1 November 1993 Focusing techniques
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Optical Engineering, 32(11), (1993). doi:10.1117/12.147706
We use the paraxial geometric optics model of image formation to derive a set of camera focusing techniques. These techniques do not require calibration of cameras but involve a search of the camera parameter space. The techniques are proved to be theoretically sound under weak assumptions. They include energy maximization of unfiltered, low-pass-filtered, 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 focusing techniques are implemented on a prototype camera system called the Stonybrook passive autofocusing and ranging camera system (SPARCS). The architecture of SPARCS is described briefly. The performance of the 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 practical applications.
Murali Subbarao, Tae-Sun Choi, Arman Nikzad, "Focusing techniques," Optical Engineering 32(11), (1 November 1993). http://dx.doi.org/10.1117/12.147706


Image filtering

Optical transfer functions

Linear filtering

Point spread functions

Imaging systems

Bandpass filters

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