By the way, what do you think of my idea to stuff the added flux value into the image as a member.  So you would just write `im = obj.draw(dx=0.3)`, and the added flux would be stored as `im.added_flux` (or `im.flux_added` -- I'm not sure which is better).  I checked that this would work.  You can just add the item to the im object and it accepts it just fine, even thought he im is a wrapped C++ object.  

I think this syntax is a bit nicer.  And it wouldn't be backwards incompatible for draw commands (although it would be for drawShoot commands), so it wouldn't break as much existing code.