pro  vmg_flat, files, vflat, jflat
;+
; NAME: VMG_FLAT
; PURPOSE:   Produced the flat patterns for VMG observations
; INPUT: 
;        files     an array of V  and J file names
;                  files(*,0)       V files
;                  files(*,1)       J files 
; OUPUT:
;         vflat      a flat pattern for V images
;         jflat      a flat pattern for J images
;
; RESTRICTION:
;          Each pair of V files and J files should taken from
;          the same integration.         
; HISTROY:
;      August 1998 J. Chae
;-



nf = n_elements(files(*,0))

a=replicate(0., 512, 512, nf)
x1=16 & x2 = 505 & y1 =5 & y2=470
dy=15
mm = 0.
for k=0,  nf -1 do begin
tmp = readfits(files(k,0), /sil)
m=median(tmp)
mm=mm+m
tmp  = (tmp-m) 
a(x1:x2, y1+dy:y2+dy, k) = (tmp)(x1:x2, y1:y2)
tvscl, a(*,*,k)>(-100)<100
endfor   

tmp=fltarr(512, 512)
for x=x1, x2 do for y=y1, y2 do tmp(x, y, *) = median(a(x, y+dy, *)) 
tmp1=congrid(tmp(x1:x2, y1:y2), 200, 200, /interp)
get_bg, tmp1, bg,  $
        region=where(abs(tmp1) le 20),  degree=2
bg=congrid(bg, x2-x1+1, y2-y1+1, /interp)

for k=0, nf-1 do begin
a(x1:x2, y1+dy:y2+dy, k) = a(x1:x2, y1+dy:y2+dy, k) -bg
a(*, *, k)=a(*,*,k)>(-10)<10
tvscl, a(*,*,k)
endfor

mm=mm/nf
vflat=fltarr(512, 481)
vflat(x1:x2, y1:y2)=$
    (gaincalib(a, x0, y0, add=1, shift=1))(x1:x2, y1+dy:y2+dy)
vflat(x1:x2, y1:y2) = ringfilter(vflat(x1:x2, y1:y2),0,2)+bg
vflat=vflat+mm

a=replicate(1., 512, 512, nf)

for k=0,  nf -1 do begin
tmp = readfits(files(k, 1), /sil)
m=float(median(tmp))
tmp  = tmp/m 
a(x1:x2, y1+dy:y2+dy, k) = (tmp)(x1:x2, y1:y2)
endfor   
c=total(a(x1:x2, y1+dy:y2+dy, *), 3)/n_elements(a(0,0,*))
get_bg, c, bg, degree=2
for k=0, nf-1 do begin
a(x1:x2, y1+dy:y2+dy, k) = a(x1:x2, y1+dy:y2+dy,k)/bg
tvscl, a(*,*,k)>0.8<1.2
endfor
jflat = (gaincalib(a, x0, y0))
jflat(x1:x2, y1+dy:y2+dy) = jflat(x1:x2, y1+dy:y2+dy)*bg

jflat = jflat(0:511, dy:dy+480)

end