Fig. 1. Characteristics of spectra. (a)(c) Reference images; (b)(d) corresponding turbid underwater images; (e)(g) spectra ofreference images after Fourier transforming; (f)(h) spectra of turbid underwater images after Fourier transforming

Fig. 2. Comparisons of filtering windows. (a) Rectangular filtering window; (b) super-pixel segmentation filtering window; (c) transmission coefficient map corresponding to Fig. 2(a); (d) transmission coefficient map corresponding to Fig. 2(b)

Fig. 3. Histograms of high-contrast images without color cast. (a1)--(a4) “building2” image; (b1)--(b4) “stream” image

Fig. 4. Images after histogram adjustment. (a1)--(a4) Preliminary restored image; (b1)--(b4) output image

Fig. 5. Flow chart of algorithm

Fig. 6. Experimental results of different algorithms. (a) Original images; (b) RDCP algorithm; (c) IBLA algorithm; (d) algorithm in Ref. [9]; (e) Fusion algorithm; (f) CNN combined with HWD algorithm; (g) proposed algorithm

Fig. 7. Experimental results under different turbidities. (a) Original images; (b) RDCP algorithm; (c) IBLA algorithm; (d) algorithm in Ref. [9]; (e) Fusion algorithm; (f) CNN combined with HWD algorithm; (g) proposed algorithm

Fig. 8. Comparison of numerical results under different turbidities. (a) RMSE index; (b) SSIM index