Polarization Imaging Method for Underwater Low-Visibility Metal Target Using Focus Dividing Plane

Abstract

Aiming at the problems of brightness attenuation and contrast reduction in the target image caused by underwater low-visibility environments, a metal target detection method based on split-focus plane polarization imaging is proposed. Firstly, a hybrid enhancement method is proposed to clarify the degraded polarization image. In this study, the GrayWorld method is improved to compensate the attenuation difference of the total light intensity of the polarization image. Variational contrast and saturation enhancement algorithms are used to reduce the underwater scattering effect; secondly, a split-focus plane polarization imaging system is built to complete the control of camera parameters, polarization image acquisition and information processing. Under different underwater low-visibility conditions, polarization imaging of targets with different materials can be realized; finally, an image quality evaluation system is constructed to compare the light intensity and degree of polarization images that are collected by the focal plane polarization imaging system. The polarization characteristics of metal and nonmetal target plates are analyzed. The results show that under the condition of low visibility, the obtained polarization image contrast of the metal target is relatively high, and its EME, information entropy and average gradient are increased by 183.82%, 53.46% and 586.22% on average relative to the image of light intensity. In an underwater low-visibility scene, the method of focal plane polarization imaging proposed in this paper can reduce the difficulty of metal target detection.

Underwater polarization image restoration based on a partition method

“…Thus, visible light imaging has become an area of active research and application in deep-sea exploration 5 – 7 However, compared to air, visible light transmission in water experiences significant attenuation, while impurity particles in natural water degrade underwater images. The reason for this degradation is due to the reflection and refraction of light reflected by the target on the surface and inside the impurity particles, resulting in multiple reflections and refractions that ultimately mix with the reflected light from the target, thereby deteriorating the image quality 8 , 9 .…”