Study of the padding effects in numerical reconstruction of digitally recorded holograms

The reconstruction stage in the numerical reconstruction of digitally recorded holograms, imaging process named digital holography (DH), is carried out by means of computational tools. These tools are meant to reproduce the diffraction process that a known wave undergoes as it illuminates the digitally recorded hologram by using different models of light propagation. Due to the numerical nature of these methodologies some problems in their calculation, like approximations and data cuts, prevent users from obtaining more accurate results. This work shows how enlarging the size or domain of the digitally recorded hologram with digital zeros or replicas of the digital hologram, i.e. implementing padding, the visual quality of the reconstruction is improved. On using computer generated holograms of standard test images like Lena's picture and a USAF1951 resolution test target and the real hologram of a die, the effect of padding in the quality of the reconstructed holograms is quantified. The optimal values for the hologram enlargement are determined by measuring the differences between the reconstructed and the original images and by evaluating the processing time”.