Chroma Key After Effects
Chroma key is another term for what is commonly called green screening. It is when you shoot a subject in front of a green or blue screen and replace all the green or blue in frame with another image or video. Adobe After Effects is a video editing program that does numerous motion and video effects, including chroma key. Many consider After Effects one of the best programs for doing chroma key because of the many specific capabilities the program has.
The Green Screen
It is important when setting up your green screen that you get the fabric as wrinkle-free as possible. The most effective technique is to use a steam iron. Make sure it is hung evenly and that there are no unnecessary folds. Wrinkles and folds can cause distracting shadows in post production. Also make sure no part of the subject is green, including clothing and props. If there's a similar color, it might display the background image instead of the subject. This is why most green screens have a blue side. Also when you place the subject in front of the green screen, make sure there is enough separation so you can light the subject and the green screen separately. Getting the shot right originally makes post production a lot easier.
After Effects
After Effects is a giant software. It can be frightening to try and do anything, let alone something as technical as chroma key. You cannot let the scope of after effects scare you though. It is a huge program with a billion little things that will help you with any video project, but the thing to remember is that all the little things are fairly simple. Check online for tutorials for after effects like the ones linked to below. They are not difficult to find, and they can teach you a lot of neat tricks or general knowledge about the program.
Keylight
One of my favorite ways to do chroma key with After Effects is with a plug in called keylight. Keylight comes with all new versions of after effects, but if you have an older version you can download keylight for free. The reason keylight is such a great plug-in is because it is so easy to use. It makes it possible to do advanced green screening edits easily and quickly. To use keylight, all you have to do is select the color you want to remove with the eyedropper, and then it replace that color with black.
Shadows
Keylight also has a simple way to remove the excess green from your subject. Obviously the better the job you do when shooting the video the easier your edits will be. However, any minor problems can usually be easily fixed with keylight and after effects. Once you have selected the color you want removed from the image change the view to "Screen Matte." This will give you a black and white version of the image. Everything being removed will be in black and everything remaining will be in white, so it is very easy to see any overlap. Then adjust contrast and the colors in the screen matte view until the gray areas disappear. If there are any specific green reflections in your subject they can easily be selected and deleted.
Outline
One of the most common problems with using a green screen is the outline on the subject image. No matter how great the actual shot is set up there is almost always this pesky halo like outline. This is from the point on screen where the light from the subject and the light from the green screen blend. Keylight also has a handy setting that helps you get rid of this. Depending on the size of the outline you can enter a value into the screen shrink and grow setting. If you enter a negative number it will cause the subject image to shrink. If you set the value low enough then this will get rid of just your outline. I suggest starting with -3 and then tweaking from there.
Tags: After Effects, after effects, green screen, After Effects, Chroma After