We have evaluated various image restoration techniques (both linear and non-linear) applied to a simulated crowded star field observed with the HST Planetary Camera (PC). Evaluation criteria included star detection, astrometry, and photometry. Numerous restoration artifacts made star detection difficult for the linear restorations. The non-linear methods give much better star detection and slightly better astrometry results. Aperture photometry measurements in images restored with the non-linear restoration methods show significant non-linearities. The flux of fainter stars are systematically underestimated. This problem is not seen in the images restored with the linear methods. However, we see significantly increased RMS scatter in the photometry results for images restored with a linear method. We found that a hybrid approach which combines the result of a non-linear method with a linear method will give linear photometry results with lower RMS scatter.
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