Keying out backgrounds using a green or blue screen in After Effects becomes much simpler once you know the core settings of Keylight, the built-in keying plugin.
The number of settings the plugin offers can be daunting at first. But once you get to know exactly how they function, the process becomes a lot simpler.
Let's jump in and get to grips with Keylight, so you can get the most out of keying your footage.
The Process Starts in the Camera
Before we get started, it's important to note that even with all the tweaking of minutiae in Keylight's settings, if the footage you're working with isn't properly shot, the results will vary.
As a rule, ensure that your subject is separated as much as possible from your background. Also, make sure that your shot is evenly lit and that the color of your subject's clothes doesn't match the background (wearing a green top with a green screen is a huge mistake).
Try and avoid shadows behind your subject with your lighting setup (these are harder to remove in Keylight). Any wrinkles or deformities in the green screen behind the subject show up after keying, so get that ironed out if you're using a fabric background!
If you're comfortable with advanced camera settings, ensure you're using a high shutter speed to remove motion blur. Also, employ a higher f-stop to better blur the green background behind your subject, and bring them into focus.
Once you're happy with your footage, it's time to start keying.
Applying the Keylight Plugin
If you don't have any footage on hand to practice with, there is a variety of royalty-free stock footage available online to download. For this tutorial, we used a stock video of a subject behind a green screen from Pexels.
This footage is well-shot, and hits on all the points we mentioned earlier—it's evenly lit, shows no visible shadows, and has a good distinction between the subject and background. This makes the process of keying much smoother.
Once you've imported your selected clips into After Effects and created a new composition, it's time to add the Keylight plugin. As with any effect, it can be found in the Effects & Presets panel, under the Keying subfolder.
Just click and drag the effect onto your footage to apply it. In the Effect Controls panel, you'll be able to adjust the various settings and parameters.
Keying Your Footage
When first applying the effect, nothing happens. This is because the color to key has not yet been selected. A color can be chosen by using the Eyedropper tool in the Screen Color setting.
The color to select is the background color you want to remove, which would be the green background behind the subject. Click that with the Eyedropper tool and it should vanish.
The initial result looks promising—the edges appear quite well-defined and the green has vanished. However, under a black backdrop, it's easier to miss artifacts and shadows left by the green screen.
To get a better view of the quality of the key before adding a background, try viewing your keyed footage over a white shape layer. This better highlights anything critical that needs to be removed.
On white, it's still a decent result, though some of the edges appear a little softer and discolored from the green screen. This is where you can use Keylight's sliders to try and create a cleaner outcome.
Adjusting the Settings in Keylight
Playing around with the parameters and settings within Keylight can let you adjust how the image is keyed, and iron out issues. Let's run through these now.
- Screen Color: As already covered, this creates the matte using the main color of the background.
- Despill Bias: This allows you to try and offset "spill," where the background has reflected (or "spilled") onto the subject. This can be particularly prevalent in skin tones and around the edges of hair.
- Alpha Bias: Can be used to try and offset issues from color imbalances when unlinked from the Despill Bias.
- Screen Gain: Controls how much of the screen color is removed. A higher value keys more of your color.
- Screen Balance: This tries to offset issues occurring from unevenly lit background screens.
- Screen Pre-Blur: Can help smooth over any errors or issues with the edges of keyed footage. It also adjusts how much blur is applied to the matte.
- Clip White and Clip Black: Adjusting the Clip White can help reduce issues of transparent and see-through subjects. The Clip Black works almost in reverse, reducing the issue of subject and foreground artifacts appearing in the background.
- Clip Rollback: If your edges appear to be lost or over-keyed, this setting can help try and recover them.
- Screen Shrink/Grow: Adjusts the size of your mask and edges.
- Screen Despot Black/White: This allows you to try and remove spots that can sometimes appear while keying footage.
- Foreground/Edge Color Correction: This allows you to adjust the hue, saturation, and color of your keyed subject.
Putting Keylight in Practice
Now you know the settings within Keylight, let's adjust the key to get a sharper result. Earlier, it was identified that the edge of the keyed subject had retained some edge softness from the green screen, which was particularly visible around the shirt.
To fix these, the Screen Shrink setting can be employed to remove this residue. However, the adjustment does not need to be significant—adjust it too much and you cut into your subject. To avoid this, let's set it to -2.
This now seems a lot cleaner. When the keyed footage is in motion, the blurred edges are no longer visible.
Now, let's try placing him somewhere new. In this example, we'll put him outside of a market stall.
The result is that the edges are clean, but it's still obviously a keyed image. Now, it's time to apply color correction and brightness adjustment to get the subject to look more like he's part of the background.
You may also want to adjust the key settings slightly, as the edges now feel a little too sharp. This can be achieved by adjusting the Screen Pre-Blur setting.
Here is the finished result. A lens flare has been added to create a shared sense of light, and a blur has been applied to the backdrop to make it feel more like a natural background image seen through a camera.
Level Up Your Video Editing Skills
This was an introductory article to the settings and features in the Adobe Keylight plugin to treat pre-shot footage. Once you get the hang of it, your subjects will blend right in to whatever background you plan on placing them on.
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