SAOimage display of M-51

SAOimage
as an IRAF display task

SAO/TDC Home Page
There are several advantages of using SAOimage directly to display images under IRAF rather than using it as an imtool and displaying with images.tv.display. You can see the exact value of each pixel rather than the 256-binned digitization you get from display. World coordinate system information, which allows you to track the cursor in sky coordinates, is not passed to SAOimage by display. Because SAOimage has full access to pixel values, rescaling can be done using cursor commands rather than having to redisplay using IRAF commands. The disadvantage is that you cannot use IRAF tasks such as imexamine to check out the image.

First make sure that IRAF thinks of SAOimage as an external task. The following line can be added to your login.cl file if saoimage is in the search path defined in your .cshrc file, which IRAF accesses before running external tasks using csh: 

task    $saoimage       = $saoimage
To absolutely define the pathname for such an external task, add either of the following lines instead, where the italicized material is replaced by the pathname on your computer: 
task    $saoimage       = "$"//osfn('saoimage IRAF pathname')
or 
task    $saoimage       = "$"//"saoimage full pathname"
The advantage of using an IRAF task to display images is that you can set frequently used parameters there, shortening the length of the command line you need to use. A simple CL task has been written to run SAOimage so image extensions and format arguments can be preset and the user doesn't have to worry about them each time an image is displayed.

The source code for the IRAF task, xdisp, which we use at the Center for Astrophysics Telescope Data Center is available. To use it, add the line 

task	xdisp		= tasks$xdisp.cl
to your login.cl, where the file xdisp.cl resides in the directory defined by the IRAF environment parameter tasks.

Last updated 8 July 2002 by Doug Mink dmink@cfa.harvard.edu