Digital focus detector for mobile video communicators

Theoretical analysis on digital focus detection has been conducted to uncover the underlying processes of auto focusing. According to this study, an optimal focus detector must employ an adaptive band pass filter, which takes into account both the input signal and the point spread function parameters. Focus detection efficiency of the commonly used squared gradient operator has been investigated. As shown, its performance can be essentially improved without introducing additional complexity. The modified detector is proved to be more robust, particularly operating in poor lighting conditions and has complexity acceptable for mobile imaging devices.