Simultaneous out-of-focus blur estimation and restoration for digital auto-focusing system

Abstract

In this paper we propose a simultaneous out-of-focus blur estimation and restoration technique for a fully digital auto-focusing system. The proposed auto-focusing system can make in-focused image by using only digital image processing techniques, and it requires neither infrared light or ultrasound nor focusing lens assembly operated by a motor. As a result, it can save volume and cost of the imaging system, which contains the proposed auto-focusing system. The proposed system first divides input image into multiple sub-images or blocks, determines the set of blocks which contain linear edge, estimates the step response across the edge for each block in the selected set, computes the one-dimensional step response by averaging the step responses, estimates the two-dimensional poinst-spread-function (PSF) from the averaged step response, and finally provides in-focused image by image restoration filter based an the estimated PSF. There is a limit of the amount of out-of-focus, which can be recovered by the proposed auto-focusing system. And the proposed system is operating under assumption that an input image contains at least one piece-wise linear boundary between an object and background. In spite of the above mentioned limitations, the proposed system can make acceptible quality of focused image by using only digital signal processing.