The “Chroma Key” is one of the most often used visual effects in the film industry. The Chroma Key is an effect most commonly know to key out a green or blue screen. However there are also several other uses for the Chroma Key in postproduction. Lets go over a few of them:
This technique is widely used in broadcasting especially for weather reports, and for business videos. However it is rare to find a straight on Chroma keyed shot where just the background is replaced in a featured film. Think on YouTube, where there are multiple video of a host talking to the audience standing in front of a green screened background. This is the most basic use for keying and is what many people thing is the limitation.
Now imagine a FreddieW or FinalCutKing video, they use green screens in a much more complex manner.
When keying out a green screen you are making an invisible background for the subjects in the shot. After keying out the green, you can still use all the transform tools you want on the clip. Position it wherever you want on the background, and change the size to make tiny people or giant people.
If you want to make ghosts or spirits in your video, chroma keying is the way to do it. Once the green is keyed out you can alter the transparency of the clip and add other filters like color correction and glow. You can also animate your ghost using keyframes. Perfect for Ghostbusters or Lugi’s Mansion parodies
Add Scenery or other Elements:
Anything can be shot in front of a green or blue screen and be put into a video. Plants and building can be shot, keyed, and then composited into a scene to add effect or create a scene that is in an imaginary place.
Many explosions, bullet shots, or in this case watermelons… are shot in front of a green/blue screen and then composited into action videos. In this case Final Cut King threw a watermelon sliced in half to composite over a clip of him swinging a knife (which was also chroma keyed) to make it look like he is chopping the watermelon in mid-air.
The most important thing about chroma keying is the set up and shooting not the editing! Properly lighting a green screen could make or break your video. A Green screen WILL NOT be chroma keyed successfully if it is not lit right.
The main aim to shooting in front of a green screen is eliminating shadows. If you have shadows on your screen when recoding, After Effects will recognize those shadows as BLACK not green. Therefore they will not be keyed out and you’ll end up like this…
Many people will tell you that you need a kit of studio lights to properly light a green screen. But if you can’t afford these lights (like me) there is a much easier, (and better in my opinion) method to shooting your green screen shot. Set up your green screen outside, or in a room with a lot of windows. When I’m at home, I shoot my green screen shots in my sunroom. You will get the best result on an overcast day
1. Daylight will be light up your shot for you, and
2. Because the sun isn’t out you won’t have to deal with any shadows. This especially works well if the shot you are composting the shot for an outside scene.
If you don’t have access to a sunroom, or you just rather prefer shooting studio style then you will need to carefully set up your lighting. You don’t have to necessarily go out and get those expensive light kits (even though they work the best). What ever lighting you use you just want to sure that every part of your green/blue screen that’s in frame is illuminated and the subject is illuminated.
Again what we are looking for is for as little shadow as possible and for a consistent color of green on the green screen (or blue on a blue screen). Also take care of your green screen don’t let it get many wrinkles in it because that ruins the consistency of the color on the screen.
Chroma Keying in After Effects
Chroma Keying can be done in almost every editing and motion graphics software (even iMovie). But it is most effect if After Effects. In a Chroma key effect there are two layers in the timeline. The top one is your Chroma keyed clip and the bottom is the desired backdrop.
This works because the Chroma keyed clip will have a transparent background therefore showing the layer under it, which will be the desired backdrop. The effect you use is called “Keylight”.
Put this effect on your green screen clip then use the dropper to select a region on-screen. Don’t be alarmed if your entire green screen isn’t gone.
You can adjust the “screen gain” and “screen balance” to get rid of some more green. Also under the “Screen Matte” drop down there are some more options you can use to get rid of all the green. One thing I suggest is first putting you Chroma keyed clip on top of a white solid so you can clearly see every green spot. Don’t do it on top of the black background because it is hard to pick out some of the darker specs of green.
Play the clip all the way through because sometimes green spots appear here and there. If there is a section of green that does not go away and it does not interfere with your subject, you can always just mask that part away with an inverted mask.
Also don’t worry about any lights or maybe any bare walls on the sides of your screen. As long as your subject does not pass over them you can mask them out as well.
Once you are done with keying and masking. Put in your background layer and see how it looks. Adjust your subject layer so until you have your desired effect.
A way to make the scene look more believable is to add color correction to your subject to match the color tones of your background. Also assuming you shot you clips on a tripod (which you should with Chroma keying), you can also add a bit of camera shake in after effects by using the wiggle tool, or by downloading a camera shake plug-in like the free one on VFX Bro’s website.
Chroma Keying is tough! Don’t expect to get it perfect on your first try. My first try at is was completely awful. But when you do something wrong, you always find something you can do better. If you are going to Chroma key for something little like a school project or for your family, don’t worry about spending a lot of money to make it look perfect, because will have no idea if you did anything wrong. But if you are looking to become big on YouTube or in the business, you need to learn how to Chroma key correctly from start to finish because when you’re in the professional industry and you present a clip with green spots everywhere, you’re going to probably lose your job, or if you are on YouTube, people will dislike your video and you will lose subscribers. It really is the one area in visual effects where if it is not perfect, it can ruin a shot in a movie. But again if you’re just doing it for fun and for practice, don’t worry about making mistakes.
Green screens can be found on many video production websites online. Tubetape.net is a popular one for entry-level green screens and other equipment.
Each week I will touch upon a different technique used in VFX, most of them of After Effects. These include, masking, cloning, motion tracking, title sequences, lens flares, color correction, and much more!
If you want to see some of the projects I have made my Channel on YouTube is CKproductions1000. We release a new video every other Friday!