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题名:
基于图像处理的自动调焦变焦技术研究
作者: 倪军
学位类别: 博士
答辩日期: 2007-06-01
授予单位: 中国科学院光电技术研究所
授予地点: 光电技术研究所
导师: 袁家虎
关键词: 光电目标跟踪 ; 自动调焦 ; 评价函数 ; 变焦镜头 ; 图像质量评价
学位专业: 信号与信息处理
中文摘要: 自动调焦、连续变焦是新一代光电跟踪设备的关键技术,为了改善光电跟踪产品的性能,本文对自动调焦、变焦技术进行了深入研究,包括自动调焦理论与方法,调焦评价函数及算法,调焦窗口规划技术,同时也研究了自动变焦技术。研究的内容与成果有以下几点: 本文深入研究了基于图像处理的自动调焦理论和方法。通过实验,分析了频谱函数、梯度函数和熵函数在自动调焦应用时的性能,讨论了移动目标调焦的特殊性以及它对调焦评价函数曲线的影响,给出了移动目标调焦的前提条件和计算方法。 本文提出一种基于排序梯度和的调焦评价函数。原有的基于梯度算子的评价函数是以所有梯度为统计对象,在目标或背景有变化时,大量的低值梯度对评价函数的单峰性产生影响,易导致调焦失败。该函数以排序在前 位的梯度作为统计对象,计算其梯度和,作为调焦评价函数。实验验证了该函数在目标有一定范围内大小变化时具有良好的调焦评价性能。为了减少大的尖锐噪声对评价曲线的影响,本文又提出一种基于阈值梯度数统计的调焦评价,该算法比较前后帧图像中大于某一动态阈值的梯度数量,得到调焦的方向,通过实验曲线图可以看出该方法可以有良好的准确性和稳定性。 本文通过对连续自动调焦的流程分析,说明了在调焦前对图像做清晰度判断的必要性。通过实验,分析了图像清晰程度与目标边缘锐度的对应关系,提出一种基于边缘法向梯度分布特征的单帧图像清晰度判断算法。该算法以参数的形式把图像的清晰程度反映出来。通过实验证明了该算法对光电跟踪设备的图像有良好的判断性能。通过对当前图像的清晰度判断,减少了自动调焦的误触发。 选取合适的调焦窗口是自动调焦过程中重要的技术。调焦窗口中应包含尽可能多的成像主体,使背景的影响尽可能小。本文根据光电跟踪设备图像的特点,结合目标跟踪技术,提出两种调焦窗口动态规划算法:基于动态阈值质心跟踪调焦窗口算法和自适应相关匹配跟踪调焦窗口算法。质心跟踪窗口规划适合背景简单,目标大小合适的序列图像场合,具有速度快,稳定的特点。相关跟踪窗口规划具有较强的局部抗干扰能力,适合信噪比不高,背景复杂的场合。 本文研究了基于图像处理的连续自动变焦原理,提出连续自动变焦流程。基于图像处理的连续自动变焦技术关键是要准确提取目标的成像大小。实验分析了图像单阈值分割和自适应阈值分割的优缺点。提出基于边缘梯度的阈值分割方法。通过选取边缘过渡区上的灰度作为动态分割阈值。减少了背景起伏的影响和噪声点的影响。 本文设计了一个基于PC机的调焦、变焦实验系统。通过对实物目标和仿真目标的实验。验证了本文研究的自动调焦、变焦技术的准确性、可靠性。
英文摘要: Auto focus is a key technology in new electro-optical tracking and detecting system. In order to improve performance of electro-optical tracking and detecting products, this dissertation fulfilled some important theoretical and technical studies about autofocusing, such as auto focus theories and methods, focus function and algorithm, focus framing technologies, we also developed some effective methods to control zoom-lens automatically. This dissertation achieved a numbers of outcomes. Basic theories and methods of autofocus based on image processing are studied in detail. By some experiments, we analyzed the capability of frequency spectrum function, gradient function and entropy function used in autofocus. We also have studied autofocus methods for moving target, discussed the Characteristics of autofocus for moving target and influence to smoothness of focus measure curve and proposed the precondition for moving target’s autofocus and calculatingly methods . A new autofocus evaluate function based on the sum of order grads is proposed. Traditional function based on grads should calculate all grads in image area. If object or background is changed, the sum of most small value grads would make the lens be drive to wrong position. The new focus function only calculate some grads which sorted ahead, the feasibility of this algorithm was proved by a series of focus experiments when size of object changing in a certainly range. To reduce the disadvantage caused by pulse noises, another function based on the number of grads above threshold is proposed. This function compares the number of grads above a dynamic threshold in current frame image with that in last frame, and gets the direction of autofocus. Curve of experiments result proves this function has excellent veracity and reliability. By analyzing the flow of autofocus, we have concluded that judging current image be in focus or not is necessary before doing autofocus. We proved the corresponding connection between degrees of definition and edge acutance by means of experiments. So, a judgment algorithm based on the edge feature was proposed, which used for judging current image be in focus or not. It can express the degree of definition by math parameters and has good performance in judging the images of sky objects. Appropriate focus window selection is an important factor in the process of autofocus. Most of pixels in focus window should be from object image, thus can reduce the disturbing effect cause by pixel from background. According to the feature of image, using technology of aim tracking for reference, we proposed two schemes about focus window selection: based on tracking object’s center of mass and based on correlation match tracking method. The first method is suitable for situation that background gray scale is smoothly. It has advantages of rapid reaction and steady tracking object. The second method has power capability of anti-disturbance, which suitable for situation that image in low SNR and low contrast. The theory of changing focus based on image processing is studied and the flow of changing focus is proposed. How to get the real size of object in image is the key technology. After discussing the advantage and disadvantage of image segment by single threshold and by adapting threshold, we presented an algorithm of image threshold segment based on edge grads. It use grays located in edge transition region as threshold and reduce the influence caused by background and noise. An autofocus and auto-zoom system based on PC has been designed. After performing a series of autofocus and auto-zoom experiments, we conclude this system has excellent veracity and reliability.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ioe.ac.cn/handle/181551/233
Appears in Collections:光电技术研究所博硕士论文_学位论文

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Recommended Citation:
倪军. 基于图像处理的自动调焦变焦技术研究[D]. 光电技术研究所. 中国科学院光电技术研究所. 2007.
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