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The well-known effects of defocusing in analog linear imaging systems allow to define an infinite class of focus measures in the frequency domain. All measures are calculated as weighted squared moduli of the spectrum. In digital linear systems a subset of them yields useful focus measures. They are applicable to every object, define the physical focus, and can be translated back to the space domain, where the computation is less expensive. The sum of the squares of a modified second derivative of the image pixel values seems to be the best focus meas-ure for practical purposes.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
