Fig. 1. Underwater in situ holographic imaging system. (a) System optical path structure; (b) schematic of optical path; (c) physical drawing

Fig. 2. Partial holograms captured by the system

Fig. 3. Reconstruction results of hologram. (a) Pre-reconstruction resolution plate image; (b) post-reconstruction resolution plate image; (c) pre-reconstruction biological specimen image; (d) post-reconstruction biological specimen image; (e) pre-reconstruction underwater microbial 1 image; (f) post-reconstruction underwater microbial 1 image; (g) pre-reconstruction underwater microbial 2 image; (h) post-reconstruction underwater microbial 2 image

Fig. 4. Comparison of interference fringe filtering spectra. (a) Spatial domain image before filtering; (b) frequency domain image before filtering; (c) spatial domain image after filtering by traditional method; (d) frequency domain image after filtering by traditional method; (e) spatial domain image after filtering by improved method; (f) frequency domain image after filtering by improved method

Fig. 5. Interference stripe filtering effect. (a) Resolution plate image before filtering; (b) resolution plate image after filtering; (c) biological specimen image before filtering; (d) post-filtered biological specimen image; (e) pre-filtered biological specimen image; (f) post-filtered biological specimen image

Fig. 6. Underwater microbial contour segmentation network architecture

Fig. 7. Structure diagram of background scattering estimation module

Fig. 8. Structure diagram of direct transmission estimation module

Fig. 9. Network structure of contour segmentation task

Fig. 10. Local refinement algorithm

Fig. 11. Image fusion effect. (a) (b) (c) Images without water; (d) (e) (f) images with water; (g) (h) (i) annotation

Fig. 12. Comparison of contour representation capabilities

Fig. 13. Experimental errors. (a) Regularly shaped microorganisms; (b) irregularly shaped microorganisms

Fig. 14. Comparison of spatial continuity

Fig. 15. Errors of spatial continuity

Fig. 16. Segmentation results of different algorithms