title: Compare intensity pixel value Vec3b in OpenCV
body: <p>I have a 3 channel <code>Mat</code> image, type is <code>CV_8UC3</code>.
  I want to compare, in a loop, the intensity value of a pixel with its neighbours and then set <code>0</code> or <code>1</code> if the neighbour is greater or not. 
  I can get the intensity calling <code>Img.at&lt;Vec3b&gt;(x,y)</code>. </p>
  
  <p>But my question is: how can I compare two <code>Vec3b</code>? </p>
  
  <p>Should I compare pixels value for every channel (BGR or <code>Vec3b[0]</code>, <code>Vec3b[1]</code> and <code>Vec3b[2]</code>), and then merge the three channels results into a single <code>Mat</code> object?</p>