Robert J. Hanisch & Richard L. White

This volume contains the collected papers presented at the Second Workshop on the Restoration of Images and Spectra from the Hubble Space Telescope, which was held at the Space Telescope Science Institute, Baltimore, Maryland, on 18 and 19 November 1993. The Workshop was attended by 126 registered participants. Fifty-five papers were presented in a combination of oral and poster sessions.

The Workshop was sponsored by the Image Restoration Project of the Space Telescope Science Institute. Although work on image restoration began soon after the spherical aberration problem of the HST was discovered in the summer of 1990, a dedicated effort in the area of image restoration did not get underway until the fall of 1992. Since that time, however, a small group led by Bob Hanisch and Rick White has been doing research and implementing software aimed at improving the quality of HST images. The members of this group included Ivo Busko, Jinger Mo, Nailong Wu, and Nancy Hamilton. Collaborators in the project included Don Lindler, John Krist, and Dave Baxter. Our work was also supported (through several small research contracts) by Aggelos Katsaggelos, Bobby Hunt, David Redding, and their co-workers. The Project was run out of the Advanced Systems Group of the Science Computing and Research Support Division of ST ScI.

The first workshop on HST image restoration (August 1990) presented a large variety of algorithms and approaches, but relatively little had been done to adapt these approaches to the peculiarities of HST images and spectra. The attitudes were both optimistic and, perhaps, a bit naive. HST image restoration turned out to be extremely complicated, with both spatially and temporally variable point spread functions and a variety of other instrumental effects that made high quality restorations difficult. Over the past eighteen months we have learned how to deal with many of these problems, and how to modify algorithms and generate better quality PSFs. Although HST image restoration is far from the point where an arbitrary image can be tossed into a ``black box'' deconvolution machine, good quality restoration can indeed be obtained in a large number of cases. The papers in the current volume demonstrate this quite convincingly. Perhaps the most stringent requirement on image restoration has been to retain photometric linearity. Through studies of the convergence properties of algorithms such as the Richardson-Lucy method and various Maximum Entropy approaches, we now have a good understanding of how to proceed with an image restoration so that photometric integrity is maintained. Perhaps the most profound effect of the efforts on image restoration has been to open up a new method of dealing with optical imaging data that had previously been utilized only in a segment of the astronomical community (e.g., radio astronomy).

The wonderfully successful HST Servicing Mission in December 1993 has led to HST recovering virtually all of its original design goals for optical performance. The first science images to be returned to the ground are simply awesome. The improved optical performance of the telescope allows HST to recapture the sensitivity that was irretrievably lost in the aberrated images and to tackle the observational problems that require high dynamic range. It is our expectation, however, that the algorithms and PSF modeling expertise we have developed to deal with pre-servicing mission images will continue to be useful on WFPC-II and FOC+COSTAR data. It should be possible to increase dynamic range in crowded fields, where the diffraction spikes of stars overlap to create an apparent background haze, and allow studies of the galaxies underlying quasars that are otherwise obstructed by features of the unaberrated PSF. In some cases super-resolution may be possible, extending HST's capacity for seeing detail to beyond the diffraction limit.

We would like to extend thanks to those who helped to make the Image Restoration Project and this second Workshop possible. The Project was supported by the Hubble Space Telescope Project Office at the NASA Goddard Space Flight Center. We would especially like to thank Dr. Stanley Sobieski, ST ScI's Technical Officer at the time, for his support and encouragement. Other NASA officials who were especially supportive of this work include Dr. Robert Stachnik of NASA Headquarters and Dr. Jan Hollis of NASA GSFC. Within ST ScI we thank Dr. Ron Allen for his support and guidance, and thank John Krist, the developer of the Tiny TIM PSF modeling software, which has made it possible to restore many images for which observed PSFs were not otherwise available. John's work is based on the TIM PSF modeling code developed by Chris Burrows and Hashima Hasan, who also contributed to this project through their monitoring of the time variability of the PSF. Pierre Bely also provided useful inputs in this regard, especially in the area of spacecraft pointing effects.

Robert J. Hanisch & Richard L. White
Space Telescope Science Institute
March 1994

Pages iv-v

Published version available in compressed PostScript.