Figure 4: Error in estimating the displacement 
of
a particle location from the digitizing grid as a function of
the size w of the mask used for centroid refinement.
Heavy lines are quadrature sums of the error estimates in
eqns. (12) and (13).
Circles are Monte-Carlo calculations for Gaussian surfaces of
revolution with additive noise 
and
halfwidths s = 6 pixels (a) and s = 2 pixels (b).
In both cases, the error estimate provides an adequate
value for both the optimal kernel support, w, and for the
accuracy of the position estimate at that value.