Reducing a Bias

To reduce a BIAS, Portable--CGS4DR reads the raw data from store in $idir/ and FITS header information from store in $odir/, applies a bad pixel mask, writes the reduced data parameters into the index file and stores the reduced BIAS in $rodir/ as shown in figure .

  
Figure: Reducing a BIAS

Note that BIAS frames are not subtracted when data is taken in NDR (non-destructive read) mode---even if requested---since the NDR algorithm has already accounted for the bias level in the data.