Several different display servers, including SAOimage, SAOtng (the next generation of SAOimage), and Ximtool, can be used with IRAF. SAOtng may be retrieved via anonymous FTP from sao-ftp.harvard.edu in the directory ~ftp/pub/rd. Ximtool may be retrieved via anonymous FTP from iraf.noao.edu in the directory ~pub/v2103-beta. Ximtool is particularly handy if you want to blink images.
tv> display fname.c0h 1 (GEIS group 2)Note that when using display or any other task on GEIS images, you do not need to specify a group; the first group is the default. However, when working with FITS files you must specify an extension, unless the FITS file contains only a single image in the primary data unit and has no extensions. Figure 3.2 shows how to display group two of a WF/PC-1 image .
tv> display fname.fits 1 (FITS extension 11)
tv> display fname.fits[sci,3] 1 (FITS extension sci,3)
If you want to display all four chips of a WF/PC-1 or WFPC2 image simultaneously, you can create a mosaic with the STSDAS wmosaic task in the
hst_calib.wfpc package. Type help wmosaic for details.
Figure 3.2: Displaying an Image
Modifying the Display
There are two ways to adjust how your image is displayed:
The example in Figure 3.2 shows how you should display an image for a first look. By default, display automatically scales the image intensity using a sampling of pixels throughout the image. During your first look, you may want to experiment with the scaling using the zscale, zrange, z1 and z2 parameters. The zscale parameter toggles the autoscaling. Setting zscale- and zrange+ tells the task to use minimum and maximum values from the image as the minimum and maximum intensity values. To customize your minimum and maximum intensity display values, set zscale-, zrange-, z1 to the minimum value and z2 to the maximum value that you want displayed. For example:
im> disp w0mw0507v.c0h 1 zrange- zscale- z1=2.78 z2=15.27Notice in Figure 3.2 that when you run display, the task shows you the z1 and z2 values that it calculates. You can use these starting points in estimating reasonable values for the minimum and maximum intensity display parameters.1
If you want to display an image with high dynamic range, you may prefer to use logarithmic scaling. However, the log scaling function in SAOimage divides the selected intensity range into 200 linearly spaced levels before taking the log. The resulting intensity levels are rendered in a linear rather than logarithmic sense. You can often obtain better results if you create a separate logarithmic image to display. One way to create a logarithmic image is with the imcalc task:
im> imcalc x2ce0502t.c1h x2ce0502t.hhh "log10(im1+1.0)"If the peak pixel in your original image contained 2000 counts, for example, you would then display the logarithmic image with z1=0 and z2=3.3.
tv> display image.hhh[101:200,*] 1To specify the same pixel range in the second SCI extension of a NICMOS FITS image, you would use a command such as:
tv> display image.fits[sci,2][101:200,*] 1
If you specify both a group and an image section of a GEIS file, the group number must come first. When displaying sections of STIS and NICMOS FITS images, you must specify the extension, and the extension designation must come first.
Figure 3.3: Displaying Sections and Groups of an Image
firstname.lastname@example.org Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved. Last updated: 11/13/97 16:26:00