Color correction and dynamic range expansion of underwater images based on light field technology

Compared with images taken in the air, underwater images are susceptible due to the adverse effects of complex water conditions, such as absorption, attenuation, scattering, various noises, and uneven lighting, etc. These effects severely reduce the quality of underwater imaging and give rise to many problems among which is image color distortion. To fully acknowledge the underwater scenes, it is important to acquire the images with accurate colors, especially for marine rescue, underwater target recognition, and marine ecological research. To address this problem, this paper proposes an underwater imaging technology based on a light field camera array. The application of this technology can not only perform accurate color correction processing on the captured images but also expand the dynamic range of underwater images, thereby obtain enhanced high-quality, true-color underwater images. The experimental system in this paper contains a 3*3 camera array that simultaneously captures images of underwater targets with different exposure times. As the light attenuation coefficient of different wavelengths in water varies with the wavelength, during the color restoration process, we measure the relative value of the underwater spectral power distribution concerning the air, calculate the tristimulus value change according to the colorimetric principle, and convert the tristimulus value change in the CIEXYZ color space to the CIE La*b* color space. The color on the underwater images obtained by the camera array is then compensated. Then, in the image fusion process, images with different exposure are used to recover the response function of the imaging process, and multiple images are fused into a single, high-dynamic-range radiance map using high quality tone mapping technique in the radiance value dynamic display high-contrast images on devices with limited range. Experimental results show that our light-field imaging color correction and dynamic range expansion processing methods have obvious advantages over single cameras in underwater color correction and underwater moving target imaging detection, which provide advanced technology and equipment for underwater in-situ applications.