Is there a node to expand alpha after painting?

Is there a node that would expand the alpha channel in the areas that I painted in? For example, if I painted an area in RGBA, but I wanted the alpha channel to have a larger area/border.

Hey Katie, I think Matte Repair node under the KEY section might be worth a whirl.
You can shrink and grow the matte just in the alpha of a paint stroke with that one.


@TimH Thank you! Works great, and what I really needed was to fill my paint that had varying opacity values with 100%, and grow the alpha. But, I also need something to work when I have a white alpha, with the painted areas being black.

Hey Katie, if you put an invert node set to Alpha before the matte repair you should have what you need.

@TimH Thank you, yes, I already do that. I have to especially do that when using the Mocha plug-in as after using the Render module the alpha turns white. And then auto paint with obey mask does not work with a white alpha.

Also, one thing to keep in mind is to not switch the Fill type on the Source node after you have started a project as you will get irregular alpha behavior if you paint with alpha one way, then switch the fill to another option, then paint with alpha.

Thank You for that info Katie about the Alpha, might save me some pain.

It’s not a defect for obey mask, it’s just how the roto shapes are passed down through to the paint node. I don’t think obey is technically using shapes as the obey source, but if the shapes are over a solid white alpha then it doesn’t work. I have been thinking about a couple possible alternatives without having to use an invert node, like inverting the roto shape in the object list. I could also be off on some of this and Marco can chime in to advise. :slightly_smiling_face:

If your source has a solid white alpha, adding shapes will just add white to white which is not what you want. In that case, get rid of the alpha in the Source settings. To do this, select the source thumbnail in the Trees window and set the Alpha > Fill parameter to Transparent.

1 Like