pro display, data, z1, z2, bw
;
;  Program to display an image (stored in data)
;  z1 and z2 are lower and upper limits for stretch on display
;
np = n_params()
if np eq 0 or np gt 4 then goto, ERRMES
sz = size(data)
if sz(0) ne 2 then goto, ERRMES
grey = 1
if np eq 2 then begin
    grey = 0
    if z1 eq 'p' or z1 eq 'P' then grey = 1
    if z1 eq 'n' or z1 eq 'N' then grey = -1
    if grey eq 0 then goto, ERRMES
endif
if np le 2 then begin
    i1 = (sz(1)/2) - 16
    i2 = i1 + 32
    j1 = (sz(2)/2) - 16
    j2 = j1 + 32
    sub_rast = data(i1:i2,j1:j2)
    z1 = median(sub_rast) - (3. * stdev(sub_rast))
    z2 = median(sub_rast) + (3. * stdev(sub_rast))
    print,'Setting z1 =',z1, '        and      z2 = ', z2
endif
if np eq 4 then begin
    grey = 0
    if bw eq 'p' or bw eq 'P' then grey = 1
    if bw eq 'n' or bw eq 'N' then grey = -1
    if grey eq 0 then goto, ERRMES
endif
if z1 gt z2 then begin
    zt = z1
    z1 = z2
    z2 = zt
endif
;
window,0,xsize=450,ysize=300,title='Image'
if grey eq 1 then tvscl, data < z2 > z1
if grey eq -1 then tvscl, -data < (-z1) > (-z2)
; defsysv, '!neg', grey
; defsysv,'!neg', exists=i
; if i ne 1 then defsysv, '!neg', grey else !neg = grey
return
;
ERRMES:
print,' ERROR! Enter parameters as follows (items in parenthesis are optional)'
print,string(7B)
print,' display, data_array, (lower_display_lim, upper_display_lim), bw'
print,string(7B)
print,' '
return
end