Re: [Gimp-user] How do I prevent the paint tool from drawing outside of the selection?

[Ofnuts <ofnuts laposte net>]

On 25/08/14 15:43, wizzythegrape wrote:
> I have a picture I'm editing with gimp. I've made a selection of part of this
> picture that I'm trying to paint. When I do this, it effects pixels outside of
> the boundaries of my selection. This is the first time I've seen this. Does
> anyone know how to prevent/solve this?
>
> Thanks.
>
> Attachments:
> * http://www.gimpusers.com/system/attachments/147/original/example.png
The marching ants are not the limit of the selection, they are where the 
selection has a 50% value, so pixels outside the area marked by the ants 
can be partially selected. Each time you paint over them they are 
painted slightly. This isn't noticeable on the first strokes but become 
more visible after several strokes.

For what you want to do, protecting pixels with a selection isn't an 
efficient technique (problems such a the one above, halos, jagged 
edges...). You should be using Color-to-alpha (or paint in Color Erase 
mode) to remove the old color, and apply the new color in "Behind" mode.

Some more explanations here: 
http://gimpforums.com/thread-proper-subject-extraction-background-removal-and-background-painting<http://gimpforums.com/thread-proper-subject-extraction-background-removal-and-background-painting>