The technique of image sharpening was first proposed by Muller and Buffington'in 1974. This work was furthered by O'Meara2 and more recently by Brigantic3. The technique is very simple and lends itself to the correction of slowly varying or static aberrations. The basic methodology is as follows;
1) Measure the system PSF or the aberrated image.
2) Characterise the image by means of an image metric. This metric will give one figure, which describes the 'quality' of the image.
3) Apply a trial correction to the wavefront corrector.
4) Reassess the image quality metric.
5) If the metric increases apply more of the same correction, if not stop and move on. Repeat until best image is achieved.
A problem lies in how do we define the 'quality' of an image through the use of a metric. There are two general requirements:
An image metric takes on the maximum value when the system is aberration free.
• The image metric needs to be calculated in a time period that is shorter than any temporal evolution of the aberration.
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Nathan P. Doble, Gordon D. Love, David F. Buscher, Richard M. Myers, Alan Purvis, "Use of image quality metrics for correction of noncommon path errors in the ELECTRA adaptive optics system," Proc. SPIE 3749, 18th Congress of the International Commission for Optics, (19 July 1999);