Underwater imaging is challenging due to the physical
properties existing in such environments. Different from
common images, underwater images suffer from poor visibility
due to the attenuation of the propagated light. The
light is attenuated exponentially with the distance and depth
mainly due to absorption and scattering effects. The absorption
substantially reduces the light energy while the scattering
causes changes in the light direction. The random
attenuation of the light is the main cause of the foggy appearance
while the the fraction of the light scattered back
from the medium along the sight considerably degrades the
scene contrast. These properties of the underwater medium
yields scenes characterized by poor contrast where distant
objects appear misty. Practically, in common sea water, the
objects at a distance of more than 10 meters are almost indistinguishable
while the colors are faded since their characteristic
wavelengths are cut according to the water depth.