Universal illumination angle calibration for Fourier ptychographic microscopy via a parallel feature shifting strategy

Fourier ptychographic microscopy (FPM) can achieve high-resolution and large field-of-view complex field imaging via phase retrieval and a synthetic aperture using a series of low-resolution intensity images captured under angularly varying illumination. While powerful, it exhibits sensitivity to illumination angle deviation, which can cause significant artifacts during the reconstruction process. To address this limitation, we propose a Parallel Feature Shifting (PFS) strategy, a robust and universal illumination angle calibration method utilizing the lateral shift of features on a dual-sided calibration mask under oblique illumination. The PFS strategy can accurately retrieve the illumination vectors by calculating the relative shift between the ring and disk array patterns on the opposing surfaces of the calibration mask. By combining a rigorous physical model with system-agnostic operation principles, the PFS strategy demonstrates strong tolerance to misalignment and provides a universal framework for angle calibration in illumination-angle-encoded computational microscopy systems.