Digital holographic autofocusing algorithm based on fractional Fourier transform gradient

In this paper, a novel digital holographic autofocusing method based on Fractional Fourier Transform Gradient (FrFTG) is proposed to address the autofocusing issue in digital holography systems. The method first applies the fractional-order Fourier transform to the captured hologram, then utilizes a gradient operator to extract the edges of the image in the fractional-order domain. This results in a fusion of the spatial and frequency domain gradient components. Such a combination makes FrFTG more suitable for scenarios where image quality deteriorates due to defocusing. Additionally, the fractional-order Fourier transform provides a flexible and tunable fractional-order dimension, which can be adapted to various sample types and focusing conditions. Simulation and experimental results validate the effectiveness and practical value of the proposed method in off-axis digital holographic autofocusing tasks.