Remove a green screen in After Effects

The short answer

To remove a green screen in After Effects, apply a keying effect, usually Keylight, to the footage layer. Sample the green background with its screen colour eyedropper, then refine the resulting matte so the subject stays solid and the background becomes transparent. Most clean results also need spill suppression, which removes green tint reflected onto the subject, and sometimes a mask, called a garbage matte, to cut away parts of the frame the key cannot handle.

There is one important limit. After Effects works on recorded footage after the fact. It does not replace a background live during a video call. If you want a different background in real time on a webcam feed, you need a virtual camera or the background feature in your conferencing app, not an After Effects composition.

What keying does and how it differs from live background replacement

Keying, or chroma keying, makes every pixel close to a chosen colour transparent. A green screen gives the software one even colour to target, so the separation between subject and background comes from colour rather than from guessing where the person is.

Live background replacement in webcam and conferencing software often works differently. Many of those tools use segmentation, where software estimates the outline of a person in each frame, so they can run without a green screen. Some also offer a green screen option. In general, live tools favour speed. Keying in After Effects lets you inspect individual frames, adjust settings over time, and render at full quality. The trade-off is that it only works on footage you have already recorded.

Before you start

• Footage where the green background is lit as evenly as possible. Shadows, wrinkles and hot spots make the key harder.
• A subject who is not wearing green and who stands far enough from the screen to limit green light reflecting onto them.
• A background layer, such as an image, video or solid, to place behind the keyed subject.
• Your After Effects version noted. Effect names and menu locations described here reflect long-standing Creative Cloud releases. No version-specific documentation was supplied for this guide, so check the menus in your installed version.

Step-by-step: keying with Keylight

• 1. Import your green screen clip and create a composition from it, or drag it into an existing composition.
• 2. Place your replacement background on a layer below the green screen layer.
• 3. Select the green screen layer and apply Keylight. In recent versions it is usually found under Effect > Keying > Keylight (1.2), and you can also find it by searching for it in the Effects & Presets panel.
• 4. In the Effect Controls panel, click the Screen Colour eyedropper and select a representative area of green near the subject.
• 5. Change the View setting to Screen Matte. White areas will stay visible, black areas will become transparent, and grey areas will be partly transparent.
• 6. Under the Screen Matte settings, raise Clip Black until the background shows solid black. Lower Clip White until the subject shows solid white. Make small adjustments, because pushing either setting too far eats into hair and edges.
• 7. Use Screen Shrink/Grow and Screen Softness if the edges look too hard, too soft, or show a green outline.
• 8. Switch View back to Final Result and check the subject against your new background.

After Effects also includes an animation preset that combines Keylight with Key Cleaner and Advanced Spill Suppressor. In many versions it appears under Animation Presets in the Effects & Presets panel, in an image utilities category. Applying the preset gives you the main keying and cleanup tools in one step. Its exact location may differ between versions.

Cleaning up the result

• Garbage matte: draw a rough mask around the subject with the Pen or shape tools. This removes light stands, the edges of the screen and other areas outside the green.
• Spill suppression: if the skin or hair edges look green, adjust Keylight's despill settings or add Advanced Spill Suppressor.
• Edge recovery: Key Cleaner can help restore fine detail, such as hair, that a strong key removes.
• Difficult shots: if the screen is badly lit or the subject moves into areas without green behind them, keying alone may not be enough. Roto Brush, which separates a subject by tracking its outline, can supplement or replace the key.

How to check that the key worked

View the Screen Matte again and step through frames where the subject moves quickly, turns, or has hair or loose clothing near the edge. A good matte shows a solid white subject, a solid black background, and grey only where the edge is meant to blend. Then check the final composite against both a bright and a dark background, because faint edge problems often show up on only one of them. Preview the clip at full resolution before rendering, since problems can be hidden at reduced preview quality.

What this means for recorded speech

Keying only changes the image. If your webcam clip includes audio from the webcam's built-in microphone or a separate mic, the audio stays on the same layer and is not affected by Keylight or the cleanup effects. Because the key happens after recording, it cannot improve how the speech was captured. If you plan to record webcam footage for keying, set up and check your microphone before recording, since After Effects will not fix those problems later.

Evidence gaps

No subject-specific evidence was supplied for this guide, so it contains no measured settings, recommended numeric values or version-specific menu paths confirmed against a particular release. The workflow above reflects After Effects' documented, long-standing keying tools, described in general terms. Confirm effect names and menu locations in your installed version, and expect the best settings to vary from shot to shot depending on lighting and footage quality.