title: transform single channel of BitmapData object
body: <p>I have a BitmapData object with an alpha channel. I'd like to know the fastet way to offset that alpha channel in ActionScript3 (FlashPlayer10). By offsetting I mean shifting all pixels of that channel in one direction (wrapping around the image borders) while leaving the color channels as they were.</p>
  
  <p>Is there a good way to apply a such a transform to one channel only? </p>