A self-adaptive and nonmechanical motion autofocusing system for optical microscopes

Abstract

For the design of a passive autofocusing (AF) system for optical microscopes, many time-consuming and tedious experiments have been performed to determine and design a better focus criterion function, owing to the sample-dependence of this function. To accelerate the development of the AF systems in optical microscopes and to increase AF speed as well as maintain the AF accuracy, this study proposes a self-adaptive and nonmechanical motion AF system. The presented AF system does not require the selection and design of a focus criterion function when it is developed. Instead, the system can automatically determine a better focus criterion function for an observed sample by analyzing the texture features of the sample and subsequently perform an AF procedure to bring the sample into focus in the objective of an optical microscope. In addition, to increase the AF speed, the Z axis scanning of the mechanical motion of the sample or the objective is replaced by focusing scanning performed by a liquid lens, which is driven by an electrical current and does not involve mechanical motion. Experiments show that the reproducibility of the results obtained with the proposed self-adaptive and nonmechanical motion AF system is better than that provided by that of traditional AF systems, and that the AF speed is 10 times faster than that of traditional AF systems. Also, the self-adaptive function increased the speed of AF process by an average of 10.5% than Laplacian and Tenegrad functions.

Focus measure method based on the modulus of the gradient of the color planes for digital microscopy

“…As stated by Qu et al, 1 different focus criterion functions perform quite differently even for the same sample. The majority of these methods have been addressed to study AF in the context of monochromatic frames.…”

A Method for Medical Microscopic Images’ Sharpness Evaluation Based on NSST and Variance by Combining Time and Frequency Domains

“…In view of the defects of the active focus mode, the passive focus method based on image processing has been widely implemented, with the purpose of obtaining a real-time image dataset of the microscope, analyzing the current image focus state, and controlling the stepper motor to modify the step size according to specific search strategies and to obtain as sharp of an image as possible. As indicated by Qu et al [ 3 ], even for the same sample, the performance of different focus criterion functions will be quite different. In this process, therefore, the key question is how to choose a suitable evaluation function to judge the sharpness of images.…”

Nonmechanical and multiview 3D measurement microscope for workpiece with large slope and complex geometry

“…Qu et al . () realized a self‐adaptive and nonmechanical‐motion autofocusing system using a liquid lens. Qu & Yang () extended the depth of field by using a varifocal liquid lens.…”

“…Jabbour et al (2014) used a liquid lens in confocal microscopy for Z-axial scanning. Qu et al (2016) realized a self-adaptive and nonmechanicalmotion autofocusing system using a liquid lens. Qu & Yang (2015) extended the depth of field by using a varifocal liquid lens.…”