If for some reason you cannot use `image' to display images, you can still display them as contour plots or as dithered grey plots. This works even when the display window has only two colours, say when you have a b/w X terminal. Like spectral plots, these plots go to the `soft' device.
ICL> icont a_file min max min max low=0 high=250 contours=6 accept
ICL> igrey a_file min max min max low=0 high=250 accept
If the display window has more than 16 colours, `igrey' will use those resources and display with true grey levels. It will also reset the window colours to grey. Well, strictly speaking the colours are not grey, but go linearly from the background colour to the foreground colour. If you choose pink and green for fore- and background, you can get quite a hideous composition.
FIGARO A general data reduction system