function plot_norm_curve(avg, std,option,ylim)

xx = [0:255];
yy = exp(-(xx-avg).^2/(2*std*std));
yy = yy/ (sum(sum(yy)));
hpl = plot(xx,yy,option);
ppl = get(hpl,'Parent');
set(ppl,'YLim',[0 ylim]);
set(ppl,'Xlim',[0 250]);
plot([0 250 250 0 0], [0 0 ylim ylim 0]);
return;
 
