Bad data

Two methods are available for dealing with bad data. The magic value method uses special values stored within the data themselves to indicate that a datum is undefined or invalid. The second method is quality. Each data value may have associated with it a data-quality value, an 8-bit code which flags whether the data value is special in some way or combination of ways.

The NDF has a [BAD_PIXEL] flag, which allows applications to find out in advance if there are any magic-value data within the [DATA_ARRAY]. If not, a version of the algorithm which does not do the checks can be invoked, in order to save time. Note that in this document the term pixel is used in its generic sense, i.e. equivalent to an array element or bin, and therefore, pixel does not imply membership of a two-dimensional array.

Full details of bad-pixel methods are presented here.