Automatic Focusing Techniques for Infrared Sensors

In this paper we study passive focusing techniques for infrared sensors. We present a survey of existing focus measures, i.e. functionals that give an estimate of the quality of focus as a function of the lens position. We synthesize the material proposed in the literature and show that all the approaches exploit the same general layout differing only for the choice of the filtering technique used to extract the image details. We present and discuss experimental results obtained on real infrared data taken in many operating conditions. The experimental analysis aims at comparing the quality of the focus measures and at evaluating their impact of the subsequent algorithm that searches the best focus position of the lens. For this purpose, we propose a comparative analysis based on three important properties of the focus measure: symmetry, smoothness and peakdnes