Error-CompensatingFive-SamplePhase-Shifting Algorithm Based on Phase-Shift Error Estimation

A new error compensating five sample phase shifting algorithm which is insensitive to phase shift error is proposed to retrieve the phase distribution of a fringe pattern. It includes two steps. First, the linear phase shift error is estimated using four sample images. Then, the phase distribution is calculated with error corrected by using the phase shift error estimated in the first step. As the equations of error estimation and phase calculation are simple, this new algorithm is practical as well as effective. Computer simulations were carried out to verify the effectiveness of the algorithm. Results of two other well known error compensating algorithms are also presented, which show the new algorithm is the least sensitive to phase shift error.

Erratum and Note: Measurement of Zeeman Shift of Cesium Atoms Using an Optical Nanofiber [Chin. Phys. Lett. 35(2018) 083201]

Our recent article (Chin. Phys. Lett. 35 (2018)083201) measured the Zeeman shift of cesium atoms using an optical nanofiber. Before our work, Watkins et al.(Ref.[17] in our article) had demonstrated the Zeeman shift also using an optical nanofiber in rubidium atoms. Watkins et al. reported on the observation

Nonlinear effect of the structured light profilometry in the phase-shifting method and error correction

Digital structured light （SL） profilometry is increasingly used in three-dimensional （3D） measurement technology. However, the nonlinearity of the off-the-shelf projectors and cameras seriously reduces the measurement accuracy. In this paper, first, we review the nonlinear effects of the projector-camera system in the phase-shifting structured light depth measurement method. We show that high order harmonic wave components lead to phase error in the phase-shifting method. Then a practical method based on frequency domain filtering is proposed for nonlinear error reduction. By using this method, the nonlinear calibration of the SL system is not required. Moreover, both the nonlinear effects of the projector and the camera can be effectively reduced. The simulations and experiments have verified our nonlinear correction method.

Single-Shot Measurement of Transient Phase Shift Induced by Laser Wake

Based on the frequency-to-time mapping relation of the linearly chirped pulse, the temporal phase shift induced by a laser-excited wake in a helium gas jet is measured using a chirped-pulse spectral interferometry with ～ 140 fs resolution over a temporal region of I ps in a single shot. In this measurement, the image of the wake is obtained with one-dimensional spatial resolution and temporal resolution limited only by the bandwidth and chirp of the pulse. The ＇bubbles＇ feature of the wake structure, along with multiple wakes excited by the main lobe and the side lobe of a laser focal-spot, is captured simultaneously.

Measurement of Zeeman Shift of Cesium Atoms Using an Optical Nanofiber

Nanofibers have many promising applications because of their advantages of high power density and ultralow saturated light intensity. We present here a Zeeman shift of the Doppler-broadened cesium D2 transition using a tapered optical nanofiber in the presence of a magnetic field. When a weak magnetic field is parallel to the propagating light in the nanofiber, the Zeeman shift rates for different circularly polarized spectra are observed.For the ＋component, the typical linear Zeeman shift rates of = 3 and = 4 ground-state cesium atoms are measured to be 3.10（±0.19） MHz/G and 3.91（±0.16） MHz/G. For the -component, the values are measured to be-2.81（±0.25） MHz/G, and-0.78（±0.28） MHz/G. The Zeeman shift using the tapered nanofiber can help to develop magnetometers to measure the magnetic field at the narrow local region and the dispersive signal to lock laser frequency.

Comparison of methods for turbulence Doppler frequency shift calculation in Doppler reflectometer

The Doppler reflectometer(DR),a powerful diagnostic for the plasma perpendicular velocity(u⊥)and turbulence measurement,has been widely used in various fusion devices.Many efforts have been put into extracting the Doppler shift from the DR signal.There are several commonly used methods for Doppler shift extraction,such as the phase derivative,the center of gravity,and symmetric fitting(SFIT).However,the strong zero-order reflection component around 0 kHz may interfere with the calculation of the Doppler shift.To avoid the influence of the zerofrequency peak,the asymmetric fitting(AFIT)method was designed to calculate the Doppler shift.Nevertheless,the AFIT method may lead to an unacceptable error when the Doppler shift is relatively small compared to the half width at half maximum(HWHM).Therefore,an improved method,which can remove the zero-frequency peak and fit the remaining Doppler peak with a Gaussian function,is devised to extract the Doppler shift.This method can still work reliably whether the HWHM is larger than the Doppler shift or not.

