;       NAME:
;               linBkgdByCol.Pro
;
;       PURPOSE:
;		Returns a background image where the background for each column is calculated from
;		two regions extracted around a trace.
;
;	DESCRIPTION:
;		Given a 2-D spectrum, it calculates a linear background for each column from a 
;		fit of the median of two background boxes.
;
;       CALLING SEQUENCE:
;               linBkgdByCol, pctr, offset1, offset2, image, bkgd
;
;       INPUTS:
;       pctr    - The center of the Pluto trace.
;       offset1 - The lower bound of the background box in pixels away from pctr.
;       offset2 - The upper bound of the background box in pixels away from pctr.
;       image   - The A-B image
;
;       OUTPUTS:
;		bkgd  	- the resulting background image
;
;       REVISON HISTORY:
;       28-APR-2004, CBO, SwRI
;-

pro	linBkgdByCol, pctr, offset1, offset2, image, outarr

; This procedure will extract two boxes equidistant from pctr.  Using the mean coordinate
;	of the columns in the box and the median value of the pixels, a line is fit.  The
;	line is the background for that column.  Caution, do not apply this background far from 
;	pctr.

x1 = mean([pctr-offset2,pctr-offset1])
x2 = mean([pctr+offset1,pctr+offset2])

sz = size(image, /DIM)

p = findgen(sz[1])

outarr = fltarr(sz[0], sz[1])

for i=0, sz[0]-1 do begin

	y1 = median(image[i, pctr-offset2:pctr-offset1])
	y2 = median(image[i, pctr+offset1:pctr+offset2])

	slope = (y2 - y1)/(x2 - x1)
	intcpt = y1 - slope*x1

	bkgd = slope*p + intcpt

	outarr[i,*] = bkgd

end

end

pro linBkgdByColDRIVE

	file =  '/Users/colkin/Work04/Pluto_3um/Reduction/fileNameMaxRow2'
    
    readcol, file, list1, list2, maxrow, format="A, A, F"
    
    num = n_elements(list1)
    
    offset1 = 15
    offset2 = 25
     
;    dir1 = '/Users/colkin/Work04/Pluto_3um/Background3/'
    dir2 = '/Users/colkin/Work04/Pluto_3um/BackgroundSubt3/'
	datadir = '/Users/colkin/Work04/Pluto_3um/Rectified6/'
    dirAonly = '/Users/colkin/Work04/Pluto_3um/BackgroundAonly2/'

	for i=0, num-1 do begin

		d1 = readfits(datadir+list1[i])
		d2 = readfits(datadir+list2[i])
		
		linBkgdByCol, maxrow[i], offset1, offset2, d1-d2, outarr
		
;		writefits, dir1+list1[i], outarr
		writefits, dir2+list1[i], d1-d2 - outarr

; need the background signal for each image to calculate the variance maps
;	which are needed for the optimal extraction.

		linBkgdByCol, maxrow[i], offset1, offset2, d1, outarr
		writefits, dirAonly+list1[i], outarr
		
	endfor
	
end

pro linBkgdByColDRIVETriton

	dir = "/Users/colkin/Work04/Triton_NIRSPEC/"
	
	file =  dir+"Reduction/filePairs"
    
    readcol, file, list1, list2, maxrow, format="A, A, F"
    
    num = n_elements(list1)
    
    offset1 = 15
    offset2 = 25
     
    dir2 = dir+'BackgroundSubt/'
	datadir = dir+'Rectified1/'
    dirAonly = dir+'BackgroundAonly/'

	for i=0, num-1 do begin

		d1 = readfits(datadir+list1[i])
		d2 = readfits(datadir+list2[i])
		
		linBkgdByCol, maxrow[i], offset1, offset2, d1-d2, outarr
		
		writefits, dir2+list1[i], d1-d2 - outarr

; need the background signal for each image to calculate the variance maps
;	which are needed for the optimal extraction.

		linBkgdByCol, maxrow[i], offset1, offset2, d1, outarr
		writefits, dirAonly+list1[i], outarr
		
	endfor
	
end