Fig. 1. Structured light measurement system

Fig. 2. Scanning imaging idea based on structured light illumination mode

Fig. 3. Determination of window mask. (a) Cross-sectional intensity distribution of the projected light strip and the preset threshold of the window mask; (b) gray value distribution along the x direction (dotted line) after smoothing and filtering; (c) single-frame image without backscattered light

Fig. 4. Flow chart of obtaining illumination-independent image and center extraction

Fig. 5. Experimental setup

Fig. 6. Imaging in turbid water. (a) Pan-lighting image; (b) structured-light scanned image

Fig. 7. Backscattering removal using “virtual aperture”. (a) Integral composited image; (b) backscattering removal image; (c) restored image

Fig. 8. Restored images and average gradient images before and after removing backscattering. (a) Restored image before backscattering removal; (b) restored image after backscattering removal; (c) average gradient image of Fig. 8 (a); (d) average gradient image of Fig. 8 (b)

Fig. 9. Experimental results of center extraction. (a) Single-frame image after backscatterring removal by “virtual aperture” method; (b) center extraction result using the “direction template” method; (c) light stripe image after texture removal by applying illumination-independent image; (d) center extraction result using the “direction template” method after texture removal; (e) position of the center line of Fig. 9 (d) in the light strip

Fig. 10. Sub channel processing results. (a) Pan-illumination image; (b) integral composited image; (c) restored image

Table 1. Evaluation of color images