Greenscreen Shooting in Adobe After Effects: Part 2

It's time to fix that greenscreen footage in post!

Green Screen area at AT&T and Samsung's presenation of Keith Urban's Get Closer 2011 World Tour at Mississippi Coast Coliseum on June 16, 2011 in Biloxi, Mississippi. (Photo by Erika Goldring/Getty Images for AT&T & Samsung)
Green Screen area at AT&T and Samsung's presenation of Keith Urban's Get Closer 2011 World Tour at Mississippi Coast Coliseum on June 16, 2011 in Biloxi, Mississippi. Photo by Erika Goldring/Getty Images for AT&T & Samsung

In part one of this series we took a look at some basics for setting up and capturing greenscreen footage for the purpose of keying and compositing, or removing and replacing a background to our newly shot foreground.

To accomplish the act of compositing we will be using Adobe After Effects, and in particular, a keying effect called “Keylight”. It was created by The Foundry, and ships as a built-in effect with After Effects.

It is a powerful tool, and, while most of us will have our own tips and tricks, here are a few of our favorite techniques.

It should be noted that there are plenty of keying options aside from this one, including powerful tools in Premiere, HitFilm and other applications, but this is a good way to put out some fundamentals in keying.

To start, let’s set up Keylight properly. The beginning of this tutorial is to do the first step with any keying effect: apply the effect to the footage, and choose the screen color with the color picker. This is one of the first options in the effect panel for Keylight, and the color that needs choosing is the green background.

Just picking the green background with Keylight’s color picker (or “colour” picker, as UK company The Foundry spells it) will do half the job. The background should be mostly transparent now, but there’s more we can do.

Keylight settings - of the many settings exist in Keylight we’ll just look at a few:

1) Screen Pre-blur: this setting adjust how much blur to apply to the matte before the key is pulled. This is handy for removing any bizarre imperfections in the footage edges. After choosing the screen color, this is generally the first place to go.

2) Screen Matte view: by working in this view to adjust the screen matte, it’s easy to see what our matte is looking like. There’s nothing worse than having a shadow from a not-totally-gone screen. Adjust Clip Black and Clip White until the subject is white and the screen area is black. If there is a line around the edge of the subject, feel free to roll back the screen with Screen Shrink. Start with -0.5 and work from there. Return to Intermediate or Final Result to finish.

There are plenty more settings, but these will get you started.

What else can we do to improve our key in After Effects?

Use a Garbage Matte - in any keying situation, it’s good practice to create a garbage mask, which is a mask surrounding the subject to remove as much excess background as possible. This removes any darker edges, and generally saves the keyed the effort required to key out the entire screen.

Using a Track Matte to Fix Ugly Keys - once Keylight has been applied and set on the layer needing to be keyed, duplicate the later. On the bottom layer, remove the Keylight effect. On the bottom layer, set the track matte to “Alpha Matte” using the top layer as the track matte. That will use the matte created by Keylight, but the clean non-keyed footage is what is seen as a final result. Pre-compose the two layers so they can be affected as one layer.

Continue to work on the pre-comped layer using things like a matte choker to clean up the edges, spill suppressor to get rid of any green spill, or use hue/saturation to desaturate green areas of the clip.

In part three of this series we'll look at color adjustments and other changes that can make a composited image more realistic.