I. Introduction
The limited depth of field of optical systems is a common problem in image acquisition since it leads to the defocusing of those parts of the depicted scene that are not comprised within the in-focus limits, hence affecting the quality and amount of information that can be retrieved from the captured images. In particular, when images are captured with a low depth-of-field system, the objects at different depths from the camera may appear out of focus if they are away from the focus plane.