基于数字图像边缘信息的自动对焦算法研究

基于数字图像的自动对焦算法有广泛的应用。提出了一种新的自动对焦算法，该算法通过一最小各向同性小波滤波器在对焦图像序列进行滤波，得到了一边缘特征图像序列，再以能量目标函数为准则，从这些边缘特征图像序列中，选出最佳对焦图像，从而确定精确对焦的位置。实验证明了该算法效果好于方差函数对焦算法。     

ISAR运动补偿聚焦方法的改进

运动补偿是ＩＳＡＲ成像中的关键，。通常分组、精补偿两步进行。粗补偿是回波包络的粗略对齐，而精补偿则是寻找一个相位参考进行回波相位的精细调整，通常称为聚焦。本文提出了两种改进的聚焦法，即加权多特显点综合法和改进的散射重心跟踪法，并与弧立点法作了分析比较，最后利用雷达外扬实测飞机数据比较了它们的成像结果。     

A texture-analysis-based design method for self-adaptive focus criterion function

Autofocusing (AF) criterion functions are critical to the performance of a passive autofocusing system in automatic video microscopy. Most of the autofocusing criterion functions proposed are dependent on the imaging system and image captured by the objective being focused or ranged. This dependence destabilizes the performance of the system when the criterion functions are applied to objectives with different characteristics. In this paper, a new design method for autofocusing criterion functions is introduced. This method enables the system to have the ability to tell the texture directional information of the objective. Based on this information, the optimal focus criterion function specific to one texture direction is designed, voiding blindly using autofocusing functions which cannot perform well when applied to the certain surface and can even lead to failure of the whole process. In this way, we improved the self-adaptability, robustness, reliability and focusing accuracy of the algorithm. First, the grey-level co-occurrence matrices of real-time images are calculated in four directions. Next, the contrast values of the four matrices are computed and then compared. The result reflects the directional information of the measured objective surfaces. Finally, with the directional information, an adaptive criterion function is constructed. To demonstrate the effectiveness of the new focus algorithm, we conducted experiments on different texture surfaces and compared the results with those obtained by existing algorithms. The proposed algorithm excellently performs with different measured objectives.     

空间相机相关法实时检焦技术研究

自动检调焦技术是保证空间相机拍摄出高质量图像的重要技术手段，本文介绍了一种自准直法实时检焦系统。该系统用两块小口径五棱镜代替其他空间相机常用的大平面反射镜，用半导体激光器做光源，用CCD作为光电转换器件，通过测量两光斑在CCD上的移动量，从而计算出离焦量。本文采用相关法处理数据，并通过合理选取阈值和数据拟和技术，实现了亚像素测量精度。该系统具有结构紧凑，稳定性好等特点，实验结果表明检焦分辨率≤10μm。     

Optical microscopy with flexible axial capabilities using a vari‐focus liquid lens

The axial imaging range of optical microscopy is restricted by its fixed working plane and limited depth of field. In this paper, the axial capabilities of an off‐the‐shelf microscope is improved by inserting a liquid lens, which can be controlled by a driving electrical voltage, into the optical path of the microscope. First, the numerical formulas of the working distance and the magnification with the variation of the focus of the liquid lens are inferred using a ray tracing method and conclusion is obtained that the best position for inserting a liquid lens with consistent magnification is the aperture plane and the rear focal plane of the objective lens. Second, with the liquid lens embedded in the microscope, the numerical relationship between the magnification and the working distance of the proposed flexible‐axial‐capability microscope and the liquid lens driving voltage is calibrated and fitted using the inferred numerical formulas. Third, techniques including autofocus, extending depth of field and three‐dimensional imaging are researched and applied, improving the designed microscope to not only flexibly control its working distance, but also to extend the depth of field near the variable working plane. Experiments show that the presented flexible‐axial‐capability microscope has a long working distance range of 8 mm, and by calibrating the magnification curve within the working distance range, samples can be observed and measured precisely. The depth of field can be extended to 400 μm from the variable working plane and is 20 times that of the off‐the‐shelf microscope.     

Digital holographic microscopy and focusing methods based on image sharpness

Digital holographic microscope allows imaging of opaque and transparent specimens without staining. A digitally recorded hologram must be reconstructed numerically at the actual depth of the object to obtain a focused image. We have developed a high‐resolution digital holographic microscope for imaging amplitude and phase objects with autofocusing capability. If the actual depth of an object is not known a priori, it is estimated by comparing the sharpness of several reconstructions at different distances, which is very demanding in means of computational power when the recorded hologram is large. In this paper, we present 11 different sharpness metrics for estimating the actual focus depths of objects. The speed performance of focusing is discussed, and a scaling technique is introduced where the speed of autofocusing increases on the order of square of the scale ratio. We measured the performance of scaling on computer‐generated holograms and on recorded holograms of a biological sample. We show that simulations are in good agreement with the experimental results.     

Self-calibration method for vision-guided cell micromanipulation systems

A new self-calibration method for a piezoelectric actuator-based vision-guided cell micromanipulation system is proposed. This method consolidates all the system parameters' uncertainties into a matrix instead of classifying into intrinsic and extrinsic. The position difference of the micromanipulator tip in the image plane between the measured and estimated output which is based on estimations of relevant parameters is assumed to be caused by the matrix. This matrix is estimated by means of collecting several pairs of known input and the corresponding output differences. Matrix standard deviation and gray-value based matching are applied to identify the output differences. Biological contamination is reduced since a calibration template is not required. This self-calibration is particularly suitable for cell micromanipulation systems where the micromanipulator is frequently dismounted and mounted.     

影响球面激光直写线宽均匀度的关键技术

为提高球面激光直写图形线宽均匀度,提出了球面激光直写四轴同心结构和同心扫描光学系统的方案。这种方案使得激光束经水平轴、垂直轴、光轴和工件中心轴相交于球心,经球心反射镜反射到球面工件表面上,形成激光曝光光斑。采用微小离焦探测和复合闭环控制的自动调焦技术与计算机并行工作的控制方法,确保了球面工件以垂直轴为轴心沿水平方向精密匀速旋转;激光笔绕水平轴以俯仰弧形轨迹移动且精准定位;激光束经写入物镜和调焦系统始终以圆形光点聚焦在球面上,实现了对球面任意纬度连续激光直写线条精度的可靠控制。原子力显微镜检测分析结果表明,在球面上激光直写出约3μm宽线条,线宽均匀度10%左右。     

二维图像测量机系统的研究

本文在分析了传统二维坐标测量系统的优缺点的基础上,提出了一种新的基于CCD图像技术的二维坐标测量系统－二维图像测量机。该系统的读数部分、调焦与瞄准部分均采用CCD图像技术。文中给出了新系统的结构、原理、研究了系统实现的关键技术,并对新系统进行了实验研究与比对,最后,分析了系统的精度。