title: opencv handling arrow keys with waitKey() function
body: <p>I want to handling arrow keys. but when I print out the input value for waitKey() function, It's 0.
  I don't know why.
  I try to change from "int" to "char" , but It doesn't work.
  How can I solve this problem.</p>
  
  <pre><code>int pos = 100;
  imshow("image", image);
  onChange(pos, (void *)&amp;image);
  createTrackbar("threshold", "image", &amp;pos, 255, onChange, (void*)&amp;image);
  while (1) {
      int Key = waitKey();
      cout &lt;&lt; Key &lt;&lt; endl;
      if (Key == 27) break;
      if (Key == 2490368) {
          pos--;
          onChange(pos, (void *)&amp;image);
      }
      if(Key == 2621440){
          pos++;
          onChange(pos, (void *)&amp;image);
      }
      if (pos &lt; 0 || pos &gt; 255) pos = 0;
  }
  </code></pre>