Fig. 1. Categories of underwater polarization imaging methods

Fig. 2. Detection principle of polarization difference imaging

Fig. 3. Comparison of original intensity image and recovered image^[42]. (a) Original intensity image; (b) recovered image

Fig. 4. Comparison of polarization-sum image's PSF and polarization-difference image's PSF^[43]. (a) Polarization-sum image's PSF; (b) polarization-difference image's PSF

Fig. 5. Comparison of original intensity image and computational polarization-difference image based on the Stokes vector^[46]. (a) Intensity image; (b) polarization-difference image; (c) normalized intensity curves

Fig. 6. Recovered results and evaluation curves^[47]. (a) Curves of PCE, contrast, image sharpness, and image edge intensity; (b)--(d) recovered images of different image pairs

Fig. 7. Physical model of underwater passive polarization imaging^[40]

Fig. 8. Comparison of recovered result of traditional underwater passive polarization imaging^[40]

Fig. 9. Relationship between K(x,y) and ΔD(x,y)^[50]

Fig. 10. Comparison between original intensity image and the recovered image by Huang's method^[50]

Fig. 11. Schematic of transmittance correction^[51]

Fig. 12. Comparison between original intensity images and the recovered images by different methods^[51]

Fig. 13. Flowchart of passive underwater polarization imaging technology in neritic area^[52]

Fig. 14. Recovered images of passive underwater polarization imaging technology in neritic area^[53]. (a1) Original intensity image; (b1)--(d1) intensity distribution in the R, G, B channels of original intensity image; (a2) reconstructed image; (b2)--(d2) intensity distribution in the R, G, B channels of reconstructed image; (a3) intensity image in clear water; (b3)--(d3) intensity distribution in the R, G, B channels of intensity image in clear water; (a

Fig. 15. Recovered image of passive underwater polarization imaging technology in neritic area in real scene^[53]. (a) Original intensity image; (b) recovered image

Fig. 16. Polynomial fitting of non-uniform scene area^[54]. (a) Intensity fitting of backscattered light; (b) degree of polarization fitting of backscattered light

Fig. 17. Comparison of image restoration in non-uniform scene. (a) Recovered image by Hu's method^[54]; (b) recovered image by Schechner's method^[40]; (c) original intensity image

Fig. 18. Physical model of underwater active polarization imaging^[41]

Fig. 19. Recovered image of traditional underwater active polarization imaging^[41]. (a) Original intensity image; (b) picture of target information light; (c) picture of backscattered light

Fig. 20. Relationship between ESF, LSF, and PSF^[55]

Fig. 21. Flowchart of removing forward scattered light in active underwater imaging^[55]

Fig. 22. Restoration of badminton target^[55]. (a) Original intensity image; (b) detail enlarged view of intensity image; (c) recovered image; (d) detail enlarged view of recovered image

Fig. 23. Comparison of Fourier spectra and intensity statistics values of intensity image and recovered image^[55]. (a)(b) Original intensity image and its Fourier spectrum; (c)(d) recovered image and its Fourier spectrum; (e) intensity statistics value of the 240th row pixel of intensity image and recovered image

Fig. 24. Restoration results of different targets by multi-scale underwater polarization imaging^[56]. The left part is original intensity image and the right part is the recovered image

Fig. 25. Diagram of imaging correlation solution^[57]

Fig. 26. Recovered results in water with gradually varied turbidity^[57]. (a1)--(f1) Using blue light illumination; (a2)--(f2) using Liu's method

Fig. 27. Comparison between original intensity images and the recovered images by Feng's method^[58]. (a)(c)(e) Original intensity images; (b)(d)(f) recovered images

Fig. 28. Original intensity images and recovered images by Guan's method in turbid water with gradually varied depth^[59]

Fig. 29. Architecture of polarimetric dense network^[62]

Fig. 30. Comparison between recovered images by Polarimetric-Net and Intensity-Net^[62]. (a)--(c) Original intensity image, recovered image by Polarimetric-Net, recovered image by Intensity-Net; (d)--(f) enlarged frame of selection area