Colraf: making colour astronomical images
Earlier this year I put together a few scripts that takes rgb FITS files and makes nice colour images. This was completed as part of development of tools for the University of Birmingham Observatory. Anyway, I meant to make this available before but I didn’t have the chance to make it friendly. Its quite simple to use but requires the user has [IRAF] installed. Examples of the images this script produces can be found on my flickr pages, but here is one for starters:
Getting the scripts: [colraf.tar.gz] (version 1)
Using the scripts:
Before running anything you must ensure that you have IRAF installed correctly and that you edit your LOGIN.CL file such that it expects to use FITS files, essentially uncomment the set imtype parameter:
set imtype = “fits”
Before running the task you should make sure that the images have names of a certain format. Flats need to have FLAT, darks need to have DARK and bias images should be prefix by bias (see the wast1.cl script for more info). The colour images have to have RED, GREEN and BLUE in them. You can use to help with the organisation.
Then you need to run:
The purpose of this is to do preliminary work on images before running IRAF. Firstly it will ask you for your reference image. Give the fits file. It will then open an editor (it uses pico but you can easily change this to use another) asking you to put in the coordinates of some reference stars that you can see in all filters (you need to give x,y pixels with a space in between – you need at least 3 positions).
This will open up and xgterm window.
Once open you need to run the first iraf script, like so:
cl < wast1.cl
Purpose: To make combined, dark / bias images and remove these along with the master flat field off images taken at the observatory.
xzap (inlist=@zapin,outlist=@zapout, zboxsz =5, nsigma = 4, nrings =2, nnegsig=0, nobjsig=2, skyfilt=15, skysubs=1,deletem=yes,statsec=, cleanpl=yes, cleanim=yes,verbose=no,checkli=yes)
cl < wast2.cl
Purpose: aligns and combines the images, finally making a colour composite and deletes junk files and puts the files into “original and final”.
This post was last updated on 9/02/2010 to add some bits and pieces to the documentation that was missing.