Using the Linear Keyer

The Linear Keyer gives you a fast and easy way to composite a front layer on top of a back layer. It is most suitable for keying out backgrounds shot in front of relatively uniform blue or green screens (chroma key).

The Linear Keyer is also useful for pulling simple keys based on luminance values (luma key), such as compositing red letters over a black background.

The Linear Keyer Controls panel includes the following elements.

Output

Outputs the front layer, the generated matte layer, or the composite. Select Matte from the Output list if you want to render a separate matte from the front layer.

Tolerance

Specifies the range of colors that are keyed out (made transparent). Increase tolerance to remove colors further away from the key color. For blue- or green-screen work, you typically adjust this slider until the key color fringe is removed from the image.

Cleanup

Hardens soft edges and semi-transparent regions in the key.

Spill Removal

Adjusts the amount of the key color that is removed from the main portions of the footage. In many cases, a subject shot on blue or green screen contains some color spill of the background onto the foreground subject. Use this slider to color-correct the foreground, removing color shades similar to the key color.

Key Color

Specifies the color to key out. You can specify the key color in two ways: click the color box and select a color in the Pick Color dialog, or click the Pick button, and then click a color in the viewport.

To pull a chroma key using the Linear Keyer:

1. Place a front layer (shot in front of a green or blue screen) over a back layer, then select the front layer.
2. Choose Operators | Keying | Linear Keyer.

The Linear Keyer Controls panel appears.

3. Enable Feedback.

Note: It is easy to attain good results when Feedback is enabled. This lets you see the way the key changes on-the-fly as you change Keyer parameters. If you do not use the Feedback option, you can see the effects of the key in a thumbnail preview to the right of the Linear Keyer controls.



4. Click the color picker , then click anywhere in the solid background color.
5. Increase the Tolerance value until the background color disappears. A value around 20-25% often produces good results.

Warning: When the Tolerance value passes a certain level, you may be keying out portions of the image you want to keep.

6. You can remove more of the unwanted background color from the matte using the Cleanup slider. For basic keys without transparency or finer edge detail such as hair, usually a Cleanup value of 100% works best.
7. After you finish adjusting the Keyer controls, the key color is removed and the back layer appears.

To pull a luma key using the Linear Keyer:

1. Place a front layer (such as brightly colored text in front of a black background) over a back layer, then select the front layer.
2. Choose Operators | Keying | Linear Keyer.

The Linear Keyer Controls panel appears.

3. Click the Key Color box.

The Pick Color dialog appears.

4. Select Black (R=0, G=0, B=0), then click OK.

If the background was uniformly black, you should not need to adjust any values.

Warning: If you set the tolerance too high, the text changes color.

The luma key is complete.