Francisco Valdes (IRAF Group/NOAO)
This paper presents two new algorithms used in the IRAF CCD Mosaic Reduction Package, MSCRED. However, these algorithms are not specific to mosaic data. The first algorithm uses photometry of common objects in multiple exposures to derive relative sky brightness and/or transparency differences. The second models and removes pupil ghost images. The algorithms are described and their application to NOAO CCD Mosaic Imager data illustrate their usage.