Background

Digital image correlation (DIC) method is a non-interference and non-contact full-field optical measurement technology. DIC’s measurement accuracy is largely determined by the image acquisition system and the quality of the speckle pattern.

Objective

Although the optimal speckle pattern has been designed theoretically, the optimization process does not consider the influence of the imaging system. Furthermore, the optimal aperture has not been yield. The objective of this paper is to improve the measurement accuracy through optimization of aperture and speckle pattern.

Methods

In this paper, speckle images with different apertures and different speckle generation parameters were captured, and the corresponding measurement errors were evaluated.

Results

(1) The influence of aperture and the optimization of speckle are independent of each other. The optimal speckle generation parameters (speckle size and density) are determined experimentally, which turn out to be consistent with existing theoretical models. (2) The optimal aperture is 5.6, because excessively large F-number causes the loss of high-frequency information and excessively small F-number leads to significant lens aberrations, both of which will reduce the measurement accuracy.

Conclusions

The optimal aperture and speckle generation parameters (speckle diameter and density) are found and proved to be uncorrelated through actual experiments in practical conditions. These results provide experimental basis for the selection of parameters in actual engineering applications.

中文翻译：

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数字图像相关中的最佳光圈和数字散斑优化

背景

数字图像相关（DIC）方法是一种无干扰，无接触的全场光学测量技术。DIC的测量精度很大程度上取决于图像采集系统和斑点图案的质量。

客观的

尽管理论上已经设计了最佳散斑图案，但是优化过程并未考虑成像系统的影响。此外，尚未获得最佳孔径。本文的目的是通过优化孔径和斑点图案来提高测量精度。

方法

本文捕获了具有不同孔径和不同斑点产生参数的斑点图像，并评估了相应的测量误差。

结果

（1）孔径的影响和散斑的优化是相互独立的。最佳斑点产生参数（斑点大小和密度）是通过实验确定的，结果与现有的理论模型一致。（2）最佳光圈为5.6，因为过大的F数会导致高频信息的丢失，而过小的F数会导致较大的透镜像差，这两者都会降低测量精度。

结论

找到最佳孔径和散斑产生参数（散斑直径和密度），并通过实际实验在实际条件下证明是不相关的。这些结果为实际工程应用中参数的选择提供了实验依据。