How to Chroma Key in After Effects

What You’ll Need

Adobe After Effects (any recent version)
A video clip with a green or blue screen background
A replacement background image or video (optional)

Step-by-Step

Import your footage – Go to File > Import > File (or drag and drop) to bring your green screen clip and background into the Project panel.
Create a new composition – Drag your green screen clip onto the New Composition icon at the bottom of the Project panel, or right-click and choose New Comp from Selection.
Apply Keylight – With your clip selected in the timeline, go to Effect > Keying > Keylight (1.2). This is the standard chroma key effect in After Effects.
Pick the screen color – In the Effect Controls panel, click the eyedropper next to Screen Colour and click on the green (or blue) area of your footage in the Composition panel. The background should turn black immediately.
Refine the key – Adjust the Screen Gain and Screen Balance sliders to improve the transparency. Increase Screen Gain to make the background more transparent, and adjust Screen Balance if there’s a color cast.
Clean up edges – Under Keylight’s Matte Generation section, increase Clip Black and Clip White slightly to tighten the matte. Use Screen Shrink/Grow to remove any fringe.
Add your background – Drag your replacement background into the timeline below your green screen clip. It will show through the transparent areas.
Fine-tune with spill suppression – Under Keylight’s Spill Suppression, use the eyedropper to select the screen color again. This removes green or blue reflections on your subject.

Common Mistakes

Uneven lighting – Shadows or bright spots on the green screen make keying difficult. Ensure the screen is lit evenly.
Using a color that matches the subject – If your subject wears green, the key will remove parts of them. Use a blue screen instead.
Over-adjusting settings – Crankingsliders to extremes can make the subject look jagged or hollow. Make small changes.
Forgetting to check the alpha channel – Always view the alpha channel (click the Alpha toggle in the Composition panel) to see if the matte is clean.

Tips

Shoot with the highest quality possible – compressed footage (like from phones) is harder to key.
Use a dedicated green screen kit or paint that is specifically designed for chroma keying.
Position your subject at least a few feet away from the screen to minimize spill.
If Keylight isn’t perfect, try adding a garbage matte (mask) around your subject to remove unwanted areas.
Use the Key Cleaner and Advanced Spill Suppressor effects (Effect > Keying) for more complex footage.

Troubleshooting

The background isn’t fully transparent – Increase Screen Gain, or adjust Clip Black and Clip White. If the screen has shadows, use the Screen Matte settings to fine-tune.
Edges are jagged or have halos – Use Screen Shrink/Grow to shrink the matte slightly, and increase Clip White to reduce halos. Also check the Spill Suppression.
The subject has holes (transparent spots) – This happens when the subject’s clothing matches the screen color. Try lowering Screen Gain, or use a different screen color.
Keylight isn’t available – If you’re using an older version, you might need to use the Color Key effect instead, but Keylight is included in all standard versions.
The background flickers – This is often due to motion blur or compression. Try increasing the Screen Gain slightly, or use the Despill Blue/Green settings.

Frequently Asked Questions

Can I chroma key with a blue screen instead of green?

Yes, blue screens work just as well. Use the eyedropper to select the blue color in Keylight. Blue is better if your subject has green elements.

Do I need a professional green screen?

No, a smooth, evenly lit green wall or fabric works. Avoid wrinkles and shadows.

How do I remove green spill from hair?

Use the Spill Suppression in Keylight, or add the Advanced Spill Suppressor effect. You can also manually adjust the color with a Hue/Saturation effect.

Can I key out a moving background?

Keylight works best on static screens. If the background moves, you may need to track the screen color or use a different keying method.

Why is my keyed footage pixelated?

This is usually due to low-resolution footage or heavy compression. Try shooting in a higher resolution and use a higher bitrate.

What if my subject has a green tint?

Use the Spill Suppression and also try the Color Balance effect to correct the tint.

Sources: Adobe Support. Menus and buttons can differ slightly by version. Spotted something out of date? Tell us.