Visibility for an underwater video camera is reduced by the presence of suspended particles in the water, which act in a similar manner as fog. When driving in fog, one can see the lights of other vehicles long before one can see the other vehicle in one's own headlights. This occurs as a person is distracted by the brightness of reflection from fog particles near one's own headlights. This reflected bright light prevents one from seeing dimmer targets further away.
One present way to improve the visibility of an underwater camera is to significantly separate an illumination source from the camera. However, the separation that can be achieved is limited by the width of the platform on which the illumination source and camera are located and can only provide a slight improvement.
Water currents stir up underwater particles, and as a result, their locations in a field-of-view of an underwater camera change over a period of time. U.S. Pat. No. 5,303,051 by Martin Lévesque et al describes one method of reducing the effect of underwater particles on an image by obtaining a sequence of images of an underwater scene and then comparing one image of a scene in the sequence with the others and determining the difference in each scene pixel-by-pixel. The movement of particles in the water results in different areas in each image in a sequence of images being obscured by any one particle such that by comparing pixel-by-pixel different areas in each image, a valid value for each pixel can be determined. Then a reconstructed image can be constructed from the valid values for all pixels, which significantly reduces the effect of particles in the final reconstructed image.