title: Binarization and Background Filtering in opencv
body: <p>Shortly, I want to make the pre-processing procedures before OCR with the suggestion comes from <a href="http://www.abbyy-developers.eu/en:tech:insideocr:adaptive_binarisation" rel="noreferrer">ABBYY 's technology</a>. There are two parts in article:</p>
  <ul>
  <li><strong>Background Filtering</strong>: separate text strings from background.
  <img src="https://i.stack.imgur.com/vfASf.png" alt="enter image description here" /></li>
  <li><strong>Adaptive Binarization</strong>: make lines and words will be correctly detected and higher recognition accuracy will be reached. And they try to impact on characters.
  <img src="https://i.stack.imgur.com/j8xEA.png" alt="enter image description here" />
  <img src="https://i.stack.imgur.com/GmJKs.png" alt="enter image description here" /></li>
  </ul>
  <p>I wonder are there any ways to achieve them by using <code>opencv</code>? Any suggestions or sample codes would be appreciated.</p>