Enhanced image reconstruction of Fourier ptychographic microscopy with double-height illumination

Fourier ptychographic microscopy (FPM) is a recently developed computational microscopy approach that can produce both wide field-of-view and high-resolution intensity and phase image of the sample. Traditionally, a periodic LED array is used as the illumination source. The frequency spectrum is a grid structure that is sparse in the low-middle frequency region and dense in the high-frequency region. However, for most biological samples, the useful information is mostly concentrated in the low-middle frequency region. So the traditional sampling method may lead to distortion in the reconstructed images because of insufficient sampling. Therefore, we propose a convenient and feasible method to continuously improve the sampling conditions without increasing the LED units and changing the pitch, termed double-height illumination FPM. The LED array is moved from one plane to another to achieve the sample illuminations at two different heights and the low-resolution intensity images are totally utilized to reconstruct the high-resolution complex amplitude image. Both simulation results and experimental results illustrate that the proposed method not only improves the reconstruction accuracy and efficiency, but also has strong robustness under noisy conditions. Furthermore, the rule of choosing the two illumination heights is discussed, and the physical insight of the proposed method is analyzed from the view of the data redundancy. In addition, a wave vector correction method is employed to reduce the artifacts of the reconstructed image at the edge of the large full field of view.