Processing of image intensifier data

Image intensifiers on board UVSTAR, the Ultraviolet Spectrograph Telescope for Astronomical Research, did not seem to be functioning as expected. Therefore, a simplified version of the UVSTAR electronics was used to test the image intensifiers in the laboratory. All photosensitive locations of the intensifier army were exposed at once, and then each line read each sequentially. The images which were produced had an annoying intensity gradient superimposed on them. This gradient is due to the fact that line n of the intensifier array was corrupted by thermal signal n times longer than line 1. The imagery was further degraded by the presence of so-called ''hot pixels''. These pixels correspond to locations on the intensifier's charge coupled device (CCD) array which over react to the photon flux and produce abnormally high intensity readings. This paper describes image processing techniques which removed the gradient as well as hot pixels from the intensifier imagery so that an accurate performance assessment could be made. The methods described can also be used to diagnose flaws in medical and industrial image intensifiers in general.