Conclusions and Recommendations

Star detection is much more successful in images restored with the non-linear methods. Numerous artifacts in the linear restorations make detection of fainter stars difficult. The non-linear methods also give better astrometry results than the linear methods. The linear methods give more linear photometry results while the non-linear methods give photometry results with less RMS scatter. The hybrid approach is a good compromise giving linear flux measurements with a RMS scatter less then the linear methods.

The following approach is recommended for performing aperture photometry in restored PC images:

1. Restore the image with a non-linear restoration method. Use the result for star detection and position measurement.

2. Use the hybrid method restoration for photometry using the star list and positions from Step 1.

3. Use photometry results from a linear technique (e.g., minimum norm) to check the linearity of the results from Step 2.

We would like to acknowledge the suggestions and expert advice of the Space Telescope Science Institute's Image Restoration Project staff. This work has been supported by NASA contract NAS5-32076 funded by the Ultraviolet, Visible and Gravitational Astrophysics Research and Analysis Program.