Green Screen Techniques

In this tutorial, I will show you how to key out a greenscreen using the basic tools in After Effects 6.5 Standard.

One thing I want to stress before I even open After Effects is to set up your shot properly! This will save you a HUGE amount of time in post. Here are a couple of tips.

1. Lighting is crucial. At the very least you will need a light to light the greenscreen, and one to light the subject. I did this tutorial with 3 lights -- a Key light (main light on me), a backlight (sometimes called a "rim light"), and a diffuse light to attempt an even light on the greenscreen to avoid harsh shadows. It also helps not to have any creases or lines in your greenscreen. You can find many tutorials online for setting up 3-point lighting.

2. If you do have a wrinkled or otherwise marked up greenscreen, it can help to shorten the depth of field. An example of a shortened depth of field would be to hold your finger in front of your face and focus on it. Notice how everything in the background becomes blurry. To achieve this with your Digital Video camera, either zoom out and get really close to your subject (helps to have a wide angle lens), or get far from your subject and zoom in. Set your camera to manual focus. This will help defocus your greenscreen.

3. Separate your subject from the greenscreen. If at all possible, you should have about 10 feet between your subject and your greenscreen. This will cut out shadows on the screen, and also minimize "bleed" on your subject. Don't worry squeamish people, this only means the green color shows up on the subject.

Alright, enough of the technical jibber-jabber. Let's get on with it! Oh, and bonus tip #4, don't wear small stripes as I did...

STEP 1:

Import your captured video into After Effects, and place it on the timeline.

STEP 2:

If your subject is fairly static, or if you have other things in the shot such as light poles or wires, you can create a garbage matte around the subject using the Pen Tool. This can be a very loose outline. Be sure to leave enough space to choose the key color. For the rest of this tutorial, however, I will not use the garbage matte.

STEP 3:

Select Effects>Keying>Color Range. This will allow us to get the sneaky uneven green pixels. (Try using Color Key if you like, but it is much harder to get good looking results.) Set the Fuzziness to 20 (you can always adjust this). Set the Color Space to Lab. Next to the preview window you will see three eyedroppers. Choose the top one (no "+" or "-" symbol). This will allow you to get a baseline color to key out.

STEP 4:

Find a relatively even green area. You can see that in my example, the right side of my green screen is a bit more even then the left side. Click with the eyedropper to select the green.

STEP 5:

Well that didn't do much on mine, so now I need to increase the range of green included in my matte. Now select the eyedropper with the "+" symbol and choose another fairly even portion of green. Now we're getting somewhere. Repeat step 4 until you can get the background gone. Don't worry about the small bit of green around the subject, we will take care of that next.

STEP 6:

Now to get rid of the green halo. Select Effect>Adjust>Hue/Saturation. Select Greens from the Channel Control. This will focus our adjustments just on the greens in the image. Notice in the channel range there are some triangle shapes above the green part. Move the Green Saturation slider all the way to -100. Adjust the Green Lightness slider to blend the grey with the subject.

If you still see hints of green on the outline of your subject, you can adjust the rectangles in the Color Range by sliding them towards the triangles. This will widen the range of greens being affected.

STEP 7:

Import a background movie or image to test your new-found keying prowess! Depending on your background, you may have to adjust the Lightness slider to blend with your background.

Happy Keying!

Brandon has won several awards specifically for his instructional design work. With a BS in Advertising & Mass Communications and a M.Ed in Instructional Technology, Brandon has been a presenter at educational conferences, and has also taught classes on Photoshop, Dreamweaver, and other new media. He also enjoys playing paintball and scuba diving, although not both at the same time.

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