Fig. 1. Schematic diagram of the underwater laser imaging experiment

Fig. 2. Experimental setup for red, green and blue lasers

Fig. 3. Output spectrum of semiconductor white laser

Fig. 4. Output spectrum of the semiconductor red laser

Fig. 5. Output spectrum of the semiconductor green laser

Fig. 6. Output spectrum of the semiconductor blue laser

Fig. 7. Underwater lighting test with different light sources

Fig. 8. The lighting effect of different light sources illuminating green leaves, safflower and oranges in clear water at a distance of 5 cm from the water surface

Fig. 9. The lighting effect of different light sources illuminating green leaves, safflower and orange targets in clear water at a distance of 19 cm from the water surface

Fig. 10. The lighting effects of different light sources illuminating green leaves, safflower, and oranges in seawater at a distance of 5 cm from the water surface

Fig. 11. The lighting effects of different light sources illuminating green leaves, safflower, and oranges in seawater at a distance of 19 cm from the water surface

Fig. 12. Images of different size templates with the underwater imaging distance of 19 cm processed by median filter method. (a) Original image; (b) gray image; template processing results with (c) 3×3 window size; (d) 5×5 window size; (e) 7×7 window size; (f) 9×9 window size

Fig. 13. Image processing results of the histogram equalization algorithm with an underwater imaging distance of 19 cm

Fig. 14. Original image (left) and processing results (right) of piecewise linear grayscale transformation of underwater imaging at a distance of 19 cm

Fig. 15. Imaging results with different light sources when the underwater imaging distance is 15 cm in clear water and seawater

Fig. 16. Imaging with different light sources near the water surface in clear water and seawater

Fig. 17. Image processing results obtained with the light source LED1 in seawater imaging on the water surface

Fig. 18. Image processing results obtained with the light source LED2 in seawater imaging on the water surface

Fig. 19. Image processing results obtained with the light source white laser in seawater imaging on the water surface

Fig. 20. Image processing and evaluation method

Fig. 21. Image processing results of object A taken near the water surface under different white light sources in seawater

Fig. 22. Image processing results of object B taken near the water surface under different white light sources in seawater