A Closed-Form Focus Profile Model for Conventional Digital Cameras

According to the thin lens model, the classic depth of field (DOF) is defined as the distance range at which objects in front of a camera are in focus. However, the thin lens poses important practical limitations for modeling the camera focus due to its dependence on internal parameters, such as the focal length, numerical aperture and effective pixel size. In this paper, a new model for describing the focus of conventional digital cameras is proposed. The focus is modeled as the energy of the point-spread-function of the imaging system and describes the joint effect of defocus, diffraction and digitization. Experiments conducted on different acquisition devices show that the proposed model conforms accurately to the behavior of real systems and outperforms the most similar alternatives in the state-of-the-art. In addition, in contrast to the classic DOF model, the proposed approach can be used to predict the changes in the focus of conventional digital cameras when changing focus, zoom, and aperture by means of a simple calibration process.