Zhang Jialin, Wu Yumin, Yang Ying, Wang Zhenguo
Opt Express. 2024 Jan 15;32(2):2619-2630. doi: 10.1364/OE.509985.
Auto-focusing is an essential task for lens-free holographic microscopy, which has developed many methods for high precision or fast refocusing. In this work, we derive the relationship among intensity derivation, the derivative of spectral distribution, as well as the distribution of the object, and propose a new auto-focusing criterion, the Robert critical function with axial difference (RCAD), to enhance the accuracy of distance estimation for lens-free imaging with the ultra-broadband light source. This method consists of three steps: image acquisition and preprocessing, axial-difference calculation, and distance estimation with sharpness analysis. The simulations and experiments demonstrate that the accuracy of this metric on auto-focusing with the ultra-broadband spectrum can effectively assist in determining the off-focus distance. The experiments are conducted in an ultra-broad-spectrum on-chip system, where the samples including the resolution target and the cross-section of the Tilia stem are employed to maximize the applicability of this method. We believe that the RCAD criterion is expected to be a useful auxiliary tool for lens-free on-chip microscopes with ultra-broadband spectrum illumination.
自动聚焦是无透镜全息显微镜的一项重要任务，为此已经开发出了许多用于高精度或快速重新聚焦的方法。在这项工作中，我们推导了强度导数、光谱分布导数以及物体分布之间的关系，并提出了一种新的自动聚焦准则——具有轴向差异的罗伯特临界函数（RCAD），以提高使用超宽带光源进行无透镜成像时距离估计的准确性。该方法包括三个步骤：图像采集与预处理、轴向差异计算以及基于清晰度分析的距离估计。仿真和实验表明，这种用于超宽带光谱自动聚焦的度量标准的准确性能够有效地辅助确定离焦距离。实验在一个超宽光谱片上系统中进行，其中使用了包括分辨率靶标和椴树茎横截面在内的样本，以最大化该方法的适用性。我们相信，RCAD准则有望成为用于超宽带光谱照明的无透镜片上显微镜的一种有用辅助工具。