An Improved Calibration Method of Grating Projection Measurement System

In the traditional fringe projection profilometry system,the projector and the camera light center are both spatially virtual points.The spatial position relationships specified in the model are not easy to obtain,leading to inaccurate system parameters and affectingmeasurement accuracy.This paper proposes a method for solving the system parameters of the fringe projection profilometry system,and the spatial position of the camera and projector can be adjusted in accordance with the obtained calibration parameters.The steps are as follows:First,in accordance with the conversion relationship of the coordinate system in the calibration process,the calculation formula of the vertical distance from the camera light center to the reference plane and the calculation formula of the distance between the projector and the camera light center are given respectively.Secondly,according to the projector calibration principle,the position of the projector light axis perpendicular to the reference plane is gained by comparing the parallel relationship between the reference plane coordinate system and the projector coordinate system’s Z-axis.Then,in order to fulfill the position restriction that the line between the projector light center and the camera light center must be parallel to the reference plane,the camera’s spatial location is adjusted so that the vertical distance between it and the reference plane tends to that between the projector light center and the reference plane.And finally,the three-dimensional(3D)reconstruction of the target object can be finished using the phase height model’s system parameters once the aforementioned position limitations are put into practice.Experimental results demonstrate that the method improves the measurement accuracy,and verifies that it is effective and available in 3D shape measurement.

A NEW ALGORITHM FOR ELIMINATING PHASE-SHIFT ERROR IN PHASE SHIFTING INTERFEROMETRY

The effect of phaseshift error in phase shifting interferometry is investigated. A new algorithm with two sets of 4 samples for eliminating phase shift error is presented. The computer simulation and experiment result show that the phase shift offset should be π when the algorithm is used, and this algorithm has gotten better result than the original 4 sample algorithm.

基于主成分分析和VU分解法的两步随机相移算法

为了平衡相位计算的精度和速度,大量的两步随机相移算法发展起来。提出了一种基于主成分分析和VU分解法的快速、高精度两步随机相移算法。首先,采用两步主成分分析法对经过滤波的两幅相移干涉图进行计算求出迭代初始相位;然后,利用没有滤波的两幅相移干涉图进行VU分解、迭代求出最终相位。通过模拟和实验结果对比表明:与四种性能良好的两步随机相移算法相比,对于不同的条纹类型、噪声、相移值及条纹数量,提出的算法综合性能最好,其精度最高,有效相移范围和有效条纹数量范围最大,当干涉图像素数为401 pixel×401 pixel时,提出的算法仅比格兰-施密特正交化法和两步主成分分析法多花费0.035 s。在理想情况下,提出的算法可以得到完全正确的结果。如果需要得到较高精度,最好能够提前抑制噪声,同时设置相移值远离0和π,条纹数量大于2。主成分分析和VU分解法无需滤波,花费近似非迭代算法的时间获得迭代算法的精度,其打破了迭代算法花费时间较多的限制,适合高精度光学在线检测,有广泛的发展前景。

基于多频相移的相位偏折测量透明物体表面三维形貌

光学三维测量中的相位偏折测量术以其快速、高精度、稳定抗干扰的优点,在光学表面测量、快速检测等领域得到广泛应用。透明物体因其上下表面的折射和反射,导致相机采集到不同表面反射叠加的混合条纹,传统的相位偏折测量术难以对其进行有效的三维测量。为解决该问题,文中提出一种基于多频相移的相位偏折法测量透明物体的表面三维形貌。首先,显示屏显示多种不同频率与多步相移结合的正弦条纹,从另外一个角度相机采集物体表面反射的混合条纹。然后,利用最小二乘法迭代将混合条纹进行分离,得到上下表面折叠相位并展开。接着,通过梯度标定确定相位与梯度的关系,根据梯度积分恢复透明物体表面的三维形貌。最后,实验证明所提方法能够有效实现混合条纹的分离,实测透明玻璃板上表面的平均误差从32.4μm减少到5.1μm,结果验证了混合条纹分离方法的有效性,提升了透明物体表面三维形貌测量精度。与已有方法相比,文中方法可以有效避免初始相位值偏差较大带来的影响,缩短计算时间,适用于不同形状透明物体表面三维形貌的测量。

