title: Why use Blur for Smoothing the image?
body: <p>I am new to OpenCV. I am going through O'Reilly Learning OpenCV.
  Book tells about using Blur (Low pass filter), dilation and erosion(Opening Morphological operator) to remove noise.</p>
  
  <p>but before processing image for Opening morphological operator(i.e Erosion followed by dilation). he always does Blur ?</p>
  
  <p>Why do we need to blur image before processing even when Erosion followed by dilation remove noise ?</p>