e open MATLAB and load a test image</p>

<div class="highlight"><pre><span class="n">pfx</span> <span class="p">=</span> <span class="n">fullfile</span><span class="p">(</span><span class="n">vl_root</span><span class="p">,</span><span class="s">&#39;data&#39;</span><span class="p">,</span><span class="s">&#39;spots.jpg&#39;</span><span class="p">)</span> <span class="p">;</span>
<span class="n">I</span> <span class="p">=</span> <span class="n">imread</span><span class="p">(</span><span class="n">pfx</span>