Image Compression

Abstract

From year to year, the quantity of astronomical data increases at an ever growing rate. In part this is due to very large digitized sky surveys in the optical and near infrared, which in turn is due to the development of digital imaging arrays such as CCDs (charge-coupled devices). The size of digital arrays is also continually increasing, pushed by the demands of astronomical research for ever larger quantities of data in ever shorter time periods. Currently, projects such as the European DENIS and American 2MASS infrared sky surveys, or the Franco-Canadian MegaCam Survey and the American Sloan Digital Sky Survey, will each produce of the order of 10 TBytes of image data. The routine and massive digitization of photographic plates has been made possible by the advent of automatic plate scanning machines (MAMA, APM, COSMOS, SuperCOSMOS, APS, PMM, PDS) (Richter, 1998). These machines allow for digitization of the truly enormous amount of useful astronomical data represented in a photograph of the sky, and they have allowed the full potential of large area photographic sky surveys to be brought to fruition. The storage of astronomical data requires the latest innovations in archiving technology (12” or 5 1/4” WORM in the past, CD WORMS or magnetic disks with RAID technology now, DVD in the very near future). The straightforward transfer of such amounts of data over computer networks becomes cumbersome and in some cases practically impossible. Transmission of a high resolution Schmidt plate image over the Internet would take many hours.