With a master bias

If you have made a master bias frame using MAKEBIAS then how you debias depends on how you made it. If your master bias has been combined to give a mean of zero then it will require offsetting to the `zero' level in the bias strips. DEBIAS will require the values of the rows or columns that the strip(s) are found within. You tell DEBIAS whether the values are rows or columns by specifying a ``readout direction'' `X' or `Y' (see Figure ). The bias strip ranges must be supplied in pairs; the column or row number on which it starts and the column or row number on which it ends. There are usually two strips on each side of the data, so this requires 4 values. If your data has three ``strips'' (probably as part of a region running around the data) then choose the two parallel ones (but make sure that the overscan strip, usually the one on the right, isn't contaminated by residual charge), if it has only one then the choice is obvious.

To subtract a zeroed master bias frame type something like:

% debias in='"rdata/*,ffr/*"' out='*_debias' bounds='[2,10,400,416]' rnoise=10
         adc=1 bias=master_bias

or conversely let DEBIAS prompt you. If you meet any questions which you do not understand hit return to accept the default, or respond with a `?' to get some help. If things are really bad then `!!' (abort) will always terminate the application immediately. (Note that ADC, BOUNDS and RNOISE need not be given if you've used CCDSETUP.)

If your master bias frame has a non zero mean (if you've selected the ZERO=FALSE option in MAKEBIAS) you just want to subtract it so use:

% debias in='"rdata/*,ffr/*"' out='*_debias' rnoise=10 adc=1 bias=master_bias
         offset=false

The ADC - analogue-to-digital conversion - factor is required to generate error estimates from the number of ADUs recorded in each pixel, as is the RNOISE value. To avoid this just use GENVAR=FALSE and leave out the ADC and RNOISE parameters.