Underwater Microscopic Shape from Focus

Abstract

In this paper, we extend traditional Shape from focus (SFF) to the underwater scenario. Specifically, we show how 3D shape of objects immersed in water can be extracted from images captured under an optical microscope. Traditional SFF employs telecentric optics to achieve geometric registration among the frames. We extend conventional SFF to underwater objects under the assumption of negligible scattering. We establish that the property of telecentricity holds for objects immersed in water provided the numerical aperture is small. By modeling geometrical distortions due to refraction effects on the water surface, we prove that the depth map obtained in the presence of water is a scaled version of the original depth map. We also reveal that this scale factor is directly related to the refractive index of water. We validate performance with real experiments.

Layered Depth Inference from Flow in Underwater Imagery

“…The effect of refraction due to air-water interface is explicitly modeled by using the concepts of ellipse of refrax and refractive depth. Karthik et al [9] have shown that the conventional shape from focus can be extended to underwater objects. They consider an optical microscope imaging a 3D object through a still water surface.…”