The background image subtraction step has two optional arguments, both of
which are used only when the step is applied to non-WFSS exposures.
They are used in the process of creating an average background image, to
control the sigma clipping, and are passed as arguments to the astropy
The number of standard deviations to use for the clipping limit. Defaults to 3.
The number of clipping iterations to perform, or
Noneto clip until convergence is achieved. Defaults to