Innovative Image Processing Method to Improve Autofocusing Accuracy

Abstract

For automated optical inspection, autofocusing microscopes play an important role in capturing clear images of the measured object. At present, the image processing part of optics-based autofocusing microscopes often has various factors, which makes it impossible to describe the image information of the semicircular (or elliptical) spot with a simple circle-finding method. Accordingly, this study has developed a novel algorithm that can quickly calculate the ideal center of the elliptical spot and effectively compensate the linearity of the focusing characteristic curve. A prototype model was used to characterize and verify the proposed algorithm. The experimental results show that by using the proposed algorithm, the autofocusing accuracy can be effectively improved to less than 1.5 μm.

Design and Experimental Validation of an Optical Autofocusing System with Improved Accuracy

“…Impressively, this challenge is effectively addressed through the use of a sole offset lens, achieving accuracy within 3 µm without the need for supplementary compensation systems or costly optics. Furthermore, compared to previous research [19], this system introduces improvements that specifically focus on the region near the focal point, utilizing a pre-established knife-edge centroid method. In prior studies, the issue of light spot deformation had not been addressed; however, in the course of our research, we further tackled this previously unmentioned concern.…”

“…Nevertheless, it's crucial to acknowledge that the optics-based autofocus method might be susceptible to environmental factors that could potentially impact the accuracy of the focus, as indicated by some studies [15]. Currently, numerous researchers are dedicated to enhancing the accuracy of optical autofocus, whether through improving hardware components [16,17] or employing advanced image processing techniques [1,[18][19][20][21][22]. Despite the beneficial aspects of various methods, it has been observed that, regardless of the means used to improve autofocus accuracy, the light spot detected by the light sensor may undergo significant distortion when the test object is near the focus point.…”