If you’ve ever keyed out a green screen and ended up with your actor looking like they just stepped out of a toxic waste barrel — yeah, I’ve been there too.

That’s also a great way to make the audience go, “Oh... that’s fake.” Which is also a great way to make your client or supervisor go, “Hey, you’re fired.”

So let’s fix that.

If you want your composites to look realistic, getting a clean key is non-negotiable. In this tutorial, we’ll walk through 5 key tips (pun unfortunately intended) for better chroma key results — using After Effects and Keylight as our tool of choice.

Use a Properly Lit Green Screen

Before you even touch your software, the most important factor in getting a clean key is how your footage was shot.

First rule: make sure your green screen is evenly lit. No shadows, no bright spots, no weird gradients creeping across the background. Just a clean, flat green. Uneven lighting is one of the biggest causes of fringing and artifacts during keying.

Next, think about distance. The closer your subject is to the screen, the more green spill is going to bounce onto them. By giving your subject more space from the background, you cut down on that glow before it even starts — and your keyer will have a much easier time.

Bonus: Need some properly shot green screen footage to practice with? We've got a free Practice Footage Library. It has several green screen shots to help you practicing keying and compositing.

When to Use a Blue Screen Instead of a Green Screen

In most cases, green screens are the go-to. They tend to key out cleanly in daylight scenes and play nice with natural lighting.

But there are times when blue makes more sense:

• If your actor is wearing green, obviously.
• If you’re shooting a nighttime or low-light scene — blue screens retain shadows better and preserve more detail in dark areas.

So if green’s giving you trouble, it might not be your fault. Switch colors when it makes sense.

How to Use Keylight in After Effects

Once you’ve got solid footage, it’s time to key — and if you’re in After Effects, Keylight is your friend. It’s powerful, free, and built right in.

Here's a quick breakdown:

• Screen Colour: Use the eyedropper to select your background.
• Screen Gain: Controls how aggressive the key is. Higher = more background removal (and more danger to your subject).
• Screen Balance: Helps fix uneven lighting by adjusting the color channels.
• Clip Black / Clip White: Fine-tune the matte edges. Clip Black removes leftover junk; Clip White locks in the solids.
• Screen Matte View: Flip to this mode to see your alpha channel. It’ll show you what’s really being keyed — which is super helpful for fixing trouble spots.

Take your time here. Zoom in. Toggle between modes. This is where “meh” keys become production-ready.

Kill the Spill

Even with solid footage and a clean matte, green spill happens — especially around hair, fabric edges, or shiny surfaces.

• Keylight has built-in spill suppression controls. Use them.
• Tweak these after your matte is dialed in.
• Desaturate or rebalance the edges to neutral tones.
• Watch out for skin tones — don’t trade green glow for zombie skin.

Garbage Mattes: Not Glamorous, But Super Useful

Garbage mattes help your keyer focus only on the subject. That means:

• Faster rendering
• Less chance of noise and edge errorsFinal Polish: Matte Cleanup & Edge Refinement Once your key is mostly working, flip back to Screen Matte View and check your edges.

Final Polish: Matte Cleanup & Edge Refinement

Once your key is mostly working, flip back to Screen Matte View and check your edges.

• Use Clip Black/White to tighten things up.
• Look for semi-transparent fuzz or inconsistent edges — especially in hair or fine detail.
• You want clean, solid separation. No gray halos. No crunchy outlines.

This last step takes time, but it’s the difference between “that’s obviously keyed” and “wait... that’s composited?”

Practice Green Screen Keying

Want to practice? Download a few clips from the Practice Footage Library (500+ professionally-shot practice clips for compositors) and give it a try!

If you're unfamiliar with ActionVFX, we house the world's #1 trusted library of professional-grade VFX stock footage (things like fog, debris, explosions, fire, and more).

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