自动选择跟踪窗尺度的Mean-Shift算法

实用的跟踪系统要求能实时地适应运动目标的外观变化,尺度固定不变的跟踪窗口不能有效地跟踪存在明显尺度变化的目标。本文将多尺度图像的信息量度量方法引入到运动目标跟踪中,提出了一种跟踪窗口自动更新算法,并用此算法改进了基于颜色直方图的Mean-Shift跟踪方案。实验结果表明,改进的跟踪算法对尺寸逐渐减小和逐渐增大的目标都能自动选择合适的跟踪窗口大小。

车身漆面缺陷的自动检测与定位方法

针对目前国内汽车制造业中面漆后车身表面缺陷难以非接触高精度检测,得不到缺陷确切位置等问题,这里提出了一种结合相位测量偏折术与双目测距原理的车身漆面缺陷检测定位方法。首先采用四步相移法提取车身反射图像相位,运用格雷码进行相位解包裹,再通过判断局部相位突变来提取缺陷;建立缺陷池并通过过滤器去除伪缺陷得到真实缺陷;基于双目测距原理,对检测出的缺陷,取其形状中心再得到具体位置坐标。实验结果表明,该缺陷检测方法能够自动,准确,稳定地检测漆面缺陷;双目测距法能准确地得到缺陷的具体位置,可为后续实现自动打磨提供可靠数据来源。

激光共焦干涉面形快速高精度自动测量

针对传统球面面形干涉测量中手动调整被测件姿态精度低、速度慢的问题,提出了激光共焦干涉面形快速高精度自动测量方法。该方法通过共焦精密定焦技术实现了对被测件共焦位置的高精度轴向定位;通过五维自动调整架对被测件进行姿态调整,实现了被测件的高精度横向定位;通过Zernike拟合对被测件进行精调以减小离焦误差和倾斜误差,实现了对干涉面形的零条纹调整。最终实现了激光共焦干涉面形自动测量。构建了激光共焦干涉面形测量系统,实验表明:该方法的面形测量结果与Zygo干涉仪的测量结果相差0.000 6λ,重复测量精度可达0.001 9λ,平均单次干涉面形测量时间为16.5 s,与手动调整至零条纹相比测量效率提高了1.56倍。该方法为干涉面形的快速高精度测量提供了一种有效的手段。

双环Mean Shift视频跟踪算法

针对传统均值漂移跟踪算法在目标特征提取、模板匹配度量和带宽固定方面存在缺陷,提出一种双环Mean Shift视频跟踪算法.该算法采用万向椭圆的特征提取方式,能更有效地抑制背景信息影响,较好地提高目标模型质量.引入双环描述因子能突出目标本身特征权重,改善图像匹配峰值特性,并通过双环之间的关系自适应地更新核函数的带宽.仿真实验结果表明该算法在目标具有明显尺度变化、姿态扭曲和部分遮挡的情况下,可以获得准确和鲁棒的跟踪效果.

目标窗口尺寸自适应变化的Mean-Shift跟踪算法

传统的窗宽尺寸固定不变的Mean-Shift跟踪算法不能实时地适应目标尺寸大小的变化。将多尺度空间理论与Kalman滤波器相结合,利用Kalman滤波器对尺寸变化的目标面积比例进行预测,用多尺度空间理论中的目标信息量度量方法求出前后相邻两帧的目标特征信息比,将其作为Kalman滤波器的观察值对目标面积比例进行修正,然后与Mean-Shift算法结合起来对目标进行跟踪。实验结果表明,改进的跟踪算法对尺度逐渐变大和变小的目标都能连续自动地选择合适大小的跟踪窗口。

