Off-axis digital holography (DH), which is based on a Mach-Zehnder interferometer asshown in Fig. 1, is used to acquire digital holograms for 3D image reconstruction. In the offaxis configuration, the coherent laser source is divided into an object (O) and a reference waves (R) using the beam splitter. The object wave illuminates the sample such as red blood cells and creates object wave front. The microscope objective (MO) collects and magnifies the object wave front. A detector such as a CCD camera records the hologram generated by the interference of the object wave and the reference wave, which is incident at a small angle (θ) with respect to the object wave, as shown in the inset of Fig. 1. The recorded holograms are sent to the PC for filtering, encrypting and multiplexing, and reconstruction of the phase contrast image.When the 3D image is reconstructed numerically on computer from the recorded digitalhologram, the reconstructed image includes zero-order noise of diffraction (the first two terms in Eq. (1)) and the virtual image (or twin image) and the real image, which correspond to the third and fourth terms in Eq. (1), respectively [19,34].We need to suppress the undesired data, i.e. zero-order noise and virtual image, byapplying a digitally defined filter mask to a Fourier transform of the hologram in the spatial spectrum domain. This is shown in Fig. 2(c) and results in the filtered hologram, which is shown in Fig. 2(d) and represented by