Chroma Key
Chroma Key removes one colour from a clip, such as a green screen, so whatever is on the tracks behind shows through.
- Where
- Clip tab ▸ Picture ▸ Chroma Key
- Agent tools
set_video
Key out a color
Section titled “Key out a color”-
Put the clip on a track in front of what should show through, and select it.
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In the Clip tab’s Picture sub-tab, open the Chroma Key section. It comes after Corner Radius and is closed by default.
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Choose Pick from Canvas and click the background in the preview. That sets the colour and turns the key on. Or tick Key out a color, which keys pure green.
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Adjust Tolerance, Softness and Spill until the edges look right.
Turning the key on gives pure green at 20 % Tolerance, 10 % Softness and 50 % Spill. Key Color, Tolerance, Softness and Spill stay greyed until the key is on. Pick from Canvas doesn’t. The section’s header reads “off”, or the Tolerance as a percentage. Reset takes the key off the clip.
The section is there for clips of a video file, image clips and freeze frames. Text, shape, graphic, adjustment and nest clips don’t have it. With several clips selected, an edit keys all of them.
Key color
Section titled “Key color”The colour to remove. It starts as pure green, and the swatch takes any colour. The opacity in the colour panel has no effect here, because a key colour has none.
Pick from Canvas
Section titled “Pick from Canvas”Choose Pick from Canvas and the preview reads “Click to pick the key color · Esc to cancel”. One click on the picture sets Key Color. The button works with the key off, and a pick turns it on.
A pick reads the clip as the key sees it, without the clip’s own key, grade and opacity. So picking again reads the same green the first pick did, even though that green is now a hole. A clip in front of it at that point still covers it, and you get what’s visible there.
Picking again changes only the colour. It keeps the Tolerance, Softness and Spill you set.
To cancel, press the button again, press Esc or change the selection.
| If | What happens |
|---|---|
| You click outside the picture | Frame Job beeps and stays ready for another click |
| You click where the canvas holds nothing | Frame Job beeps and changes nothing |
| The selection changes while the frame is being read | Frame Job beeps and changes nothing |
Only one canvas tool is ready at a time. Pick from Canvas ends Obscure’s Place on Canvas, Zoom to Region and the qualifier’s Pick from Canvas.
Tune the key
Section titled “Tune the key”Start with Tolerance to clear the background, then Softness for the edge, then Spill for any fringe of the key colour.
Tolerance
Section titled “Tolerance”How far from the key colour still counts as background. Everything that close is removed completely. Raise it if patches of background remain, and lower it if the key eats into your subject.
The range is 0 to 100 %, and the default is 20 %. The quick picks are 0, 10, 20, 40 and 60.
Softness
Section titled “Softness”How gradual the edge of the key is. Past Tolerance, the picture fades back in over this distance, so a low value gives a hard edge.
The range is 0 to 100 %, and the default is 10 %. The quick picks are 0, 5, 10, 25 and 50.
How much of the key colour is removed from the edges that remain. Pixels in the soft edge are pulled toward a grey of their own brightness, which takes out a green fringe. It works only in that edge, so with Softness at 0 it has almost nothing to act on.
The range is 0 to 100 %, and the default is 50 %. The quick picks are 0, 25, 50, 75 and 100.
Animate the key
Section titled “Animate the key”With an action selected, Key Color, Tolerance, Softness and Spill set the value at the action’s end and animate toward it. The colour blends through the OKLab colour space along the action. Pick from Canvas also sends its colour to the action’s end.
Good to know
Section titled “Good to know”- The key runs before the grade, so grading a clip doesn’t change what’s keyed. A camera log conversion and the source conversion come first, so the key sees the converted picture.
- Show Ungraded leaves the key on.
- How a key behaves when a project switches between SDR and HDR is on A project’s dynamic range.
With an agent
Section titled “With an agent”An agent sets the key with set_video, using the same colour and the same three amounts written as 0 to 1. It has no Pick from Canvas, so it passes the colour as numbers. See Tools: picture and grade.