Determination of optimal binary defocusing based on digital correlation for fringe projection profilometry
Determination of optimal binary defocusing based on digital correlation for fringe projection profilometry
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DOI：
10.1016/j.ijleo.2022.170263
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发表时间：
2022-11
期刊：
影响因子：
3.1
通讯作者：
X. Kang;Zhuoyi Yin;Shuai Dong;Xiaoyuan He
中科院分区：
文献类型：
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作者：
X. Kang;Zhuoyi Yin;Shuai Dong;Xiaoyuan He
在条纹投影轮廓术（FPP）中，由于投影仪的伽马效应，投影条纹的非正弦性会引起相位测量误差。为了解决这个问题，近年来已经引入了二进制散焦技术，然而难以以高灵敏度和高精度定量地确定适当的散焦量。提出了一种基于数字相关的确定最佳散焦量的新方法，旨在从投影仪散焦的二值结构条纹图中获得正弦条纹。首先，从捕获的二元散焦条纹图中选择包含多个条纹的窗口，该窗口投影到校准板或被测物体表面的平坦部分上。然后计算所选窗口与其在垂直于条纹方向上的二阶微分之间的相关系数。由于正弦波的二阶微分仍然是正弦的，所以最大相关系数应该对应于二进制散焦条纹的最佳正弦性。因此，通过在使投影仪散焦的同时找到最大相关系数，可以相应地确定最佳二进制散焦水平。该方法的特点之一是在实际测量中只需一个条纹窗即可判断离焦量大小，从而提高了三维测量的速度。此外，该方法对条纹间距没有要求，适用于任何空间频率的条纹。数值仿真和实验结果均表明了该方法的有效性和高精度。
In fringe projection profilometry (FPP), non-sinusoidal projected fringes due to the gamma effect of a projector will cause phase measurement errors. To solve this problem, a binary defocusing technique has been introduced in recent years, while it is difficult to determine an appropriate amount of defocus quantitatively with high sensitivity and high accuracy. In this paper, a novel approach based on digital correlation is proposed to determine an optimal amount of defocus, aiming to get sinusoidal fringes from a binary-structured fringe pattern with projector defocusing. Firstly, a window containing multiple fringes is selected from the captured binary defocusing fringe pattern projected onto a calibration plate or a flat part of the surface of the object being measured. Then calculate the correlation coefficient between the selected window and its second-order differential in the direction perpendicular to the fringe. Since the second-order differential of a sinusoidal wave remains still sinusoidal, the maximum correlation coefficient should correspond to the optimal sinusoidality of the binary defocusing fringe. Therefore, by finding the maximum correlation coefficient while defocusing the projector, the optimal binary defocusing level can be determined accordingly. One of the characteristics of the proposed method is that only one fringe window is required to judge the defocus level in practical measurement, which may speed up 3D measurement. In addition, the proposed method has no requirements for fringe pitch and is applicable to fringes of any spatial frequency. Both numerical simulations and experimental results have been demonstrated to exhibit the validity and high accuracy of the proposed method.