title: How to convert grayscale bitmap into alpha mask?
body: <p>I have a grayscale JPG picture, and I'd like to load it into Bitmap of format <code>Bitmap.Config.ALPHA_8</code>. Is that possible, how can I do that?</p>
  
  <p>It's straightforward to load alpha channel from a PNG (which can have empty R,G,B channels), but I'd like to use JPG for compression.</p>
  
  <p>This is a followup question to <a href="https://stackoverflow.com/questions/5098680/how-to-combine-two-opaque-bitmaps-into-one-with-alpha-channel">How to combine two opaque bitmaps into one with alpha channel?</a></p>