.help normflat Sep84 noao.imred.generic
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NAME
normflat -- Create a flat field by normalizing a calibration image
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USAGE	
normflat image flatfield
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PARAMETERS
.ls image
Calibration image to be used.
.le
.ls flatfield
Flat field to be created.
.le
.ls norm = INDEF
Normalization factor to be used if not INDEF.  If INDEF the normalization
factor is automatically determined.
.le
.ls minflat = INDEF
Minimum data value to be used in determining the normalization and in
creating the flat field.  Values less than or equal to this value are
replaced with a flat field value of 1.
.le
.ls sample_section = "[]"
Section of the image to be sampled in determining the normalization if
norm = INDEF.
.le
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DESCRIPTION
A flat field is created from a calibration image by normalizing the calibration
image.  The normalization is specified with the parameter \fInorm\fR.  If the
value of \fInorm\fR is INDEF then the normalization is determined by sampling
the pixels in the sample section with values greater than \fIminflat\fR.
This task differs from the task \fBnormalize\fR in that data values less
than or equal to \fIminflat\fR are replaced with unity in the normalized
flat field.
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EXAMPLES
To create a flat field from a calibration image "quartz" using pixels
above 1000 and selecting the normalization to be 3500:

	cl> normflat quartz flat norm=3500 minflat=1000

To determine a normalization from the pixels above 1000 and sampling
every fifth pixel in each dimension:

.nf
	cl> normflat quartz flat minflat=1000 sample=[*:5,*:5]
.fi
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SEE ALSO
normalize
.endhelp