title: How to make pixels with a certain RGB range transparent
body: <p>I have a fixed size <code>frame buffer</code> (1200x720 RGBA efficiently converted from YUV) in a java byte array. </p>
  
  <p>I would like to set a certain shade of a color (white in my case, regardless of its alpha value) to fully transparent. </p>
  
  <p>Currently I am doing this via CPU by traversing the byte array and zero'ing the pixel if <code>RGB &gt; 0xC8</code>. This somewhat works but is obviously extremely slow (>1sec/frame) for doing so on a live stream. </p>
  
  <p>I've been researching methods to do this via <code>GPU/OpenGL</code> on Android and I see mentioning of Alpha test, blending, and color keying. It seems the alpha test is not useful here since it relies on the alpha information rather than RGB's values.</p>
  
  <p>Any idea how to do this on Android using OpenGL/java?</p>