1 March 2013 Autofocusing in digital holography
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Digital holography allows the acquisition of 3D profiles of objects. Digitally captured holograms are reconstructed at the respective distances of the objects to reveal the phase and the intensity profiles. However, computing an object’s 3D profile with only a single reconstruction requires prior knowledge of the distance of the object from the camera. Otherwise, by performing several reconstructions at different distances and by evaluating each image with sharpness estimation, one can determine the in-focus distance of the object. Moreover, it is not practical to perform several reconstructions in real-time systems since reconstruction is the most computationally heavy part in digital holographic imaging. In this paper, we compare common sharpness functions applied to digitally recorded holograms for autofocus algorithms found in the literature. In addition, we show that automatic focus distance search can be done in real-time with scaled-down holograms obtained from the original hologram. This new method improves the speed of autofocus algorithms on the order of square of the scaling ratio. We show that numerical simulations and experimental results are in good agreement.
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Hazar A. İlhan, Hazar A. İlhan, Mert Doğar, Mert Doğar, Meric Özcan, Meric Özcan, "Autofocusing in digital holography", Proc. SPIE 8644, Practical Holography XXVII: Materials and Applications, 86440C (1 March 2013); doi: 10.1117/12.2002038; https://doi.org/10.1117/12.2002038

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