Image processing of historical astronomical plates

Many fields of X-ray astrophysics require multifrequency data including optical. Long-term data, such as provided by data archives, have special value. Historical astronomical plates were main source of data for more than century, not only for photometry, but also for spectroscopy. There are still millions of plates worldwide which have never been processed by modern computers. There are some standard ways how to process images applicable on astronomic plates. But also many specific methods that must be developed for processing of plates.