The Ultra Key effect

What you learned: Select pixels of a particular color range to define areas of an image that will be transparent or opaque

Replacing a green screen

Subjects are often filmed in front of a green screen to make it easier to select the background color and make it transparent. That’s why a key is often called a “green screen” effect. Use the Ultra Key effect to make a green screen background transparent.

1. Edit a green screen clip onto V2 in the Timeline, above a clip on V1.
2. From the Effects panel, in the Keying category, drag the Ultra Key effect onto the green screen clip on V2.
3. With the green screen clip still selected in the Timeline, and the playhead over it, open the Effect Controls panel to adjust the Ultra Key effect settings.
4. Click the Key Color eyedropper, and then select the green color in the image displayed in the Program Monitor. Right away, you see the image from V1 where the green had been.
5. If your composite image still has a green cast, in the Effect Controls panel switch the Ultra Key Setting menu to Aggressive, expanding the selected color range to eliminate more green pixels.

Refining the key

The Ultra Key effect can be used to set any color in an image to become transparent and offers additional controls to refine the result.

Use the Output menu to view the Composite Image, the Alpha Channel, or the Color Channel for the applied Ultra Key effect.

Use the Setting menu to expand or contract the selected color range for transparency:

• Aggressive: Expands the pixel color range for added transparency.
• Relaxed: Contracts the pixel color range for reduced transparency.
• Custom: Manually adjust transparency controls.

Additional transparency controls

Matte Generation controls help refine transparent areas:

• Transparency: Adjusts transparency of the source image when keyed over a background. 100 is fully transparent, and 0 is fully opaque. 
• Highlight: Adjusts opacity of the light areas in the source image.
• Shadow: Adjusts opacity of the dark areas of the source image.
• Tolerance: Adjusts the range of colors selected.
• Pedestal: Filters out noise from the alpha channel and can improve the key when working with low light footage.

Matte Cleanup controls help reduce the size or soften the edges of transparent areas:

• Choke: Shrinks the size of the alpha channel matte.
• Soften: Blurs the edge of the alpha channel matte. 

Spill Suppression controls help to clean up green screen keys around light colors, such as blonde hair:

• Desaturate: Removes color from pixels already almost fully transparent.
• Range: Controls the amount of spilled color that is corrected.

Color Correction controls help smooth the color range selected for the key:

• Saturation: Controls the saturation of the foreground source.
• Hue: Controls the hue.
• Luminance: Controls the luminance of the foreground source.

Tip: Command-drag (macOS) or Control-drag (Windows) the eyedropper across the color you want to make transparent in the Program Monitor. This measures a 5 x 5 pixel average of the selected color and usually provides better keying results.