Image processing of digitized spectral data

Every observatory has a library of old pictures taken by photographic cameras. These measurements are not as such high quality as those from modern CCD systems, but could contain important data about rare phenomena or source data for long-period investigations (e.g., concerning the solar cycle). This paper presents methods for converting photographic images, collected at the Large Solar Vacuum Telescope (Baikal Astrophysical Observatory) to digital images, similar to CCD pictures. Special algorithms were used for this task and have been implemented in the IDL environment. The results of processing real spectral data and a comparison of processed photographic images and images taken with a TEK CCD are presented.