1.4.5 Data Scaling

One of the features of FITS is that 2 keywords called BSCALE and BZERO (or TSCALn and TZEROn in the case of columns in a table) may be used to define a linear scaling factor and offset that should be applied to the raw data values in the FITS file. The FITSIO routines automatically check for the presence of these keywords and will by default apply this scaling to the data values as they are read before the values are passed to the application program. Similarly, FITSIO will transparently apply the inverse scaling when writing data to a FITS file.