TOPPED-Remove all pixel values above a certain limit from an NDF image file

Description:

Sets to bad, all the pixels with a count above the threshold level. An option allows the close neighbours of the bright pixel to be set to bad as well. Close neighbours are considered to be those pixels within a user defined radius of the bright pixel.

A further option allows all bad pixels in the output image to be assigned a random value. The values chosen are taken from a Normal distribution defined by the user.

Usage:

TOPPED IN OUT WIDTH BACK SIGMA NSIGMA NOISE PSIZE

Parameters:

BACK = _REAL (Read)

The background count value. Units counts.

IN = _NDF (Read)

The name of the NDF that is to be examined.

NOISE = _LOGICAL (Read)

Defines whether or not bad pixels should eventually be assigned a random value.

NSIGMA = _REAL (Read)

The number of standard deviations above sky at which the cutoff occurs.

OUT = _NDF (Write)

The name of the output NDF that will be created.

PSIZE = _REAL (Read)

The size of each pixel in arc seconds. If the image contains a SKY co-ordinate frame this value will be determined automatically.

SIGMA = _REAL (Read)

The background pixel count standard deviation value. Units counts.

WIDTH = _REAL (Read)

The width of the circle around a bright pixel within which pixels will be set to bad. Units arc seconds.

Examples:

topped in=eggs out=scrambled width=2.5 psize=0.44 back=1000.
     sigma=23. nsigma=8. noise=false

Uses EGGS as the input image and finds all pixels within the image that have a count greater than 1000.+8.x23. These are all set to the bad value. In addition, all pixels within a radius of 1.25 arc seconds are also set to bad.

topped in=objects out=cut width=4. back=6200. sigma=390.
     nsigma=10. noise=true

Uses OBJECTS as the input image and finds all pixels within the image that have a count value greater than 6200.+10.x390.. These are all set to random values, as are all the pixels within a radius of 2. arc seconds. Pixel size in arc seconds will be determined if possible from the WCS component of the image.

Notes:

The distribution of pixel values used when NOISE=TRUE comes from a Normal (Gaussian) distribution. In some circumstances, particularly for low count values, this may not be appropriate.