saltflat

Name

saltflat – Flatfield correct SALT images

Usage

saltflat images outimages outpref flatimage (minflat) (clobber) (logfile) (verbose)

Parameters

images

String. List of input images including, if necessary, absolute or relative paths to the data. Data can be provided as a comma-separated list, or a string with a wildcard (e.g. ‘images=S20061210*.fits’), or a foreign file containing an ascii list of image filenames. For ascii list option, the filename containing the list must be provided preceded by a ‘@’ character, e.g. 'images=@listoffiles.lis‘.

outimage

String. A list of images. Data can be provided as a comma-separated list, or a string with a wildcard (e.g. ‘outimages=rS20061210*.fits’), or a foreign file containing an ascii list of image filenames. For ascii list option, the filename containing the list must be provided preceded by a ‘@’ character, e.g. 'outimages=@listoffiles.lis‘. This list must be of the same size as the images argument list.

outpref

String. If the outpref string is non-zero in length and contains characters other than a blank space, it will override any value of the outimages argument. Output file names will use the name list provided in the images argument, but adding a prefix to the basename of each output file defined by outpref. An absolute or relative directory path can be included in the prefix, e.g. ‘outpref=/Volumes/data/p’.

flatimage

String. File to use for flatfielding the data. This file should be the same format and size of the input data. The file will be normalized by the task prior to applying to the data.

minflat

Real. Minimum value for the flatfield image. Any pixels above this value will be replaces with this value.

clobber

Hidden boolean. If set to ‘yes’ files contained within the outpath directory will be overwritten by newly created files of the same name.

logfile

String. Name of an ascii file for storing log and error messages written by the task. The file may be new, or messages can also be appended to a pre-existing file.

(verbose)

Boolean. If verbose=n, log messages will be suppressed.

Description

SALTFLAT corrects a SALT image for flatflied variations.

The task reads in the flatfield image, flatimage. The flatimage will have any bad pixels below the minflat value replace by the minflat value. Then, the image will be normalized by its mean.

After normalizing the flatimage, SALTFLAT will divide flatimage into each of the images supplied here. If the images have variance frames, SALTFLAt will also propogate the errors through to the variance frames.

If the users wishes to only correct for pixel to pixel variations or illumination corrections, these images can be applied here but the flatimage would have to be prepared prior to running this task.

Examples

1. To flat field correct a SALT image:

   --> saltflat images='@images.lis' outimages='' outpref='f'
   flatimage='FLAT.fits' minflat=1 clobber='yes'
   logfile='salt.log' verbose='yes'

Time and disk requirements

Individual unbinned full frame RSS image files can be 112MB in size. It is recommended to use workstations with a minimum of 512MB RAM. On a linux machine with 2.8 Ghz processor and 2 Gb of RAM, one 2051x2051 image can be processed in 0.31 sec.

Bugs and limitations

SALTFLAT will only correct by the image given to it and no other process is applied to the data. SALTFLAT will not check to make sure that the data are the right type, but will blindly apply the correction.

Send feedback and bug reports to salthelp@saao.ac.za

See also

saltclean saltslot