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Purpose of the Quality Component  

The quality component of an NDF is provided to allow individual pixels to be flagged as having certain properties which applications may wish to take into account when processing them. In general, these properties are expected to be of a binary or logical character, such as membership of a set, rather than being quantitative, although combining several binary values to construct a simple numerical scale is not excluded.

To give a simple practical example, it might be useful to flag all the pixels in an image which are contaminated by defects in the detector system from which it originates. It might also be useful to classify each pixel as lying either in the ``sky'' background, or in the observed ``object''. Armed with this sort of information, it then becomes possible to perform operations like:

An NDF's quality component allows up to eight such binary conditions to be flagged, so numerous other applications and possibilities obviously exist.

If this appears too complicated for the sort of work you have in mind, then the good news is that the quality component can be almost entirely ignored by most applications and the default action of the NDF_ system will take care of it automatically. However, for applications which wish to exploit the possibilities that the quality component offers, a set of NDF_ routines is provided to access and control it explicitly. Their use is described here.



next up previous
Next: Accessing the Quality Array Directly
Up: THE QUALITY COMPONENT IN MORE DETAIL
Previous: THE QUALITY COMPONENT IN MORE DETAIL


Starlink User Note 33
R.F. Warren-Smith
11th January 2000
E-mail:rfws@star.rl.ac.uk

Copyright © 2000 Council for the Central Laboratory of the Research Councils