TUTORIAL INTRO 2: Underwater optical 3D imaging
A pinhole camera model forms a basis of in-the-air imaging and is characterized by a single focal point. In underwater imaging camera is enclosed and observes the underwater environment through an optical interface which refracts and reflects light. Unless specifically designed, the interface causes focal spread making the simple pinhole model inapplicable. The tutorial will give an overview of geometrical image formation models which are used in underwater imaging. Then, three common tasks of camera calibration, image acquisition, and 3D reconstruction will be introduced and discussed. Next, a concept of structured light 3D imaging will be introduced. In structured light a projector, which is modeled as an inverse camera, illuminates the scene using predefined patterns with the intent to simplify 3D reconstruction. Projected patterns are always slightly blurred and can also be affected by backscatter and inter-reflections. Two common approaches which mitigate these problems, sinusoidal phase-shifted fringe patterns and Fourier profilometry will be briefly introduced and discussed.