with a synthetic
  image which has an intensity profile as shown.  The bumps have
  heights equal to 32, 64, 96, 128 and 160. As we increase
  <code>&Delta;</code>, fewer and fewer regions are detected until
  finally at <code>&Delta;=160</code> there is no region
  <code>R</code> which is stable at <code>R(+&Delta;)</code>.
</span>
</div>
</div>

<p>The stability of an extremal region <code>R</code> is the inverse
of the relative area variation of the region <code>R</code> when the
intensity level is incre