View a FITS image with a ds9 gui. The image is (1) displayed in a user-specified image frame, (2) "zoomed to fit", and (3) scaled between user-specified z1,z2 greyscale levels. If the values of z1,z2 are both "n", then the scaling is performed using the image minmax.

ds9_view ./t1.fits -1.0 1000.0 1   

Here are some ways to get better grey-scale levels:
ds9_view ./t1.fits minmax n 2   
ds9_view ./t1.fits zscale n 4   
(Notice that I used different farme numbers here! 

Usage: ds9view a.fits 1.0 2000.0
arg1 - names of fits image to be viewed
arg2 - low display level (z1)
arg3 - high display level (z2)
arg4 - frame number to be used 
z1,z2= (minmax n) or (zscale n) will work