<title>Ambiguities in shape from underwater image shading</title>

Abstract

Shape from shading has been extensively studied in the field of computer vision. Most research in this area assumes a non-attenuating medium, such as air. Generally speaking, the developed methods cannot be directly used for applications in undersea environments where the absorption and scattering of the medium may not be negligible. In this paper, we present an image irradiance model for a Lambertian surface illuminated by a point source in an attenuating medium such as seawater. This model has been used to recover the orientation of uniform planar patches. Our current experimental data show that the developed model also provides a quite accurate approximation of the image brightness of curved surfaces. In this paper, we discuss several ambiguities in the solutions based on this model and compare them with solutions in land-based systems. Our discussion mainly involves case studies of ruled surface which can be reduced to 1-D cases in the computation. The results presented in this paper are useful for image understanding and/or object recognition in underwater applications.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.