Quick Notes on using IRAF to examine images.  (for AY192 problems)

To invoke IRAF you need a login.cl file in your directory (I usually 
put it all in a subdirectory called IRAF). You can get a copy of mine 
from the website (jph.login.cl) and place in in a subdirectory in your 
account in a file just called "login.cl." Type "cl" or "ncl" while you 
are in your iraf directory to get into the IRAF environment.  You'll be 
greeted by a bunch of information  and a list of the packages that are
loaded.  IRAF works by loading in various reduction packages.  These
include the "tv" package which, when loaded will allow you to display
images.   For the exercise here load tv and imred by simply typing
those package names.

You also need to set some environment variables and path's.  This is
what I have for IRAF in my .cshrc file:

# IRAF package
    setenv  iraf    /IRAF/iraf.solaris/
    set path=( $path /opt/IRAF/iraf.solaris/unix/bin.ssol )
    setenv  iraf    /IRAF/iraf/
    set path=( $path /opt/IRAF/iraf/unix/bin.sparc )
# If using FOCAS under the IRAF package, add following line
 set path=( $path /IRAF/iraf.bin.sparc/focas)

To display a file in IRAF I usually use SAOimage.    Open a image
display window with "simtool".  You will need to have set the
DISPLAY environment correctly if you haven't already done so
when logging on --- "setenv DISPLAY machine.name:0.0"  for example.
After you have an image display window  (you can also use ximtool),
type "display xxxx.imh"  to display image xxxx.

You can do image arithmetic using the imarith routines. For example,
"imarith image1 + image2 sum"   will add images 1 and 2 and put the
resultant image in "sum".  You can also combine sets of images
using the special arithmetic functions "imcombine", which allows
you to combine, say, BIAS frames via several different algorythims
such as avesigclip, minmax, crreject (cosmic ray reject), etc. 

The other routines you'll need to use are imstat, which will
calculate various properties of the images like means and standard
deviations (including clipping pixel values that are too high or low,
which you will need to do), and possibly imcopy, which will
allow you to copy files and also to trim them  (i.e. create new files
that only have the central, say, 500x500 pixels) using the image
section format.   

Manuals for all of these routines can be obtained by typing
"help packagename" in IRAF, or "help packagename | lpr"  if
you want a hardcopy.

Small details:  most unix commands also work directly in IRAF.
Your aliases and special commands will not.  If there is a normal
unix command that doesn't, try "! command" --- the "!" puts you back
into the cshell for one line.

There are many IRAF gurus and accolytes at the observatory, so it should
be raltively easy to find help.    You don't need to use IRAF for the
exercise if you already know another package like AIPS or IDL that
can perform the same functions.   Doug Mink (dmink@cfa)  is the chief
guru in the Telescope Data Center.  Iraf documentation can also be found
at the NOAO website.
 
JPH 12/31/99