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How to Key Greenscreen Video in Adobe After Effects

There are several ways to get the job done when it comes to chromakeying or greenscreen. One of the most popular ways (in fact its even used on feature films and broadcast television) is Adobe After Effects. Pros turn to After Effects for the best results when keying. While there are several powerful tools that allow for accurate mask creation and refinement, there’s one workhorse in the bunch that does nearly all of the work… Keylight.

Keying in Adobe After Effects

To get the job done in After Effects, we’re going to turn to a built-in recipe for keying. There’s a great combination of filters to use and its already set up as a preset.

Step 1: Add your footage and your background to one composition.

Both the greensscreen footage and the background used in the video are courtesy Adobe Stock

Step 2: Place the background you want to use below the video track and adjust its duration to match your footage.

Step 3: In the Effects & Presets panel, type the word Keying.

Step 4: Drag the preset called Keylight + Key Cleaner + Advanced Spill Suppressor, not the top track (the greenscreen footage).

Now it’s time to follow the recipe and complete the key.

Tip: If you need backgrounds for greenscreen (both realistic and graphical) be sure to check out Adobe Stock for a huge selection.  You can even search right inside After Effects in the Libraries panel.

The Initial Key with Keylight

The technology used in Keylight uses a core algorithm written by the Computer Film Company.  The technology has been used in numerous feature films including Harry Potter, Mission Impossible, and Sweeney Todd. Keylight has won the Academy Award for Technical Excellence. The Keylight plug-in can be a bit intimidating since it has nearly 60 parameters.  The good news is that there are only a few main controls while the rest are just used for fine-tuning. Let’s start with some basic material that needs to be keyed.

Step 1: In the timeline, click on the greenscreen track so it is selected.

Step 2: Locate the Effect Controls Viewer.

Step 3: Move the Current Time Indicator to the start of the composition by pressing the home key. You are now ready to start the keying process.

Step 4: Click the eyedropper next to Screen Colour to activate the selection eyedropper.

Step 5: 
Click just over the shoulder of the subject. You want to click close to the person to remove the green areas closest to the subject.

Footage courtesy Adobe Stock

On first glance, the key looks perfect.  It’s not, as close examination will reveal that the image has extra transparency and some spill that needs to be corrected.

Step 6: In the Effects panel, click the drop-down menu next to View and switch to Screen Matte.  This lets you see the grayscale matte that Keylight uses to create transparency.

Step 7: Examine the matte closely. The matte indicates transparent areas in black, opaque areas with white, and partially transparent areas with gray.

Step 7: Increase the Screen Gain parameter to push the background towards a clean black plate. Some users alternately will use the Clip Black slider discussed below for similar results.

Step 9: Change the Screen Pre-blur to a value of 1.0 to slightly soften the edges of the generated matte. Avoid using a high value or halos will occur.

Cleaning Up the Matte

For a believable key, it’s good to have some gray pixels around the edge of the subject (so hairs and other semi-transparent elements can blend into the background). The background, however, should be solid black and the foreground should be solid white. Currently, the background is in pretty good shape but the foreground can really use some work.

Step 1: Click the disclosure triangle next to Screen Matte to reveal several controls that can be used to fix matte problems.

You can use the following sliders to refine the mask.

  • Clip Black: This makes the blacks in the matte darker
  • Clip White: This makes the white areas in the matte whiter.  Be careful with both clip controls to not overdo it and ruin the edges of your foreground.
  • Clip Rollback: This allows you to undo clipping and bring the edges back.
  • Screen Shrink/Grow: This control can contract or expand the matte.
  • Screen Softness: This softens the generated matte.
  • Screen Despot White: This parameter removes white specks that are inside a generally black background.
  • Screen Despot Black: This parameter removes black specks that are inside a generally white foreground.

Tip: Gently Scrub Your Keys
When adjusting properties in Keylight, you need a gentle hand.  Go even the littlest too far and you’ll have poor results.  When using sliders, try holding down the Command key to scrub any property value in tiny, subtle increments

Step 2: Switch the results back to Intermediate Result to hand off the keying to the next two effects.
DO NOT PICK FINAL RESULT or you won’t get the desired effect.

Cleaning Up the Key

Now things get pretty easy as the next two effects are mostly automatic. These clean up the edges and remove any leftover color spill. If your subject stands too close to the background unwanted green may reflect in their skin or clothes.

Step 1: Click the fx icon next to the Key Cleaner effect name in the Effect Controls panel to see how this affects the key.

Step 2: In the Key Cleaner controls, check the box for Reduce Chatter to get even smoother results.

Step 3: Finally, turn on the Advanced Spill Suppressor effect by clicking the fx icon next to its name.
This effect is off by default as you don’t want to remove the green until after you’ve completed the key.

Step 4: Set the Composition quality to Full to get an accurate preview.

Step 5: Press the spacebar to load a preview and see how the effect plays back. After the files are cached, it will preview in real-time.

Step 6: If you are finished, you can choose Composition > Add to Render Queue.
Choose the settings you need and export your final video. Be sure to see the built-in help menu for more on rendering movies.

Greenscreen and background videos are from Adobe Stock

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