title: Any one tell me why we write this 0xff000000 in filters?
body: <p>Here is my code for GrayScale filter want to know about this</p>
  
  <pre><code>class GrayScale extends RGBImageFilter {
    @Override
      public int filterRGB(int x, int y, int rgb) {
      int a = rgb &amp; 0xff000000;
      int r = (rgb &gt;&gt; 16) &amp; 0xff;
      int g = (rgb &gt;&gt; 8) &amp; 0xff;
      int b = rgb &amp; 0xff;
      rgb = (r * 77 + g * 151 + b * 28) &gt;&gt; 8; 
      return a | (rgb &lt;&lt; 16) | (rgb &lt;&lt; 8) | rgb;
      }
  }
  </code></pre>