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.
A noise reduction method based on a shorter synthetic-wavelength in DWDH is proposed in this paper. The unwrapped phase at longer synthetic-wavelength is calculated by using the wrapped phases of two individual wavelengths. By comparing the amplified phase of longer synthetic wavelength, of which magnification is equal to that of wavelengths with the wrapped phase of a single wavelength, the difference of phase noises between the longer synthetic-wavelength phase map and the single-wavelength phase map can be calculated, and then accurate height at single-wavelength can be achieved. The proposed method for calculating phase noise is performed by comparing the phases between the single-wavelength with the shorter synthetic wavelength, and then the height at shorter synthetic-wavelength can be obtained. Compared with the existing method, the proposed method can reduce certain noise and benefit the phase reconstruction of fine structures.