How to Use Chroma-Key on Adobe After Effects

By Anthony Oster

Updated September 28, 2017

Items you will need

  • Digital video camera

  • Blue or green screen

  • Adobe After Effects

Chroma-key, also known as blue or green screen imaging, has been a mainstay of Hollywood special effects since the 1930s. First utilized by Linwood Dunn, chroma-key imaging utilizes the luminance level of blue or green colors and replaces everything at a higher luminance level with a new layer of film. This technique allows films to depict superheroes flying, epic battles in outer space and dinosaurs roaming around downtown Los Angeles. Adobe After Effects is a post-production program bundled with the Adobe creative suite and gives usres the capability to create chroma-key effects at home.

Film a sequence to be chroma-keyed.

Purchase a blue or green screen large enough to cover the area of the scene that is to be chroma-keyed.

Light the screen uniformly and pull it taut to remove any wrinkles. Wrinkles and poorly lit areas of the screen will result in a poor chroma-keyed image in post-production.

Film the scene in a high-quality filming format to produce a more realistic chroma-key transfer in post-production.

Save the scene to your computer for use in post-production.

Using Adobe After Effects to chroma-key your film.

Click the pen tool at the top of the program and click the “RotoBezier” option to create a garbage matte around the subject being keyed. A garbage matte should consist just of the area immediately surrounding the object(s) being keyed. With the pen tool, click the areas around your subject to complete the garbage matte.

Open Adobe After Effects. Choose the video file to be chroma-keyed. Click “effect” then “keying” and finally choose the “keylight” option in After Effects. This will open the keylight effects and controls panel. Click the eyedropper icon under the “Screen Image” section of the keylight effects panel and select an area of the background to be keyed out. Try to keep this close to your subject.

Click the drop down menu under “View” on the keylight effects panel and choose the “Status” option. The black areas are portions of the video that will be keyed out, the white areas are the elements of the subject that will remain in the shot. Grey areas are areas that will be transparent in the final film. Click and hold the number under “Screen Gain” and increase it gradually until the grey areas disappear. The “Clip White” menu will increase the strength of the white areas, or the opaqueness of the white ares.

Import the footage that you want to utilize in the keyed area by clicking “File” then “Import.” Drag the file from the project menu to the timeline and place it below the clip that you chroma-keyed in the previous steps.

Export the file by clicking “composition” and “make movie.”

Tips

Check the garbage matte, screen gain and clip white levels at different points on the timeline of the clip.

Warnings

Objects and clothing that is within the color range of the chroma-keyed color will also be removed from the clip as well.

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