FUNCTION sharpness,ima,d
;
; Evaluation of image sharpness according to the SST algorithm
; (see Thesis by Luc Rouppe van der Voort)
; but independent on window size.
; INPUT: image array - IMA
;	 shift in pixels - D (4 pix recommended)
; CALLING: sharpness_value = SHARPNESS(ima,4)
;
; 24 September 2003, Michal

on_error,1
si=size(ima)
if si(0) ne 2 then message,'  Not a 2D image'
xn=si(1)-1
yn=si(2)-1
ave=total(ima)		; =(avg_int*n_pixels), independent
; ----------------------------------------------------------
; ave=total(ima)/si(4)	;average intensity, used at the SST
; ----------------------------------------------------------
sx=total(abs(ima(d:xn,*)-ima(0:xn-d,*)))
sy=total(abs(ima(*,d:yn)-ima(*,0:yn-d)))

RETURN, (sx+sy)/ave
END