title: Android: loading an alpha mask bitmap
body: <p>I have a single-channel PNG file I'd like to use as an alpha mask for Porter-Duff drawing operations.  If I load it without any options, the resulting Bitmap has an RGB_565 config, i.e. treated as grayscale.  If I set the preferred config to ALPHA_8, it loads it as a grayscale ARGB_8888 instead.</p>
  
  <p>How can I convince Android to treat this file as an alpha mask instead of a grayscale image?</p>
  
  <pre><code>mask1 = BitmapFactory.decodeStream(pngStream);
  // mask1.getConfig() is now RGB_565
  
  BitmapFactory.Options maskOpts = new BitmapFactory.Options();
  maskOpts.inPreferredConfig = Bitmap.Config.ALPHA_8;
  mask2 = BitmapFactory.decodeStream(pngStream, null, maskOpts);
  // mask2.getConfig() is now ARGB_8888 (the alpha channel is fully opaque)
  </code></pre>