This paper proposes an approach based on two orthogonal views and two wavelengths for recording off-axis two-color holograms. The approach permits to discriminate particles aligned along the sight-view axis. The digital processing to get images from the particles is based on convolution so as to obtain images with no wavelength dependence. In order to get the images of particles in the 3D volume, a calibration process is proposed and is based on the modulation theorem to perfectly superimpose the two views in a common XYZ axis. The experimental set-up is applied to two-color hologram recording of moving non-calibrated opaque particles with average diameter at about 150μm. After processing the two-color holograms with image reconstruction and view calibration, the location of particles in the 3D volume can be obtained. Particularly, ambiguity about close particles, generating hidden particles in a single-view scheme, can be removed to determine the exact number of particles in the region of interest.
This paper proposes a quality assessment of focusing criteria for imaging in digital off-axis holography. In literature,
several refocus criteria have been proposed in the past to get the best refocus distance in digital holography. As a general
rule, the best focusing plane is determined by the reconstruction distance for which the criterion function presents a
maximum or a minimum. To evaluate the robustness of these criteria, a set of thirteen criteria is compared with
application on both amplitude and phase images from off-axis holographic data. Experimental results lead to define
general rule and to exhibit the most robust criteria for accurate and rapid refocusing in digital holography.
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