FOCUSING TECHNIQUES

We use the paraxial geometric optics model of image formation to deriv e a set of camera focusing techniques. These techniques do not require calibration of cameras but involve a search of the camera parameter s pace. The techniques are proved to be theoretically sound under weak a ssumptions. They include energy maximization of unfiltered, low-pass-f iltered, high-pass-filtered, and bandpass-filtered images. It is shown that in the presence of high spatial frequencies, noise, and aliasing , focusing techniques based on bandpass filters perform well. The focu sing techniques are implemented on a prototype camera system called th e Stonybrook passive autofocusing and ranging camera system (SPARCS). The architecture of SPARCS is described briefly. The performance of th e different techniques are compared experimentally. All techniques are found to perform well. The energy of low-pass-filtered image gradient , which has better overall characteristics, is recommended for practic al applications.