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N. E. Dalrymple (AFRL), M. Bianda (IRSOL)
A person wearing dirty spectacles corrects images by observing an extended object and moving his or her head. Details that do not appear to move with the observed object must be due to optical imperfections. In the same manner, the relative pixel gains of a CCD camera observing through a movable optical system can be calculated. The result is a flat field table that may be used repeatedly to correct subsequent images. A fast flat fielding algorithm has been developed for solar observations that uses only two exposures to compute a flat field. During each exposure the source image is linearly scanned across the field of view. The two images are then mated together. The method is valid in cases where the intensity of the observed source changes slowly with respect to the camera exposure time, where the optical configuration remains constant during the scans, and where the path of motion is known or can be deduced from the images. For a camera with 2048x2048 pixels the computation requires about 30 s of processing time on a Sun 450 and yields a result that is comparable to a Kuhn-Lin flat field, which requires one hour of processing time on the same system.
The author(s) of this abstract have provided an email address for comments about the abstract: dalryn@nso.edu
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.