REDUCE_FLAT - Reduces an imaging flat field

Description:

This reduces a flat field in the conventional manner consisting of bad-pixel masking, dark subtraction, and normalisation by the mean of the image. It also files the normalised flat-field frame for use by subsequent flat-fielding operations.

Notes:

• This recipe will reduce any image passed to it. Care must be taken to ensure that a proper flat-field image will be reduced.

• The bad pixel mask applied is $ORAC_DATA_CAL/bpm.

• The flat field is normalised using a clipped mean, where the clipping levels are 2, 3, and 3 standard deviationss. This value is effectively the mode of the image. The entire image is divided by this value to normalise it.

• Intermediate frames are deleted.

Output Data :

• The flat is called flat_<frame_number>.

• The flat is filed in $ORAC_DATA_OUT/index.flat.

Implementation Status:

• The processing engines are from the Starlink packages KAPPA and CCDPACK.

• Uses the Starlink NDF format.

• History is recorded within the data files.

• The title of the data is propagated through the intermediate file to the flat.

• Variance information is not supported.