PRO bitdist,orb,id

path=-1
REPEAT BEGIN
    path=path+1
    rdimg,path,orb,id,header,img
    s=SIZE(img)
    n=s(s(0)+2)
ENDREP UNTIL (n GT 1) OR (path EQ 2)

IF n LE 1 THEN RETURN

TVSCL,img
PRINT,'Do you want to select a region of interest in the image? (Y/[N])'
resp='' & READ,resp
IF STRUPCASE(resp) EQ 'Y' THEN BEGIN
    r=DEFROI(s(1),s(2),0,0)
    img=img(r)
    n=N_ELEMENTS(r)
ENDIF

b=INTARR(8)
sb=b
h=HISTOGRAM(img,MIN=0,BIN=1,MAX=255)
FOR j=0,255 DO BEGIN
    FOR k=0,7 DO sb(k)=(j AND 2^k)/2^k
    b=b+h(j)*sb
ENDFOR
b=1.*b/n

PLOT,b,XTITLE='Bit Number (MSB=7)',YTITLE='Fraction of Pixels where Bit Set' $
    ,TITLE=STRING(orb,id,FORMAT='("Orbit ",I3,", Image ",F6.3)') $
    ,PSYM=10,XRANGE=[7.5,-0.5],XSTYLE=1,YRANGE=[0,1]
PLOTS,[-0.5,0.0],[b(0),b(0)]
PLOTS,[7.0,7.5],[b(7),b(7)]

multi=(!P.MULTI(1) GT 0) OR (!P.MULTI(2) GT 0)
csz=1./(1+multi)

sb=INTARR(8)
ssb=sb
width=9+8*(id gt 23)
sh=SMOOTH(h,width)
FOR j=0,255 DO BEGIN
    FOR k=0,7 DO ssb(k)=(j AND 2^k)/2^k
    sb=sb+sh(j)*ssb
ENDFOR
sb=1.*sb/n

OPLOT,sb,PSYM=10,LINESTYLE=1
PLOTS,[-0.5,0.0],[sb(0),sb(0)],LINESTYLE=1
PLOTS,[7.0,7.5],[sb(7),sb(7)],LINESTYLE=1

gh=(b GT sb)
XYOUTS,BINDGEN(8),b-0.03+0.04*gh,STRING(b,FORMAT='(F5.3)') $
      ,ALIGNMENT=0.5,CHARSIZE=csz
PLOTS,[7.0,6.5],[0.93,0.93]
XYOUTS,6.4,0.92,'Bit distribution of raw image',CHARSIZE=csz

XYOUTS,BINDGEN(8),sb+0.01-0.04*gh,STRING(sb,FORMAT='(F5.3)') $
      ,ALIGNMENT=0.5,CHARSIZE=csz
PLOTS,[7.0,6.5],[0.88,0.88],LINESTYLE=1
XYOUTS,6.4,0.87,CHARSIZE=csz,'Histogram smoothed by running'
XYOUTS,6.4,0.84,CHARSIZE=csz,STRING(width,FORMAT='(I2,"-DN boxcar")')

spike=FIX(ALOG(width)/ALOG(2))+1
ape=TOTAL((sb(0:spike-2)-b(0:spike-2))*2^BINDGEN(spike-2))
pds=(sb(spike)-0.5*(sb(spike+1)+sb(spike-1)));-(b(spike)-0.5*(b(spike+1)+b(spike-1)))
ape=ape+pds*2^spike
room=N_ELEMENTS(WHERE(b GT 0.2))-1
XYOUTS,room,0.1,'Average probable error due',CHARSIZE=csz
XYOUTS,room,0.07,CHARSIZE=csz $
      ,'to sticky bit = '+STRING(ape,FORMAT='(F4.1)')+' DN'

stop
RETURN
END