title: How to change the background color of a saved transparent bitmap
body: <p>I am opening a png image into a Bitmap, making some modifications to it and then saving it to disk as a jpg.  In the case where the png has some transparent areas, they are saved as black.  Is there a way to change this default behavior so the image is saved with a  different color background such as white? </p>
  
  <p>Thanks</p>