表面应力敏感膜传感图像的振动校正算法

表面应力敏感膜传感系统在风洞中的不稳定振动给测量结果带来较大的误差,提出了一种自标定方法对表面应力敏感膜传感图像进行振动校正,消除不稳定平台振动的影响,减少测量误差。首先通过原始传感图像的互相关获得包含振动和有效信息的初始位移,然后通过大津阈值法和形态学获得参考区掩码,最后使用透视变换原理和最小二乘法还原整个振动平面并进行振动校正。方法将敏感膜传感图像的子区作为特征点参与计算,实现了振动的自标定校正,能使传感系统在不稳定平台也能进行高精度测量。通过高速列车实验验证了该方法的有效性和实用性,结果显示该方法相比其它传统方法精度更高,鲁棒性更好,产生了良好时空分辨率图像,在50m/s的来流中,将振动平均误差降低了98%。

一种改进的Mean Shift跟踪算法

本文主要针对经典的Mean Shift跟踪算法均匀剖分整个颜色空间造成许多空的直方图区间以及不能准确表达目标颜色分布的缺点,提出了一种改进算法．该改进算法首先对目标的颜色进行聚类分析,根据聚类结果通过矩阵分解和正交变换自适应地剖分目标的颜色空间从而确定对虑于每一聚类的子空间．在此基础上定义了一种新的颜色模型,该模型统计落入每一颜色子空间的像素的加权个数并用高斯分布建模每一个子空间的颜色分布,并推导了一种相似性度量来比较目标和候选目标的颜色模型之间的相似程度．最后基于该颜色模型提出了改进算法．实验表明,基于该颜色模型的改进算法比经典的Mean Shift算法具有更好的性能,而跟踪时间与经典算法大致相同．

具有管状基准照明系统的斐索平面相移式干涉仪

本文利用具有F-P标准具的管状基准的等倾干涉原理,设计了两种具有管状基准照明系统的斐索平面相移式干涉仪。这两种干涉仪通过气泵来增压或者减压管状基准主体内的气压,从而改变管状基准内介质折射率,进一步改变参考光和测量光的光程差,以此实现相移技术,完成对平晶平面度的测量。两种干涉仪分为立式和卧式,分别对应不同使用场景。相较于等倾干涉仪测量系统,本文设计的干涉仪系统改善了热交换的环境,测量点数增多,可给出被测平晶平面地形图;相较于利用压电陶瓷实现相移技术的菲索平面干涉仪,本文设计的干涉仪系统在测量中没有机械运动的移相,且造价更低,安全性更高。

基于离焦度解包裹的结构光三维测量方法

基于结构光相位解包裹三维测量方法由于其精度较高而有广泛应用,但由于相位在超出2π时会被折叠,导致传统的结构光三维重建时需要相位解包裹。相位测量轮廓术在不连续深度处的解包裹相位较为复杂。当被测物体表面存在较大的深度差或者是测量多个平面时,由于包裹相位范围为[0,2π],在不连续处计算的相位差中存在折叠了多个2π的问题,导致解包裹失效。相位测量轮廓术在此时无准确表达物体位置信息。针对此问题,提出了一种基于离焦度解包裹的结构光三维测量方法,采用24步相移法获取包裹相位,通过时间散焦分析法确定包裹相位2π的个数来辅助进行解包裹计算。搭建了相应平台进行了实验,对所提方法进行验证。实验表明,方法较好的解决了相位测量轮廓术在深度落差较大时不能准确表达物体位置的问题,该方法可以用于获得深度落差较大场景的深度信息以及细节信息。

基于结构光的三维重建研究方法

随着测量技术的不断发展,快速且精准地获取物体三维信息成为研究的热点。传统测量方法存在精度有限且需要在被测物体上添加传感器的问题。因此,提出了根据正弦条纹结构光投影时条纹产生的形变,采用相依轮廓术对目标物的三维重建。在提出的模型中,实验结果表明,在重建精度和测量速度等方面都有着优越的性能。