PRO oldmbkgrd,filename,hh,mm,ss,span,minim,pixchg,rutsec,exp=exp

COMMON header,fname,hbytes,nimages,utsec,exptimes,keep

IF NOT KEYWORD_SET(exp) THEN exp=60. ELSE exp=FLOAT(exp)

IF (N_ELEMENTS(fname) EQ 0) OR (fname NE filename) THEN BEGIN

; Open the file as a series of small (header-size) units and get
; the header information

    fname=filename

    OPENR,hbunit,filename,/GET_LUN
    hbfile=ASSOC(hbunit,BYTARR(512))

    hbstat=FSTAT(hbunit)
    hbbytes=hbstat.SIZE
    nimages=hbbytes/66048L
    PRINT,'There are '+STRTRIM(nimages,2)+' images'
    hbytes=BYTARR(512,nimages)
    utsec=LONARR(nimages)
    exptimes=FLTARR(nimages)

    FOR i=0L,nimages-1 DO BEGIN
        hbytes(0,i)=hbfile(129*i)
        header=gethd(hbytes(*,i))
        utsec(i)=3600L*header.misc.tm.hour $
	       + 60L*header.misc.tm.minute $
	       +  1L*header.misc.tm.second
        exptimes(i)=header.misc.exp_scale*header.exp.exposure/1000.
        IF (i GT 0) AND (i MOD 20 EQ 0) THEN PRINT,i,FORMAT='(I4,$)'
        IF (i GT 0) AND (i MOD 400 EQ 0) THEN PRINT,FORMAT='()'
        ENDFOR
    PRINT,FORMAT='()'
    CLOSE,hbunit
    FREE_LUN,hbunit

    ENDIF

minim=INTARR(256,256)+16383

butsec=3600L*hh+60L*mm+1L*ss
eutsec=ROUND(butsec+FLOAT(span)*3600)

OPENR,unit,filename,/GET_LUN
files=ASSOC(unit,BYTARR(66048))

keep=WHERE(exptimes eq exp)  

IF keep(0) EQ -1 THEN BEGIN
  exp=STRTRIM(exp,2)
  MESSAGE,'This file does not contain any '+exp+' second exposure images!',$
	  /INFORMATIONAL
 
  minim=-1
  pixchg=-1
  rutsec=-1
  RETURN
ENDIF ELSE BEGIN

rutsec=utsec(keep)
nimages=N_ELEMENTS(rutsec)

nhh=hh & nmm=mm & nss=ss

start=MIN(WHERE(rutsec GE butsec,any_images))
note=butsec-MIN(rutsec)
flag=eutsec-MAX(rutsec)
IF any_images NE 0 THEN BEGIN
   finish=MAX(WHERE(rutsec LE eutsec,number))
  IF note LT 0 THEN BEGIN
     start=0
     nhh=rutsec(0)/3600L
     nmm=(rutsec(0)-nhh*3600L)/60L
     nss=(rutsec(0)-nhh*3600L-nmm*60L)
     print,'The file chosen does not contain the start time requested.'
     print,nhh,nmm,nss,FORMAT='("The actual start time is ",I2.2,":",I2.2,":",I2.2,1X,"UT.")'
     ENDIF
 IF flag GT 0 THEN BEGIN
   finish=nimages
   print,'The file chosen does not span the time interval requested.'
   ehh=rutsec(finish-1)/3600L
   emm=(rutsec(finish-1)-ehh*3600L)/60L
   ess=(rutsec(finish-1)-ehh*3600L-emm*60L)
   print,nhh,nmm,nss,ehh,emm,ess,$
   FORMAT='("The file spans ",2(I2.2,":"),I2.2," to ",2(I2.2,":"),I2.2," UT.")'
  ENDIF
  pixchg=FLTARR(finish-start) 

  FOR i=start,finish-1 DO BEGIN
  
    file=files(keep(i))
    im=BYTE(file,512,256,256)
    ; If file was renormalized to fit 8 bits, reverse this.
     IF file(290) GT 0 THEN BEGIN
      IF file(291) EQ 1 THEN im=LONG(im)*(2^file(290))
      IF file(291) EQ 0 THEN im=LONG(im)*file(290)
     ENDIF

    wless=WHERE(im LT minim,count)
    
    IF wless(0) GE 0 THEN minim(wless)=im(wless)
    pixchg(i-start)=count
    ;stop
   ENDFOR
   rutsec=rutsec(start:finish-1)
   ENDIF ELSE BEGIN
     MESSAGE,'The file chosen does not contain any images from the time requested.',$
	     /INFORMATIONAL
     minim=-1
     rutsec=-1
     pixch=-1
     RETURN 
     ENDELSE

FREE_LUN,unit

ENDELSE
RETURN
END