normflat image flatfield
image
Calibration image to be used.
flatfield
Flat field to be created.
norm = INDEF
Normalization factor to be used if not INDEF. If INDEF the normalization
factor is automatically determined.
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.
sample_section = []
Section of the image to be sampled in determining the normalization if
norm = INDEF.
A flat field is created from a calibration image by normalizing the calibration image. The normalization is specified with the parameter norm. If the value of norm is INDEF then the normalization is determined by sampling the pixels in the sample section with values greater than minflat. This task differs from the task normalize in that data values less than or equal to minflat are replaced with unity in the normalized flat field.
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:
cl> normflat quartz flat minflat=1000 sample=[*:5,*:5]