This paper investigates the application of Fresnel based numerical algorithms for the reconstruction of
Gabor in-line holograms. We focus on the two most widely used Fresnel approximation algorithms,
the direct method and the angular spectrum method. Both algorithms involve calculating a Fresnel integral,
but they accomplish it in fundamentally different ways. The algorithms perform differently for different
physical parameters such as distance, CCD pixel size, and so on. We investigate the constraints for
the algorithms when applied to in-line Gabor digital holographic microscopy. We show why the algorithms
fail in some instances and how to alter them in order to obtain useful images of the microscopic
specimen. We verify the altered algorithms using an optically captured digital hologram