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This is part two of my articles covering the basics of green screen and chroma key. If you missed part one, which covered general green screen knowledge, check it out here.
This article will strive to answer the question: How do you use a green screen and chroma key properly?
Here are the most important things to consider when using a green screen for a shoot: 1) First of all, lighting is paramount. Diffused, even lighting is needed on the screen. 2) Your subject should be lit separately from the green screen. 3) Your subject should be positioned at such a distance from the screen so that he/she does not cast shadows or create light spills onto the green screen. 4) Your camera should be set with proper color balance and exposure settings. 5) Finally, in post-production, use Chroma Key to pull out the green and replace it with whatever you want.
Without further ado, let’s break it down step by step in more detail below! Make sure to watch some of the videos along the way, which makes for some good supplemental show and tell.
How To Light A Green Screen
The correct lighting setup will save you or your editor a large headache in post-production when dealing with green screen footage. What must be understood is that two lighting setups are needed to get the desired result.
The first setup should focus entirely on lighting your green screen.
The goal here is to light the entire screen as evenly as possible with no outsized pockets of brightness or shadow.
Consistency is the name of the game, which is usually the opposite of traditional set lighting designed to evoke moodiness or contrast, and therefore is an easy mistake for first-time green screen shooters to make.
Use Soft And Diffused Lighting For The Green Screen Background
To evenly light a green screen, soft light is a must. Pointing an uncovered light at a green screen will create harsh falloff and unevenly expose your background, making it near-impossible for your editor to pull a clean key.
To make the light soft, you need to use diffusion. Diffusion is just a fancy term for silk or other semi-transparent sheets of material used to soften the light. All you have to do to diffuse the harshness of direct light is place the diffusion in front of it, covering the light.
The easiest method is to purchase a kit of softbox lights. They come equipped with silks that attach easily to the boxy frame of the light. While intended for photography, these work very well for green screen lighting.
If your budget is tight, DIY always works. Grab any thin white sheet you’ve got, or even a plain white t-shirt, and affix it to the lights you have. Be careful how hot your lights get, you don’t want to burn your diffusion!
For a basic lighting setup, a minimum of two lights should be enough to cover your green screen evenly.
Place them a few feet back from the screen (out of the shot, of course) and at about a 45-degree angle.
This placement, plus diffusion on your lights should make your screen camera ready!
It can be tricky to figure out exactly where in relation to the green screen your subject should be placed once the background is ready.
A general rule of thumb is, the further back you are from the screen, the cleaner the key.
A good range to place your subject is around ten feet from the screen.
If your space is tight, five or six feet could work, too, but any closer and you’re risking a messy key that will spread to your subject.
If you’re unsure about placement or can’t measure it, then further back is better.
The reason for this is simple: the more distance, the harder it is for color spill from the green screen to fall onto your subject. Also, when your subject is at a good distance from the screen, shadows from your subject won’t fall onto the green screen.
When you achieve the perfect distance, then ideally there will be no spill onto the subject from the screen and no shadows on the screen cast by the subject.
This is what we mean by a clean key—the separation of the subject (foreground) and screen (background) so that the chroma key software recognizes the distinction and keys out only the desired portion of the frame.
The color temperature of the lights you use to light the green screen is also important.
It is recommended to use a color temperature of 3200K a.k.a. tungsten which should give you a nice balanced image where the green is neither too blue nor too orange.
If you want to learn more about lighting and color temperatures, we recommend you read our Video Lighting Guide Part 1: Different Types of Light.
Once your subject is in place, then theoretically you can light them how you wish, since their distance from the screen should protect the screen itself from any shadows thrown by the subject.
We don’t all have ideal studio setups, however, so you may need to fiddle around and make sure your subject’s lights are not impacting the screen behind them in any way.
Generally, the classic three-point lighting setup should work fine, or, if you don’t have space for a backlight, then a simple two-point key and fill setup on your subject.
Once your lights are set up for both subject and screen, you’re nearly ready to shoot! Let’s get onto the last thing we need to check, which is…
You’ve done a lot of hard work setting the lights up just right for shooting, so it would be a shame to invalidate it all with an incorrectly calibrated camera.
Here are three things to check to make sure your camera is properly set for your green screen shoot:
- Exposure – Make sure the image is properly exposed and that the screen actually registers as green in-camera. If the image is too dark, or too blown out, then you won’t get a clean key.
- Resolution – Keep the resolution as high as you can. The more detail recorded, the easier it will be to key accurately.
- Color Temperature – Make sure the white balance of the camera is set correctly for the lights you are using. As I wrote earlier, I recommend you use tungsten light with a color temperature of 3200K, which gives you a nice balanced image where the green is neither too blue nor too orange. So make sure to set your white balance to 3200K as well.
And that’s it from a production standpoint. Once your footage is shot, ingested, organized, and ready to edit, then comes step two:
Chroma Key – Premiere Pro
There are many editing platforms out there that offer this functionality, but I’m going to cover Premiere Pro because it’s the most ubiquitous now, having replaced FCP 7 some five to six years ago.
Premiere Pro has a great battery of tools for editing green screen footage in the Keying folder under the Effects tab. There are two choices: the basic Color Key and the Ultra Key. While similar in functionality, I will cover Ultra Key thanks to more fine-tuning options.
- Once your green screen footage is in the timeline, drag the Ultra Key effect onto it.
- In the Effects tab, use the eyedropper icon to select the green background to be keyed out.
- In the Setting dropdown, fiddle around with each choice to see which setting is best for a clean, total green key—relaxed, aggressive or default.
- If your image is noisy, all is not lost. The Matte Generation object can help. It can be adjusted to help key out any pesky highlights or shadows that are still stubbornly clinging to your image. Play with the settings to see what gets you the best look.
- For working your edges like a meticulous barber, use the Matte Cleanup option. You can shrink the edges of the key with the Choke feature, and you can fuzz them up with Soften (similar to Feathering in Photoshop).
- Spill Suppression can help fix the edge colors if your subject still appears slightly green-tinged despite your best efforts. You have four settings to play with to fix any color spill: Desaturate, Range, Spill, and Luma.
- The Color Correction tab can help to saturate or pop your colors more if your lighting setup or camera wasn’t correctly set during shooting. This is your last chance to help get a clean key by differentiating the colors.
- Finally, with your key set, grab the clip or image replacing the green, and drop it into the timeline under the keyed footage. This will leave the unkeyed footage visible while showing the replacement footage in the “empty” space that was keyed out. Think of it like laying a partially filled-in overhead slide over another one. The bottom one shows through in the empty spaces of the top.
If, after tweaking all the settings above, you’re still not getting a key you’re satisfied with, then some emergency fixes might be simply cropping, resizing, and reframing your shot.
Remember when we said to shoot at the highest resolution possible? If you did, then you’ll have some leeway to crop and zoom without noticeable quality loss. This can help you clear out pesky parts of the frame that (hopefully) aren’t too close to your subject.
Get Comfortable With It!
And you’ve done it. These are the basics of shooting and keying green screen video. You may run into some issues the first time you do it, but take it as a learning experience and remember, each successive time will be that much better.
Once you’re comfortable shooting and keying green screen, you’ll develop tricks and shortcuts of your own. When that happens, feel free to come back and let us know what tips you’ve gained from your experiences!
If you liked this article or have something to add, toss us a comment below and let us know.
About the author
Nikola Stojković is a writer and filmmaker based out of Chicago. His short films have screened at festivals across the USA. When not shooting, he enjoys writing film reviews and playing his accordion, Fortunata.