;+
; NAME :	current
; PURPOSE :
;	calculate the electric current distribution based on 
;	vector magnetograms of the Solar Flare Telescope
; CATEGORY :
; 	lib/flare
; CALLING SEQUENCE :
;	jz = current(bx,by,bin=bin)
; INPUTS :
;	bx,by	-- transversal mag. field in Gauss*10
; OPTIONAL INPUT PARAMETERS : 
;	none
; KEYWORD PARAMETERS :
;	bin	-- binning factor
; OUTPUTS :
; COMMON BLOCKS : 	none
; SIDE EFFECTS :
; RESTRICTIONS :
; PROCEDURE :
;
; MODIFICATION HISTORY :
;	K.Ichimoto	'93/07/18
;-
function current,bx,by,bin=bin

if not keyword_set(bin) then bin=1
s=size(bx)	&	nx=s(1)	&ny=s(2)
jz = convol(rebin(bx,nx/bin,ny/bin),[[-1,-4,-1],[0,0,0],[1,4,1]],12)  $
        +convol(rebin(by,nx/bin,ny/bin),[[1,0,-1],[4,0,-4],[1,0,-1]],12)
return,jz
end