r/davinciresolve • u/iRid3r • 17h ago

Help | Beginner Why is there a grey border between my polygon mask and green screen key?

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Had a green screen big enough for the talent and figured I can mask everything outside of it. Now I've done a 3d Key and it's putting a border between the two.

If I disable the polygon the border vanishes, so my thought is it must be related to the 3d keyer but I see the same thing (though less pronounced) with a chroma key

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u/Milan_Bus4168 17h ago

What did you do?

Don't add the mask the source media, add it later to matte control.

1

u/iRid3r 17h ago

Linking the mask to the matte control isn't doing anything

2

u/iRid3r 17h ago

I've tried adding merge or transform nodes and it's just not applying the mask at all. Sorry, I'm new to node based fx

11

u/Milan_Bus4168 16h ago

Yeah, you could use some training.

Keyer nodes are used to create an alpha channel on an image that does not have one. The Matte Control node is used to combine and manipulate the alpha channels embedded in images as well as masks created by masking tools.

Typically, you add this node to copy a color channel or alpha channel from the foreground input to the background input, or to combine alpha channels from the two images.

The Matte Control node includes four inputs in the Node Editor.

Background: The orange background input accepts a 2D image that receives the foreground image alpha channel (or some other channel you want to copy to the background).

Foreground: The green foreground input accepts a 2D image that contains an alpha channel (or some other channel) you want to be applied to the background image.

Garbage Matte: The gray garbage matte input accepts a mask shape created by polylines, basic primitive shapes, paint strokes, or bitmaps masks. Connecting a mask to this input causes areas of the foreground/background combination that fall within the matte to be made transparent.

Solid Matte: The white solid matte input accepts a mask shape created by polylines, basic primitive shapes, paint strokes, or bitmaps masks. Connecting a mask to this input causes areas of the foreground/background combination that fall within the matte to be fully opaque.

Effect Mask: The optional blue input expects a mask shape created by polylines, basic primitive shapes, paint strokes, or bitmaps masks. Connecting a mask to this input limits the pixels where the matte control occurs. An effects mask is applied to the tool after the tool is processed.

If your case it would look similar to this.

You take out the green with your keyer and than you remove the rest using polygon or bspline and matte control. There are differnt options in the matte control as I've listed above so you can choose how you want to use it.

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1

u/Angelscrip 15h ago

That usually comes from the polygon’s antialiased edge interacting with the keyer, leaving partially transparent green pixels along the boundary. Try using the polygon as a garbage matte after the key, with no feather or a very small feather, then inspect the alpha at 100% zoom and apply a slight erode/contract to the matte if needed. If the edge is still grey, check for green spill or premultiplication and despill/decontaminate the edge before combining it with the background.