Implementation of a modified Richardson-Lucy method for image restoration on a massively parallel computer to compensate for space-variant point spread of a charge-coupled-device camera

Abstract

Several imaging devices are characterized by a space-variant point-spread function (PSF), such as the wide-field/planetary camera of the Hubble Space Telescope (HST). Several techniques for image recovery that use data from such imagers approximate the space-variant PSF by a space-invariant PSF. A modified Richardson-Lucy method is implemented that accommodates the space-variant PSF of the HST as well as corrections for background counts, nonuniform flat field, and readout noise. The implementation runs on the DEC mppl2000 Sx/Model 200 massively parallel computer. Restorations of simulated HST images are obtained with a space-variant PSF and, for comparison, with a space-invariant approximation. Results of these processing methods are compared, and it is found that a residual artifact appears in restorations when a space-invariant PSF is used owing to the mismatch of the PSF kernel used in the restoration and the space-variant one underlying the image acquired with the telescope. This residual artifact is effectively eliminated when the processing is based on the space-variant PSF.