An optimization algorithm is developed to extend the unambiguous range of DWDH, which is suitable for imaging living onion epidermal cells, and meanwhile to reduce the noise. In the experiments, the holograms with two wavelengths can be acquired in a single shot recording by using off-axis dual-wavelength digital holography, resulting to obtain their two sets of spatial spectrum via Fourier transform for these two holograms. The denoised unwrapping phase image of sample is straightforward reconstructed with the optimization algorithm, instead of increasing the noise due to longer synthetic wavelength. As a result, the unwrapped phase images of onion epidermal cells are achieved.
The optimization of image resolution for digital holographic scanning imaging of biological cells is investigated. Digital holographic scanning imaging experiments on the upper epidermal cells of onions are performed to demonstrate the validity of resolution optimization algorithm. In the experiments, the holograms of the upper epidermal cells of onion are recorded at a certain scanning rate, and then are processed by using the resolution optimization algorithm. As a result, the phase images of the onion epidermal cells with higher contrast and resolution are obtained. According to the synthetic holograms, the changes of cell nucleus and actin microfilament inside onion’s epidermal cells are displayed. In addition, the dehydration process and plasmolysis phenomenon inside onion epidermal cells are also exhibited by recording longterm scanning holograms of living epidermal cells. The experimental results demonstrate that image quality of living onion epidermal cells can be improved by optimizing the algorithms.
KEYWORDS: Holograms, Digital holography, 3D image reconstruction, Image resolution, Reconstruction algorithms, Digital imaging, Detection and tracking algorithms, Phase shifts, Spatial resolution, Signal to noise ratio
In this paper, the method of recognition and superposition of sub-pixel shifting in digital holograms is investigated. A group of non-scanning holograms is recognized and superposed by using sub-pixel shifting algorithm. Further, spatio-temporal scanning holograms with sub-pixel displacement are recognized and superposed to further improve imaging resolution by combining spatio-temporal scanning digital holography with sub-pixel shifting algorithm. The experimental results verify the feasibility of improving resolution with sub-pixel displacement.
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