ALPHA = _REAL (Read)
The fraction of extreme values to remove before
combining the data at any pixel. This fraction is removed from each extreme so can only take a value
in the range 0 to 0.5. Only used if METHOD="
TRIMMED"
[0.2]
BOXSIZE(2) = _INTEGER (Read)
The X and Y sizes (in pixels) of the rectangular box to be applied to smooth the input images. If only a
single value is given, then it will be duplicated so that a square filter is used. The values given will be
rounded up to positive odd integers if necessary. The values should be adjusted to be larger than the
size of any expected defects. [15,15]
CLEAN = _LOGICAL (Read)
Whether or not to
attempt to clean the input images of any defects. For some data types (i.e. spectra) small scale
strutures and sharp edges may be real and can be protected against removal by setting
this parameter FALSE. [TRUE]
GAMMA = _REAL (Read)
The number of standard
deviations by which a value has to deviate from the local mean (defined by the mean within a
box of BOXSIZE(1) by BOXSIZE(2) pixels) before it is considered to be in error. Aberrant
pixels are removed from the data before the next "
cleaning"
iteration is performed. [3.0]
GENVAR = _LOGICAL (Read)
If TRUE and USEVAR is also FALSE, then “variances” for the output
image will be generated using the natural variation in the input images. These values can be used to
estimate the quality of the output flatfield.
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)
A list image names. These contain the flatfield data. The image names should
be separated by commas and may include wildcards.
ITER = _INTEGER (Read)
The number of
defect rejecting iterations. [3]
KEEPIN = _LOGICAL (Read)
Whether to keep (i.e. not delete) the
input images or not. Deleting the input images has the advantage of saving disk space, but should
probably only be used if this program is part of a sequence of commands and the intermediary data
used by it are not important.
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]
LOGFILE = FILENAME (Read)
Name of
the CCDPACK logfile. If a null (!) value is given for this parameter then no logfile will be written,
regardless of the value of the LOGTO parameter.
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]
LOGTO = LITERAL (Read)
Every CCDPACK application has the ability to log its output for future reference as well as for display
on the terminal. This parameter controls this process, and may be set to any unique abbreviation of the
following:
-
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]
MAX = _REAL (Read)
If METHOD = "
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.
METHOD = LITERAL (Read)
The method to be used to
combine the data components of the input images. This may be set to any unique abbreviation of the
following:
-
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)
- CLIPMED – A
sigma clipped median
-
FASTMED – Unweighted median of the input data values
See also “
Image combination
techniques”.
[MEDIAN]
MIN = _REAL (Read)
If METHOD = "
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.
MINPIX = _INTEGER (Read)
The minimum number of good (ie. not BAD) pixels required which are
required to contribute to the value of an output pixel. Output pixels not meeting this requirement are
set BAD. [1|2]
NITER = _INTEGER (Read)
The number of refining iterations performed if
METHOD = "
MODE"
. [7]
NORM = _LOGICAL (Read)
Whether to normalise the output NDF to
have a mean of one. [TRUE]
OUT = LITERAL (Write)
Name of an image to contain the
output flatfield data. Note this image will have a precision of at least _REAL. If USESET is
true and multiple Sets are represented in the IN list then this name will be used as the
name of an HDS container file containing one NDF structure for each Set Index value.
This name may be specified using indirection through a file. [TRUE]
SIGMAS = _REAL
(Read)
Number of standard deviations to reject data at. Used for "
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]
USESET = _LOGICAL (Read)
Whether to use Set header information or not. If
USESET is false then any Set header information will be ignored. If USESET is true, then
input files will be considered in groups; a separate flatfield will be constructed for each
group of corresponding input frames (i.e. those sharing the same Set Index attribute). If this
results in multiple output flatfields, they will be written as separate NDF structures into a
single HDS container file. If no Set header information is present in the input files, then
flatfielding is done on all the input files together, so USESET can usually be safely set to
TRUE.
If a global value for this parameter has been set using CCDSETUP then that value will be used.
[FALSE]
USEVAR = _LOGICAL (Read)
If TRUE and all the input images contain error information
(variances), then these will be used as weights during image combination and will be propagated to
the output image. [TRUE]
TITLE = LITERAL (Read)
Title for the output image. [Output from
MAKEFLAT]
Most parameters retain their current value as default. The
"
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:
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.