title: Edit only alpha layer in GIMP
body: <p>I'm trying to create a "corona" effect (like the sun's corona) in an image using GIMP, but I'm having trouble editing only the alpha channel of the image.</p>
  
  <p>I want the RGB to be pure white (255, 255, 255) and the alpha layer to have a brush effect applied to it. I know how to use the brush, but no matter what combination of masks or layer visibility / channel visibility settings I try, it will never edit ONLY the alpha channel, leaving the rest undisturbed.</p>
  
  <p>How can I edit only the alpha channel of an image in GIMP?</p>