Modeling phase shift data of phase-detection autofocus by skew-normal distribution

摘要

Recent mobile imaging seeks to expedite the autofocus process by embedding a phase detector in the image sensor to provide information for controlling both the magnitude and direction of lens movement. Compared to conventional contrast-detection autofocus, phase-detection autofocus (PDAF) is able to quickly bring the lens toward the in-focus position. However, the presence of sensor noise, the lack of image contrast, and the spatial offset between the left and right phase detectors can easily affect the performance of phase detection. We present a statistical approach to address this issue by characterizing the distribution of phase shift for a given distance of the lens to the in-focus position. We model the phase shift as a skew-normal distribution and verify it empirically. The results show that the skew-normal distribution is indeed a proper model for the phase shift data. We also propose a method based on Bayes' theorem to determine the lens movement. Experimental results show that the proposed method is able to improve the reliability of PDAF. (C) 2019 SPIE and IS&T