Underwater image enhancement by attenuation inversionwith quaternions

In this paper, an underwater image enhancement method using quaternions is presented. This work aims to improve color rendition and contrast of the objects, as if the scene has been taken out of water. This method is based on light attenuation inversion after processing a color space contraction using quaternions. Applied to the white, the attenuation gives a hue vector characterizing the water color. Using this reference axis, geometrical transformations into the color space are computed with quaternions. Pixels of water areas of processed images are moved to gray or colors with a low saturation whereas the objects remain fully colored. Thus, the contrast of the observed scene is significantly improved and the difference between the background and the rest of the image is increased, giving a first approach towards a pre-segmentation step.