Subtracts one NDF data structure from another
[!]
"Background subtracted"
. This routine correctly processes the AXIS, DATA, QUALITY, LABEL, TITLE, HISTORY, WCS, and VARIANCE components of an NDF data structure and propagates all extensions.
The UNITS component is propagated only if it has the same value in both input NDFs.
Processing of bad pixels and automatic quality masking are supported.
All non-complex numeric data types can be handled.
Huge NDFs are supported.