An algorithm for the estimation of the in-focus distance for speckle holograms

Searching and recovering the correct reconstruction distance in digital holography can be a cumbersome and subjective procedure. Here we show an algorithm for the automatically estimating the in-focus image and recovering the correct reconstruction distance for speckle holograms. We have tested the approach in determining the reconstruction distances of stretched digital holograms. Stretching a hologram with a variable elongation parameter gives us the possibility to change the in-focus distance of the reconstructed image. In this way, the proposed algorithm can be verified at different distances by dispensing the recording of different holograms. Experimental results are shown with the aim to demonstrate the usefulness of the proposed method and a comparative analysis has been performed with respect to other existing algorithms developed for digital holography.