Perspective and Non-perspective Camera Models in Underwater Imaging - Overview and Error Analysis

When capturing images underwater, image formation is affected in two major ways. First, the light rays traveling underwater are absorbed and scattered depending on their wavelength, creating effects on the image colors. Secondly, the glass interface between air and water refracts the ray entering the camera housing because of a different index of refraction of water, hence the ray is also affected in a geometrical way. This paper examines different camera models and their capabilities to deal with geometrical effects caused by refraction. Using imprecise camera models leads to systematic errors when computing 3D reconstructions or otherwise exploiting geometrical properties of images. In the literature, many authors have published work on underwater imaging by using the perspective pinhole camera model (single viewpoint model SVP) with a different effective focal length and distortion to compensate for the error induced by refraction at the camera housing. On the other hand, methods were proposed, where refraction is modeled explicitly or where generic, non-single-view-point camera models are used. In addition to discussing all three model categories, an accuracy analysis of using the perspective model on underwater images is given and shows that the perspective model leads to systematic errors that compromise measurement accuracy.