imread (repost)

[Przemek Klosowski]

   > 
   > But what does 'not visible' mean? Should we just show the background  
   > color of the figure?
   ...
   > If so, I can easily imagine myself being confused  
   > whenever I see an all gray image -- am I looking at an all gray image  
   > or a transparent one?

   Depends on the contents of the background and on the contents of the alpha channel.  A gray background (as opposed to white or black) and potentially single shaded images isn't a good combination in any circumstance.

GIMP (after Photoshop I think) has a special 'working surface
background' pattern, a light-dark gray 5mm checkerboard, that is
understood to show up if the manipulated image layers are transparent.