Conventional auto-focus techniques in movable-lens camera systems use a measure of image sharpness to determine the
lens position that brings the scene into focus. This paper presents a novel wavelet-domain approach to determine the
position of best focus. In contrast to current techniques, the proposed algorithm estimates the level of blur in the captured
image at each lens position. Image blur is quantified by fitting a Generalized Gaussian Density (GGD) curve to a high-pass
version of the image using second-order statistics. The system then moves the lens to the position that yields the
least measure of image blur. The algorithm overcomes shortcomings of sharpness-based approaches, namely, the
application of large band-pass filters, sensitivity to image noise and need for calibration under different imaging
conditions. Since noise has no effect on the proposed blur metric, the algorithm works with a short filter and is devoid of
parameter tuning. Furthermore, the algorithm could be simplified to use a single high-pass filter to reduce complexity.
These advantages, along with the optimization presented in the paper, make the proposed algorithm very attractive for
hardware implementation on cell phones. Experiments prove that the algorithm performs well in the presence of noise as
well as resolution and data scaling.