Data Reduction Frequently Asked Questions
How do I uncompress .fz files?
VISTA/VIRCAM data are compressed with Rice lossless compression algorithm. This is one of the standard compression algorithms and more details can be found here: http://heasarc.gsfc.nasa.gov/fitsio/fpack/.
If you display images using ds9, there is no need to uncompress them, because ds9 (as well as CFITSIO) supports this format.