I often use paint.net to alter the backgrounds of photos. I use the paint bucket function. (Yes, I am a super newbie - amatuer, etc). Many times if I am trying to alter the background to a solid white with an object that is also light colored the paint bucket function colors much of the object white as well. I understand how to adjust the tolerance and sometimes can overcome the problem. I have tried to use a background color that is more of a contrast to a light or white object (ex. grey), but the same thing tends to happen. I had reasoned that if the background is an obvious contrast paint bucket would only alter the contrasting color.
My question is what is how paint bucket tool function - how does it decide what to alter to white for example? Is there any way to overcome this with background colors?