PRO checkrat,year,month,day,hour,minute,second $
	    ,subtract=subtract,interactive=interactive

; All variables entered?
IF N_PARAMS() LT 6 THEN BEGIN
    PRINT,'Usage: checkrat,year,month,day,hour,nminute,second'
    RETURN
    ENDIF

; Open a plotting window
WINDOW,0,XSIZE=512,YSIZE=512
out=INTARR(512,256)

; load map of sky-viewing pixels
mask=BYTARR(128,128)
OPENR,sky,'~cnsr3/941202_0.sky',/GET_LUN
READU,sky,mask
FREE_LUN,sky

; load image lists
rdilist,2,year,month,day,hour,minute,second,n,t,f

; delete any calibration images from lists
keep=WHERE((STRPOS(f(0,*),'cal') EQ -1) AND $
           (STRPOS(f(1,*),'cal') EQ -1))
n=N_ELEMENTS(keep)
t=t(*,keep)
f=f(*,keep)

; locate first image pairs of cycles
t0=REFORM(t(0,*))
dt=(t0-SHIFT(t0,1))>0
cycle=[0,WHERE(dt GT 70),n]	; seems to work for 60-s images
cyclen=(SHIFT(cycle,-1)-cycle)
cyclen=cyclen(0:N_ELEMENTS(cyclen)-2)
cycle=cycle(0:N_ELEMENTS(cycle)-2)
ncycles=N_ELEMENTS(cyclen)

; for each camera, load all the images in the cycle
FOR ic=0,ncycles-1 DO BEGIN
    PRINT,STRSEC(t(0,cycle(ic)))
    nc=INDGEN(cyclen(ic))+cycle(ic)
    FOR cc=0,1 DO BEGIN
        fc=REFORM(f(cc,nc))	; names of Camera cc images in this cycle
        rdkimg,fc(0),hb,im,/verb,/nofix
        hbs=BYTARR(512,cyclen(ic))	; create header byte storage array
        hbs(0,0)=hb		; and store first image header bytes
        s0=SIZE(im)
        cols=s0(1)
        rows=s0(2)
        ims=INTARR(cols,rows,cyclen(ic)); create image storage array
        ims(0,0,0)=im		; and store first image
        FOR jc=1,cyclen(ic)-1 DO BEGIN
            rdkimg,fc(jc),hb,im,/verb,/nofix	; read succeeding images in cycle
            hbs(0,jc)=hb	; and store header bytes
            ims(0,0,jc)=im	; and images
            ENDFOR

; check that the first image was copied to all subsequent images
        FOR jc=0,cyclen(ic)-1 DO BEGIN
	    ndiff=LONG(TOTAL(ims(*,rows/4:rows-1,jc) $
			     NE ims(*,rows/4:rows-1,0)))
            IF ndiff GT 0 THEN $
		PRINT,ic,cc,jc,ndiff $
                     ,FORMAT='("Cycle ",I3,", camera ",I1,", image ",' $
			    +'I1," - image 0: ",I0," different pixels")'
            ENDFOR

; determine the average ratio between the third and first 630.0 nm images 
; (Camera 0 only)
        IF cc EQ 0 THEN BEGIN
            c0f2=WHERE(STRPOS(fc,'02060') NE -1,nc0f2)
            IF nc0f2 GT 1 THEN BEGIN
                IF KEYWORD_SET(subtract) $
                    THEN ims(*,*,c0f2(1))=ims(*,*,c0f2(1))-ims(*,*,c0f2(0))
                tmp=LONG(REBIN(REFORM(ims(*,0:rows/4-1,c0f2(1)),cols/2,rows/2) $
                              ,cols,rows,/SAMPLE))
		lim0=pcentile(ims(*,*,0),[0.01,0.99])
		lim2=pcentile(tmp,[0.01,0.99])
		hist0=[0L,HISTOGRAM(ims(*,*,0)*mask,MIN=1,BIN=1,MAX=lim0(1))]
		pv0=MAX(hist0,pk0)
		hist2=[0L,HISTOGRAM(tmp*mask,MIN=1,BIN=1,MAX=lim2(1))]
		pv2=MAX(hist2,pk2)
		PRINT,"Ratio of most probable values (2nd/1st) is " $
		     ,FLOAT(pk2)/pk0,FORMAT='(A,F5.3)'

                rat=FLOAT(tmp)/FLOAT(ims(*,*,0))
                rhist=[0L,HISTOGRAM(mask*rat,MIN=0.01,MAX=10,BIN=0.01)]
                mhist=MAX(rhist,loc)
                xlim=ROUND([loc/100.-1,loc/100.+1])
                xhist=FINDGEN(1001)*0.01
                fit=gaussfit(xhist,rhist,a)
                r=a(1)
                PRINT,"Most probable ratio (2nd/1st) is ",r $
                     ,FORMAT='(A,F5.3)'
                lims=pcentile(ims(*,*,0),[0.01,0.99])
                out(0,0)=ROTATE(REBIN(ims(*,*,0)>lims(0)<lims(1) $
                                     ,256,256,/SAMPLE) $
                               ,2)
                out(256,0)=ROTATE(REBIN(FLOAT(tmp/r)>lims(0)<lims(1) $
                                       ,256,256,/SAMPLE) $
                                 ,2)
                TVSCL,out,0
		IF KEYWORD_SET(interactive) THEN STOP
                ENDIF
            PRINT,FORMAT='()'
            ENDIF

        IF KEYWORD_SET(interactive) THEN BEGIN
            READ,'Press any key to continue.'
            k=GET_KBRD(1)
            ENDIF

        ENDFOR
    ENDFOR

RETURN
END