In order to support HST operations and provide a service to the astronomical community, CASB has digitized the photographic Sky Survey plates from the Palomar and UK Schmidt telescopes. Each plate covers 6.5 x 6.5 degrees of the sky and have been digitized using a modified PDS microdensitometer with a pixel size of either 25 or 15 microns (1.7 or 1.0 arcsec respectively). These images are 14000x14000 (0.4GB) or 23040x23040 pixels (1.1GB) in size and are difficult to access quickly. To provide convenient access to these data, the images have been compressed using a technique based on the H-transform to reduce the data volume. Although the technique is lossy, it is adaptive so that it preserves the signal very well. We typically compress the data by a factor of 7, but much higher compression ratios are possible. These compressed data are then placed on CDROM for distribution and archived locally on a 1 terabyte RAID array for rapid access. Users can then easily retrieve image data for any part of the sky. The first epoch images have already been published on CDROM, and the second epoch POSS-II and SES surveys have been distributed on CDROM to a small number of institutions who are supporting the CASB effort to digitize and compress these survey plates. All of the data is available to the community through web sites at most of these centers.

Please read the fine print:

data copyrights • data use policy • data acknowledgments

We wish to thank the following institutions for supporting STScI with the publication of the DSS. 
Without their involvement, this project may not have been completed!