens imaging system is the annular lens. This thesis has detailed the characteristics of the annular lens and the object-image relation; proposed the pupil abberation theory and the dual-lens stereoscopic vision theory of the annular lens. According to that theories, we have designed manufactured, fabricated and tested an annular lens with high resolving power and large field of view, which is exceeding the horizontal line, based on the liquid crystal shutter (LCS) technique. This thesis has discussed the LCS both qualitatively and quantitatively; proposed the dual-layer structure LCS, and fixed the LCS inside the annular lens. We have built two types of annular lenses, one of which is equipped with a LCS and the other is not, and the results of resolving power and MTF tests shows the image degradation effect of the adding LCS is neglectable in our system.This thesis detailed the smears problems in the image plane caused by that the LCS cannot block the incident light to 100%, and also proposed the shading mechanical method to solve the direct sun shine problem and the image processing method to compensate the smears. For the annular image exceeding the horizontal line, we proposed the base line for the image transformation to keep the magnification ratio of tangential and sagittal directions. The detailed research contents are listed as follow.ChapterⅠintroduced the research background, pointed out that the annular lens technique can fulfil the requirement of realtime omnidirectional inspection. We compared the existing un-staring and staring panoramic imaging techniques, and determined the research aims.ChapterⅡanalyzed the optical characteristics of the PAL lens in detail, pointed out that the illumination on the image plane is more uniform than the other panoramic lenses. The sphere abberation of the entrance pupil of the annular lens was studied thoroughly, and the mathematic model of the PAL lens was made. A fast ray tracing method using polynomial abberation prediction was proposed.ChapterⅢanalyzed four image height expressions with not-resemble imaging characteristics, discussed their magnifying ratios and distortions. We proposed the dual-lens stereoscopic vision method using the annular lens using the f-θrelationship. When applied that method to the endoscopy of the pipes and bores, we proposed the method to measure the distance of the objects, i.e. the radius of the pipes, using the frames taken by a single annular lens. An bore endoscopy experiment system using the annular lens was made and the caused error was discussed.ChapterⅣproposed a design of an annular lens with high resolving power based on the LCS as the optical shutter. In order to find the image degradation caused by the LCS, we designed and fabricated two super hemisphere annular lens with high resolving power, one of which is equipped with a LCS and the other is not. We pretreated the readout images, and the methods to compensate the smears on the image plane caused by the LCS was discussed emphatically. Combining the object-image relation discussed in ChapterⅢ, we discussed the characteristics of annular image transformation, pointed out that in order to keep the tangential and sagittal magnifying ratios same, one should use the circle image corresponding to the field of angle of 90°as the base line. A corresponding experiment was given.ChapterⅤdiscussed the twisted nematic LCS both qualitatively and quantitatively. The results should guide the design of LCS. We designed a double-layer LCS, and tested the transmission of the LCS.ChapterⅥdiscussed the annular lens testing methods, including the resolving power and MTF tests. We tested the two types of lenses and compared the results, analyzed the effects of the auxiliary equipment, especially the CCD discrete sampling period. It shows that the built in LCS has no evident image quality degradation. Both testing results were fulfill our design aims.The last chapter summarized the full thesis and proposed the future plan.更多还原