You can contour any given image by typing:
IDL> contour,image
IDL> contour, data(*,*,0)
IDL> contour, image, levels=[l1,l2,l3,...,ln]
where 
defines the contour levels you want to plot.
levels is an optional parameter which IDL will
choose for you if you omit them. You can overplot a contour on an
image by using OCONTOUR in the same way.