title: Ignore certain area(roi) in an image while processing in Matlab
body: <p>I'm a fresher to Matlab. I'm working on
  vision.CascadeObjectDetector on Mat-lab and is used
  twice to find-out two different objects(separately
  trained), say E and K from a video. bbox and bbox2
  are respective ROIs. part of code in while loop is given below:</p>
  
  <pre><code>videoFrame=step(videoFileReader);
  bbox=step(letterDetector_E,videoFrame);
  bbox2=step(letterDetector_K,videoFrame);
  C = vertcat(bbox,bbox2);
  videoOut=insertObjectAnnotation(videoFrame, 'rectangle', C, 'E&amp;K');
  step(videoPlayer, videoOut);
  </code></pre>
  
  <p>I want to ignore the area denoted by bbox while finding out bbox2. That is, no two object should be find out from same part of image(obviously there are similiarities in both type of objects). So I wish to mask or ignore bbox area of videoFrame while 
  bbox2 is assigned with step(letterDetector_K, videoFrame)
  is executing. Format of bbox is [xUpperLeft, yUpperLeft, width,
  height]. 
  How can I do that.</p>