PRO starmag,img,col,row,diff
;program to find the DN of a star with respect to the median background
i=intarr(256,256)
row=REPLICATE(256.,N_ELEMENTS(row))-row
i(col,row)=1 ; binary image of stars
cell=INTARR(13,13)+1
cell(0:2,0:2)=0
cell(10:12,10:12)=0
cell(10:12,0:2)=0
cell(0:2,10:12)=0
di =DILATE(i,cell)
dimg=di*img ; image of areas around (col,row) of size 'cell' 
nbhd=INTARR(13,13,N_ELEMENTS(row))
diff=FLTARR(N_ELEMENTS(row)) & tot=diff & meandiff=diff

;calculating median BG and difference between BG and original image for each pt.
FOR j=0,N_ELEMENTS(row)-1 DO BEGIN
	IF (col(j) GE 0) AND (row(j) GE 0) AND $ ;only stars within the 256*256
						;image are differenced
	   (col(j) LE 255) AND (row(j) LE 255) THEN BEGIN
		nbhd=img(MAX([0,col(j)-6]):MIN([255,col(j)+6]),$ ;neighborhood
			MAX([0,row(j)-6]):MIN([255,row(j)+6])); around each pt.
				;does not go past the(0,0),(256,256) boundary.
		snbhd=SIZE(nbhd)
		md = MEDIAN(nbhd)
		mnbhd=(nbhd-REPLICATE(md,snbhd(1),snbhd(2)))>0;nbhd with its
						;median subtracted
		ai=REBIN(BINDGEN(snbhd(1)),snbhd(1),snbhd(2));matrix, with the
			size of nbhd, of increasing collumn nos. 
		aj=REBIN(TRANSPOSE(BINDGEN(snbhd(2))),snbhd(1),snbhd(2))
				;transpose of ai		

		mx=TOTAL(ai*mnbhd)/TOTAL(mnbhd) ;row and col #'s of the weighted
		my=TOTAL(aj*mnbhd)/TOTAL(mnbhd) ;centre of nbhd, depending on DN
		bmx=BYTE(mx+0.5) ;rounded byte forms of mx & my
		bmy=BYTE(my+0.5)
		mn = mean(nbhd)
		little=nbhd(MAX([bmx-2,0]):MIN([bmx+2,snbhd(1)-1]),$
			MAX([bmy-2,0]):MIN([bmy+2,snbhd(2)-1]))
		stardn=TOTAL(little); total DN of pixels around (mx,my)
		diff(j)=stardn-md*N_ELEMENTS(little) ;difference between DN
				of star and median neighborhood.
		tot(j)=stardn
		meandiff(j)=stardn-mn; diff. between total DN and mean of nbhd
		;print,nbhd,form='(13I6)'
		;print,little,FORM='(5I6)'
		IF j EQ 0 then print,md,mx,my,diff(j)
		;if diff(j) LT 0 THEN STOP
		stop
	ENDIF ELSE diff(j) = 0

ENDFOR
RETURN
END