Improving Your Greenscreen Shooting and Keying in Adobe After Effects

Part 1 - setting up and shooting properly using a greenscreen

A portrait of David Lynn of England as he planks on a bin in front of a television greenscreen ahead of the BMW PGA Championship at Wentworth on May 21, 2013 in Virginia Water, England. Warren Little/Getty Images

Keying and compositing is the act of removing and replacing portions of a shot to put together something new. In production or at home, most of the time, this means keying out a green or blue screen and placing the subject - usually a person - over top of a new background.

Like most things in video, there are easy ways to jump right in and learn to greenscreen with ok results, and there are ways to go beyond the basics and do a better job.

In this article we’ll cover tips for using the built in effects in Adobe After Effects, but keep in mind that good greenscreen jobs start at the shoot, and anybody who has had to “fix it in post” knows that less fixing is best.

When shooting there are many considerations. First of all, put some distance between the subject and the greenscreen to help keep light from bouncing from the screen onto the subject, creating spill. Doing this serves a dual purpose - it also allows room for lights behind the subject and minimizes how harsh the subject’s shadows appear on the screen behind them.

Next, the screen should be a green non-reflective material (cotton, muslin cotton, matte paint, etc.), and it should be evenly lit, with the subject and screen lit separately. It doesn’t have to be green, but digital cameras work best with green screens over other colors. Bright or “hot” spots where light is brighter in one area of the screen than other areas may not key properly, so try to keep it even.

To avoid shadows from wrinkles and creases in a soft screen, clamp the screen thoroughly to the stands holding it up. Most large box home builder stores should carry inexpensive clamps that will do the trick.

When choosing cameras, there are determining factors (compression, etc.), but let’s keep it simple.

Keep everything looking sharp and avoid any chance of out of focus shooting by decreasing the aperture of the camera to bring about infinite - or near infinite - focus. E.g. set the aperture to f/22 versus f2.8.

Additionally, when shooting moving subjects with a camera like a DSLR motion blur can become an issue. To compensate, try compensating by increasing the camera shutter speed. Try 1/80 of a second or better to minimize blur, as it’ll be difficult to remove green from blurred footage. Also try to keep ISO set as low as possible, as higher ISO settings introduce noise into the shot. More noise means a more crumbly, tougher keying job.

There are plenty more best practices, but most will be learned on the set. It’s time for us to import the footage into After Effects and get keying.

In part two of this series we'll get into some best practices for bringing the footage into Adobe After Effects and removing the green from a shot and replacing it with a different background.

This will serve as the basis for a longer plan to improve green screen skills over the coming weeks. Once we can effectively use After Effects to create cool composited shots, we will take the time to learn how to sweeten our shot to make it more realistic.