Auto-focusing method for wide-spectral-illumination lens-free imaging

Auto-focusing plays a crucial role in lens-free holographic microscopy. In this research, we propose a new axialdifference- based Robert method aimed at improving the accuracy of distance estimation under wide-spectral illumination. By establishing connections between intensity derivation, spectral distribution changes, and object distribution, we develop a robust method. The procedure involves image acquisition, preprocessing, axial difference computation, and sharpness-based distance determination. Both simulations and experiments verify the method’s ability to enhance auto-focusing accuracy in wide-spectral illumination scenarios. To demonstrate its broad applicability, experiments are carried out using ultra-wide-spectral illumination on various samples, including a resolution target and a Tilia stem cross-section.