pro even_light_pedestal, adu_in_fov, back_pix_raw, sloped=sloped,	$
	gain, P1pP2, P1, P2, P1pP2sigma, P1sigma, P2sigma, valid_img=valid_img

;+
; NAME:
;	even_light_pedestal
; PURPOSE:
;	
; CATEGORY:
;	camera/idl/cert
; CALLING SEQUENCE:
; INPUTS:
; OPTIONAL INPUT PARAMETERS:
; OUTPUTS:
; OPTIONAL OUTPUT PARAMETERS:
; INCLUDE:
	@compile_opt.pro		; On error, return to caller
; CALLS:
;	InitVar, gridgen, LocalExtrema
; PROCEDURE:
; MODIFICATION HISTORY:
;	???-200?, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
;-

InitVar, sloped, /key

nimg   = n_elements(adu_in_fov)
nvalid = n_elements(valid_img)

if nvalid eq 0 then	valid_img = indgen(nimg)

; Calculate gain by making mean intensity in fov the same for all images

gain  = adu_in_fov/mean(adu_in_fov[valid_img])

dgain = gain[valid_img]-1
dback = back_pix_raw[valid_img]

; Calculate P1+P2 and P2 by linear fit between gain-1 and background

jj = linfit(dgain, dback, sigma=sigma)
P1pP2 = jj[0]
P2    = jj[1]


;================

if sloped then begin
	zmin   = min(dback-(P1pP2+dgain*P2), max=zmax)
	nslope = 100
	slope  = 5*(zmax-zmin)/(nimg-1)*gridgen(nslope,range=[-1,1])

	chisq = fltarr(nslope)
	for i=0,nslope-1 do begin
		jj = linfit(dgain, dback-slope[i]*valid_img, chisq=zval)
		chisq[i] = zval
	endfor

	slope = interpolate(slope, LocalExtrema(chisq, /minima, /float))

endif else	$
	slope = 0.


;========================


if slope ne 0 then begin
	jj = linfit(dgain, dback-slope*valid_img, sigma=sigma)
	P1pP2 = jj[0]
	P2    = jj[1]
endif

P1pP2 = P1pP2 + slope*findgen(nimg)
P2    = P2    + fltarr(nimg)
P1pP2sigma = sigma[0] + fltarr(nimg)
P2sigma    = sigma[1] + fltarr(nimg)

P1 = P1pP2-P2
P1sigma = sqrt( P1pP2sigma*P1pP2sigma+P2sigma*P2sigma )

return  &  end