Basic study for 2-dimensional film thickness measurement of self-indication marine paint using a visible-light camera

Coating plays a critical role in determining the service life of a ship. However, the ship coating process involves many inspection points, emphasizing the importance of enhancing inspection efficiency. Traditional inspections rely on point measurements using electromagnetic coating-thickness gauges. To improve efficiency, this study uses a noncontact method capable of assessing the two-dimensional film thickness distribution of a specific marine paint (known as self-indication paint). This innovative approach uses an inexpensive visible-light camera to capture images of the coating surface. It then analyzes the chromaticity of diffuse reflected light from this surface, employing the Kubelka–Munk theory. This analysis estimates the film thickness distribution by establishing a correlation between film thickness and chromaticity changes, ultimately determining film thickness based on chromaticity. The developed thickness estimation method agrees well with the average thickness measured via the conventional method within a certain range of paint film thickness. Furthermore, this method demonstrates the potential for measuring two-dimensional film thickness distribution, a capability unavailable with conventional methods. Therefore, this method can reduce measurement noise in assessing two-dimensional film thickness distribution while yielding results equivalent to those obtained through conventional means within a specific range.