Fig. 1. Principle of range-gated imaging^［58］

Fig. 2. Underwater range gated imaging devices. (a)‒(c) LUCIE 1-3 series products developed by Canada^[60-61]; (d) Aqua Lynx system developed by Sweden^[62] ; (e) system developed by Beijing University of Science and Technology^[64]; (f) system developed by the United States^[63]; (g) “Phoenix Eyes” system developed by the Institute of Semiconductors, Chinese Academy of Sciences^[65]

Fig. 3. Method based on statistical modeling of echoes^[66]. (a) Diagram of the experimental setup; (b) experimental results, with the degree of scattering gradually increasing from left to right for both sets of data

Fig. 4. Application of ghost imaging in scattering environments. (a)(b) Experimental setup and results in the laboratory by Gong et al.^[73]; (c)(d) experimental setup and results outdoors by Chen et al.^[74]; (e)(f) experimental setup and results underwater by Li et al.^[75]

Fig. 5. Principles of optical coherence tomography and its applications. (a) Schematic diagram of time-domain OCT; (b) schematic diagram of spectral-domain OCT; (c) schematic diagram of swept source OCT; (d) OCT prototype^[98] ; (e1)(e2) retina of a normal human eye and its in vivo images by OCT^[99]; (f1)(f2) photograph and schematic of an OCT endoscope for intraluminal imaging^[100-101]; (g1)(g2) OCT images of normal colon and malignant adenoma^[102]; (g3)(g4) tissue sections images corresponding to Figs. 5 (g1) and (g2)^[102]

Fig. 6. Principle of wavefront shaping and experimental results^[37,114]. (a) Experimental setup; (b) before wavefront shaping; (c) after wavefront shaping; (d) speckle patten before shaping; (e) refocused image after shaping; (f) conventional optical imaging system; (g) super-resolution imaging system based on wavefront shaping; (h) focal point of the conventional imaging; (i) speckle patten formed by a conventional imaging system through the scattering medium; (j) super-resolution refocused focal point by wavefront shaping; (k) optimized wavefront phase

Fig. 7. Principle and experimental results of optical phase conjugation^[128] . (a) Conventional imaging system without scattering medium; (b) conventional imaging system with scattering medium; (c) optical phase conjugation imaging through scattering medium

Fig. 8. Principle and experimental results of transmission matrix measurements^[38,134]. (a) Diagram of the experimental setup; (b1) speckle pattern through the scattering medium; (b2) single-point refocusing result; (b3) norm of the focusing operator; (b4) 3-point refocusing result; (c) reconstructed images; (d) correlation coefficient between reconstruction and object as a function of the asymmetric ratio

Fig. 9. Scattering imaging based on optical memory effect. (a) Principle of optical memory effect^[42] ; (b) diagram of the experimental setup^[12] ; (c) speckle pattern; (d) reconstructed object image

Fig. 10. Principle of NLOS imaging and experimental results. (a) Diagram of the TOF based NLOS imaging experimental setup^[151]; (b) measured echoes; (c) recovered results; (d) diagram of the TOF based NLOS imaging experimental setup in the outfield^[159]; (e) hidden human body model; (f) three-dimensional results of recovered model; (g) experimental setup of broad spectrum light NLOS imaging^[140]; (h1) camera detected speckle pattern; (h2) recovered object image; (h3) original object; (i) white light NLOS imaging experimental setup^[162] ; (j1) speckle pattern; (j2) optimized autocorrelation result; (j3) recovery result

Fig. 11. Histogram equalization. （a） Clear image， （b） fog image； （c） the histogram equalization result； （d）‒（f） grayscale histograms of Figs. 11 （a）‒（c）

Fig. 12. Schematic diagram of Retinex^[173]

Fig. 13. Atmospheric scattering model^［48］

Fig. 14. Dark channel prior dehazing process and results^[53]. (a) Data process; (b) raw images; (c) recovery results; (d) estimated depth maps

Fig. 15. Method for maximizing image contrast^[55]. (a) Clear image; (b) haze image; (c) distribution of edges of the region in the red rectangle; (d) input image; (e) recovery image; (f) estimated airlight

Fig. 16. Principles and results of polarization defogging^[54]. (a) Relationship between captured light intensity and polarized angle; (b) brightest/worst polarized image; (c) darkest/best polarized image; (d) recovery results; (e) detail comparison of the best-polarized and recovery images

Fig. 17. Principle and results of angle-selection scattering imaging^[210]. (a) Imaging schematic; (b) experimental setup; (c) single-frame SIR enhancement results, where I) is the raw image acquired by the imaging system without angle-selection, II) and III) with angle-selection, and IV), V), and VI) are the corresponding histogram equalization results, respectively; (d) schematic diagram of time-domain minimization filtering; (e) multi-frame recovery results for different visibility, where I) is the raw images, II), III) and IV) are the recovery results of single-frame, multi-frame superposition, and time-domain minimization filtering, respectively

Fig. 18. Deep learning based scattering imaging in active mode. (a) Experimental setup of static scattering medium^[231] ; (b) recovery results of static scattering medium; (c) experimental setup of dynamic scattering medium^[232] ; (d) recovery results of dynamic scattering medium

Fig. 19. Passive scattering imaging based on e-ink displays^[259]. (a) Experimental Setup; (b) data sample, consisting of e-ink displays and real objects, used to train and test the network; (c) recovery results and comparison with conventional algorithms