Extended depth of field reconstruction with complex field estimation

The contradiction between high resolution and large depth of field (DOF) of microscopic imaging limits its application in imaging 3D distributed samples. Here, we propose a new technique to achieve extended depth of field reconstruction in bright-field microscopy through complex field estimation. The complex field is estimated by a phase retrieval algorithm with the four illumination modulation patterns and the corresponding captured Fourier intensities as dual constraints. Then, the digital refocusing strategy based on Fresnel propagator is integrated into reconstruction framework to achieve the reconstruction of high-resolution complex-valued information for each part of the sample, which ensures an effective extension of the DOF. The feasibility of the proposed method to maintain high resolution over extended DOF was verified in actual experiments with a tilted USAF target, biological sample and microlens array (MLA). The extended DOF reconstruction provides a robust method for imaging in both industrial inspection and biomedical research.