SAOimage, M.VanHilst(1990), Bulletin of the American Astronomical Society, Vol. 22, p.935.


Smithsonian Astrophysical Observatory

This report covers the period through January 1990.


SAOimage (pronounced S-A-0-image), is an X windows-based interactive program to display astronomical image data on a workstation screen. SAOimage was developed by the author and funded by NASA as part of the Smithsonian Astrophysical Observatory's PROS analysis software package for the U.S. ROSAT Science Data Center. It can run either stand-alone, reading FITS (SIMPLE=T), IRAF (.imh), and array image files directly, or be connected to IRAF, emulating NOAO's imtool, for interactive image display and analysis. Originally developed for X10, under the name "ximage", SAOimage now uses X1l and compatible display servers and runs under UNIX (SYSV and BSD) or VMS. (The VMS port was done by Jay Travisano of the Space Telescope Science Institute.)


SAOimage concentrates on display features, leaving image analysis to other programs. Within its workstation window, it provides a large display area, a magnifier subwindow, a pan and zoom guide, a color bar, and a button control panel. A pop-up editor facilitates setting parameters and entering new image files. On color workstations (with 32 or more colors), a directly manipulable color table graph can be popped up. For workstations without color, halftone display modes are also supported.

The SAOimage user interface was designed to be easy to learn and use. With the mouse, the user can manipulate the color map, pan and zoom the image, and outline regions of interest. By making selections on the button menu, the user can rescale the image, select a different color palette, specify the region shape, dispatch a hardcopy to the printer, or specify the mode of mouse control. Various optimizations have been used to make the response to user commands fast and fluid.


To display data, with a large range of values, within the range of available display colors, SAOimage provides five different modes of scaling; linear, wrapped linear, geometric (root), exponential (log), and histogram equalization. By adjusting the scaling window, selecting the scaling mode, and possibly adjusting the weighting parameters, structural features in the image data can be made apparent, even on halftone monitors.

Several shapes are provided for outlining regions of interest. These include points, arbitrary polygons, rotatable boxes and ellipses, and annuli (circular, elliptical, and rectangular). Regions can be written to and read from ASCII disk files. The PROS IRAF tasks can read these ASCII files to make image masks and perform various spatial analyses.

SAOimage can display a continuous readout of the pointer coordinates and the corresponding pixel value, or display a table of pixel values within a small square. The pointer position and surrounding image can be continuously displayed in the magnifier subwindow.

For color workstations, several default colormaps are provided. The colormap can be interactively stretched and shifted, and the colormap table can be directly manipulated. Colormap tables can be written to and read from ASCII disk files. An additional mode of manipulation allows gamma adjustment of colors. For halftone display, matrix dithering and error diffusion are both supported.

Because it uses Xll for the display, SAOimage itself can be running on one machine while the display and user interface are on a different machine or terminal (nearby or far away).


Users who intend to use SAOimage with IRAF should request it from NOAO when they request IRAF. Others can obtain source code from the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. Executables for many common machines are also available. SAOimage has compiled and run successfully on Convex, DG Aviion, DECstation, VAXstation (Ultrix 3.x and VMS 5.x), Sun-3, Sun-4, Sun-386i, and many HP and HP-Apollo machines.

For users with access to Internet, source code and executables can be copied from ( via anonymous ftp. Large files may be compressed, requiring UNIX uncompress or Zcat to decompress them.

For more information about SAOimage, please contact us at the following address:


 Smithsonian Astrophysical Observatory
 attn. Mike VanHilst MS 3
 60 Garden Street
 Cambridge, MA 02138

 e-mail: (Internet)
 mvh@cfa (Bitnet)
M. VanHilst Harvard-Smithsonian Center for Astrophysics
now Computer Science Department, University of Washington

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