{
	Calculation of contrast-based scalefactor

		8/17/93

	Input:   ex = picture exposure
	   or:	 Lwa = world adaptation luminance
	Output:  sf = scalefactor for display
		 adj = corresponding exposure adjustment
		
	Optional Inputs: Ldmax = maximum display luminance
			 Lda = display adaptation luminance
}
Lwa = WE*.5/ex;
Ldmax = 120;
Lda = Ldmax/2;

sf = ((1.219 + Lda^.4)/(1.219 + Lwa^.4))^2.5 / Ldmax;

adj = WE*sf/ex;