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stecf.cplucy - Enhanced Two-channel Photometric Restoration

To address the problem of point-source photometry in restored images Lucy (1994) suggested a two-channel photometric restoration method in which the points are represented as $\delta-$functions in one channel and the background, constrained to be smooth by an additional entropy constraint, in the other. This method was implemented and made available as PLUCY in the stsdas.contrib package. PLUCY has the significant disadvantage that the stars were forced to be at the centres of pixels. This led either to artifacts due to inexact alignment or required the use of unreasonably large sub-sampled images. In the new CPLUCY implementation the stars can be at arbitrary x,y sub-pixel positions but the entropy constraint on the background, used by PLUCY, is retained. A superior new approach to this problem (GIRA, Pirzkal et al. 2000) is being developed and CPLUCY may be viewed as an intermediate code. Figure 1 shows an example of the application of CPLUCY to a simulated HST/NICMOS image.

 

Figure 1: An example of the application of CPLUCY. The image at the left is a simulated HST/NICMOS image with bright point-sources and structured background. The stars are at random sub-pixel positions. The centre image shows the true background intensity distribution and on the right the CPLUCY reconstructed background channel is shown.