Quantitative phase imaging techniques (QPI) enable to observe transparent samples with high contrast and with quantitative information about their optical thickness. Among the vast family of QPI methods, two of them: (1) transport of intensity equation (TIE) and (2) digital in-line holographic microscopy (DIHM), rely on retrieving phase from several images collected with different defocus. In this work, we preliminarily investigate, mainly numerically under simulated conditions, the differences between those two methods, showing that TIE is more suitable for imaging lower-frequency objects with small defocus distance difference between collected images (around several micrometers). On the other hand, DIHM performs better for higher frequency objects and images collected with larger defocus distance difference (hundreds of micrometers). Moreover, our results show that DIHM achieves better results, when all collected images are relatively far from focal plane (in the millimeter range rather than in micrometer range), while for TIE this parameter does not have a significant influence onto the retrieved phase.
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