class="o">|</span><span class="n">R</span><span class="o">|</span>
</pre></div>


<p>where <code/>|R|</code> denotes the area of the extremal region
<code/>R</code>, <code/>R(+&Delta;)</code> is the extremal region
<code/>+&Delta;</code> levels up which contains <code/>R</code> and
<code/>|R(+&Delta;) - R|</code> is the area difference of the two
regions. </p>

<p>A stable region has a small variation. The algorithm finds regions which
are &quot;maximally stable&quot;, meaning that they have a lower variati