New Wavelet Methods for Flatfielding Coded Aperture Images

Abstract

We describe preliminary results from a new investigation we have undertaken for the processing of “flatfield” images used in coded aperture imaging analysis to remove spatial variations in detector background. We have explored wavelet methods for multiresolution smoothing of detector background images which preserve both high and low spatial frequency components of the detector background. Whereas original EXITE images, from the EXITE1 detector and telescope, were processed with a high-statistics average detector background image for a subtractive flatfield, any temporal variations in background shape would be better removed using the observations themselves, appropriately smoothed, to define the background shape. Wavelet smoothing, combined with a pointing program including small dither offsets (planned for EXITE2), appears to be a promising technique. Preliminary results of actual EXITE1 image analysis and simulations are presented.