Produces a flatfield calibration image
The input data are filtered in an attempt to remove any small blemishes etc. before combination. This is achieved by smoothing using a boxfilter and then comparing with the original data. An estimate of the standard deviation of each pixel from its surroundings is made. Pixels deviating by more than GAMMA standard deviations are rejected. This procedure is then iterated ITER times. In this way, all image features with a scale size comparable with, or smaller than, the smoothing area size are rejected.
"
TRIMMED"
[0.2] "
cleaning"
iteration is performed. [3.0]
GENVAR = _LOGICAL (Read)
Note that for this option to work well you should have many images and that any output pixels that only have one input image contributing to their value will have their variances set bad. [FALSE]
IN = LITERAL (Read)
The default for this parameter is TRUE and this cannot be overridden except by assignment on the command line or in response to a forced prompt. [TRUE]
If the logging system has been initialised using CCDSETUP then the value specified there will be
used. Otherwise, the default is "
CCDPACK.LOG"
. [CCDPACK.LOG]
TERMINAL – Send output to the terminal only
LOGFILE – Send output to the logfile only (see the LOGFILE parameter)
BOTH – Send output to both the terminal and the logfile
NEITHER – Produce no output at all
If the logging system has been initialised using CCDSETUP then the value specified there will be
used. Otherwise, the default is "
BOTH"
. [BOTH]
"
THRESH"
then this value defines the upper limit for values which can be used when combining the data. This
limit applies to the output data range. MEAN – Mean of the input data values
MEDIAN – Weighted median of the input data values
TRIMMED – An "
alpha trimmed mean"
in which a fraction alpha of the values are removed from
each extreme
MODE – An iteratively "
sigma clipped"
mean which approximates to the modal value
SIGMA – A sigma clipped mean
THRESHOLD – Mean with values above and below given limits removed
MINMAX – Mean with the highest and lowest values removed
BROADENED – A broadened median (the mean of a small number of central values)
FASTMED – Unweighted median of the input data values
[MEDIAN]
"
THRESH"
then this value defines the lower limit
for values which can be used when combining the data. This limit applies to the output data range. "
MODE"
. [7] "
MODE"
, "
SIGMA"
and "
CLIPMED"
methods. For METHOD = "
MODE"
the standard deviation is estimated
from the population of values. For METHOD = "
SIGMA"
and "
CLIPMED"
this value is
the pixel variance if one exists, otherwise one is etimated from the population of values.
[4.0] If a global value for this parameter has been set using CCDSETUP then that value will be used. [FALSE]
’
"
f1,f2,f3,f4,f5"
’
method=median out=mflat ^
flat_frames.lis
out=master_flat ’
flatr/∗’
out=’
flatr/master_flat’
gamma=2.5 iter=5 ’
ff*’
out=master_flat
gamma=10 iter=1 "
ff*"
are combined into a master flatfield.
Defect rejection is still performed but with gamma set so high and by performing only one
iteration almost no bad data will be detected. The data input into this routine should have bias strip regions and any badly vignetted parts removed.
The input images are normalised to have a mean of one before being combined. This makes sure that all input images contribute to the final result (even though, for instance, they were taken on a source of varying brightness, e.g. the twilight sky).
"
current"
value is the value
assigned on the last run of the application. If the application has not been run then the
"
intrinsic"
defaults, as shown in the parameter help, apply. The exceptions to this rule are:
TITLE – always "
Output from MAKEFLAT"
KEEPIN – always TRUE
Retaining parameter values has the advantage of allowing you to define the default behaviour of the application but does mean that additional care needs to be taken when using the application on new datasets/different devices, or after a break of sometime. The intrinsic default behaviour of the application may be restored by using the RESET keyword on the command line.
Certain parameters (LOGTO, LOGFILE and USESET) have global values. These global values will always take precedence, except when an assignment is made on the command line. Global values may be set and reset using the CCDSETUP and CCDCLEAR commands.
The routine supports BAD pixels and all data types except COMPLEX. All combinational arithmetic is performed using floating point. The AXIS and TITLE components are correctly propagated. The output is a ratio so the units are set to blank. The variances are propagated through the combination processing, assuming that the input data have a normal distribution.