Fig. 1. Transmission off-axis digital holographic microscopic focusing imaging system

Fig. 2. Sample images. (a) Simulated image sequence; (b) image sequence obtained by microscopic imaging; (c) image sequence obtained by digital holographic microscopic imaging

Fig. 3. Digital holographic focusing imaging algorithm based on Butterworth feature function

Fig. 4. Filtering results of BLPF function under different orders. (a) n=1; (b) n=2; (c) n=3; (d) n=4; (e) n=5

Fig. 5. PSNR variation curve of images under different orders

Fig. 6. Comparison of hologram images before and after fringe suppression. (a) Before fringe suppression; (b) after fringe suppression

Fig. 7. Comparison between calculation results of two groups of data before and after being processed by proposed algorithm, calculated using five gradient operators. (a) Focusing evaluation results; (b) partially enlarged for peak positions of curves; (c) partially enlarged for flat areas of curves; (d) focusing result of phase resolution plate

Fig. 8. Phase reconstruction results of focusing position hologram. (a) Section line results; (b) phase reconstruction results of resolution plate; (c) three-dimensional reconstruction results of resolution plate