Deskewing of underwater images

Publication

Karthik Seemakurthy and A.N. Rajagopalan, ``Deskewing of underwater images'', IEEE Transactions on Image Processing, Vol. 24, Iss. 3, pp.1046--1059, March 2015.

Abstract

We address the problem of restoring a static planar scene degraded by skewing effect when imaged through a dynamic water surface. Specifically, we investigate geometric distortions due to unidirectional cyclic waves and circular ripples, phenomena that are most prevalent in fluid flow. Although the camera and scene are stationary, light rays emanating from a scene undergo refraction at the fluid-air interface. This refraction effect is time-varying for dynamic fluids and results in non-rigid distortions (skew) in the captured image. These distortions can be associated with motion blur depending on the exposure time of the camera. In the first part of the
paper, we establish the condition under which the blur induced due to unidirectional cyclic waves can be treated as space-invariant. We proceed to derive a mathematical model for blur formation and propose a restoration scheme by using a single degraded observation. In the second part, we reveal how the blur induced by circular ripples (though space-variant) can be modeled as uniform in the polar domain and develop a method for deskewing. The proposed methods are tested on synthetic as well as real examples.