10 Displaying Images

Having converted the images to the NDF format it is usually sensible to have a look at them before you proceed with the reductions. Any gross defects in the data will often be readily apparent and a quick check before you start may save you a great deal of wasted effort. Similarly, it is often prudent to display intermediate images created during the reductions to check that nothing has gone awry.

Several image display programs are available. One of the simplest to use, yet most powerful and flexible, is GAIA (see SUN/214[11]), which will be used in this recipe. Proceed as follows.

(1)

Move to subdirectory targets.

(2)

Start GAIA by typing:

  % gaia &

The ampersand (‘&’) is, of course, simply to run GAIA as a detached process, so that you can continue to issue Unix commands from the command line. The GAIA window should appear. Load file ngc2336_r_2.sdf by clicking the File menu (rightmost of the options in the menu bar at the top of the window), selecting Open… and using the file-picker which appears to choose the appropriate file.

(3)

The file should open, but the main display window will probably be mostly dark, with just a few white dots corresponding to the brightest parts of the image. Set some of the display options as follows:

(a)

click the Auto Cut: button for 90% (in the bottom right of the control panel in the centre top of the window),

(b)

click the View menu (second left in the menu bar at the top of the window), select Magnification and set it to 1/2x,

(c)

click View again, select Colors… (sic) and choose the heat colour table.

The display should now look something like Figure 10.

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Figure 10: An unprocessed R band image of NGC 2336 displayed with GAIA. The apparently asymmetric positioning of the image in the GAIA windows is caused by the bias strips along some of the edges of the CCD frame which appear black in this plot

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(4)

GAIA has many other functions and options and you may want to spend a while exploring some of them. On-line help is available from the Help menu at the extreme right of the menu bar at the top of the window. Similarly, you might also like to examine the other target image and the flat field and bias frames included in the example.

(5)

When you have finished close GAIA by clicking on the File menu and choosing the Exit option.