Attenuating natural flicker patterns

Waves on the water surface create spatio-temporal illumination patterns underwater. Concave regions on the surface diverge light rays refracting into the water, while convex regions create convergence of rays (caustics). Therefore, the natural illumination of underwater objects is spatially varying. Moreover, in shallow water this nonuniform intensity distribution varies significantly in time, as the water surface changes with the wave motion. In this paper we present a method that attenuates these illumination patterns, and results in an image which appears as if taken under much more stable and uniform illumination. The method is based on just a few consecutive frames taken of the scene. These frames are analyzed by a non-linear algorithm which preserves consistent image components while filtering out fluctuations. The use of the nonlinear algorithm alleviates the need for long acquisition periods and is therefore fast. We demonstrate its effectiveness and efficiency in underwater experiments