Twin-image suppression in digital in-line holography based on wave-front filtering

Digital holography is an imaging process able to recreate three-dimensional representations of objects from recording pattern interference among distinct waves. The in-line configuration setup is a variant considered the simplest physical implementation, providing a feasible manner for acquisition and the same time higher resolution for free-living microscopy imaging using a single illumination system. However, the well-known twin-image problem is bounded to the technique, since there is no separation among reference and objects beams in this configuration. As a result, computational numerical diffraction routines present the twin-image effect intrinsically, imposing several difficulties in terms of post-processing requirements. In this context, this paper aims to present a numerical approach able to provide consistent suppression of twin-image problem for in-line holography, during the numerical diffraction procedure for phase retrieval, combining image subtraction and edge detection techniques. The proposed solution was implemented in Python language, and metrics defined to assess it were both qualitative and quantitative, based on edge detection and some image comparison metrics. The obtained results of the proposed approach present a significant reduction in the twin-image artifacts in the reconstructions of both experimental and simulated holograms, considering a spherical reference wave, regardless of the shapes and sizes of objects.