1. A method performed by a computer for correcting misfocus in original image data, the method comprising: assigning a correction parameter value to a fractional power parameter associated with an approximation of a fractional Fourier transform operation (“FFTO”) to produce a resulting approximated FFTO; operating on the original image data with the approximated FFTO to produce transformed image data; and determining a degree of improvement in the focus of the transformed image data over that of the original image data, wherein the approximation of the fractional Fourier transform operation includes an infinitesimal generation approximation and a finite number of terms of a Hermite function expansion approximation.