Fig. 1. Underwater imaging model

Fig. 2. (a) Underwater calibration image and (b) minimum value filtering results

Fig. 3. Schematic diagram of uneven underwater illumination. (a) Schematic diagram of light source vertical irradiation; (b) underwater uneven illumination image

Fig. 4. Underwater calibration image and image segmentation results. (a) Underwater calibration image; segmentation results of (b) Ostu method, (c) Sauvola method and (d) the method proposed in this paper

Fig. 5. Dehazed image

Fig. 6. Technical route of image block decomposition and fusion

Fig. 7. Fusion strategies for different component

Fig. 8. (a) Grayscale distribution and theoretical distribution and (b) grayscale cumulative distribution and theoretical cumulative distribution of high-quality underwater calibration images

Fig. 9. Processing times of different numbers of image blocks

Fig. 10. Enhanced results of image blocks with different quantities. (a) 5×5; (b) 10×10; (c) 20×20; (d) 30×30

Fig. 11. Schematic diagram of underwater camera calibration

Fig. 12. Underwater calibration images and enhanced results under different turbidities. (a)~(d) turbidity are 7.6 NTU, 11.4 NTU, 15.7 NTU, 18.4NTU; (e)~(h) enhanced results by MSR; (i)~(l) enhanced results by UDCP; (m)~(p) enhanced results by ACDC; (r)~(u) enhanced results by the proposed method

Fig. 13. Target point detection results (a) before and (b) after image enhancement

Fig. 14. Number of detected target points in different postures under different turbidities; (a) 7.6NTU; (b) 11.4NTU; (c) 15.7NTU; (d) 18.4NTU