Using green screens, also known as chroma keying, allows video producers to virtually layer any image or video in the background while having a subject (actors, props, etc.) in the foreground. Green screen backgrounds (or blue screens depending on the situation) are used in anything from high-budget Hollywood movies to video conferences calls. What makes them useful in all scenarios is their increased flexibility, giving you the ability to essentially add any setting you desire and, most notably, do so in a controlled environment.
To better understand the concept of green screens, here is an example from the “The Matrix.”
The use of green screen backgrounds in this movie is revolutionary, and in this particular scene, the production crew used multiple cameras to render 2D shots into a 3D creation. It is pretty astounding what can be accomplished with green screens. But before we get to “Matrix” status, let’s start by understanding a few essential keys to working with green screens.
Types of green screens
You can use a green fabric that is relatively durable but is prone to wrinkles. Another option is painting a wall with green paint, useful for fixed spaces. You can also use green paper, but although easily shaped into any arrangement, it tends to break easily.
If you are on the go, you can use a portable green screen (some have green on one side and blue on the other) because they are convenient, but they cannot be made larger than what you get. Alternatively, one of the most accessible aspects of greens screens is that you can make one yourself.
The size of green screen backgrounds
Depending on the type of scene or effect you want to accomplish, the size of the green screen is essential. For example, if you are recording a closeup or medium shot to add simple green screen backgrounds, you can get around it using a smaller screen. However, when you want to record a long shot showing your talent from head to feet, you will need a much bigger green screen. It’s this situation that involves a significant part of chroma keying successfully.
The space of your studio
To accomplish a successful chroma keying, your talent must be as far away from the backdrop as possible. If you are recording in a very tight spot, it will make it more challenging to pull this off. If your talent is too close to the screen, it can cause spills from the lights illuminating the talent. In the case of recording a long shot of your talent, you need to be aware that the camera needs to be sufficiently far to get the full shot. At the same time, the talent needs to be far away from the backdrop and positioning lights appropriately for the shot, which brings us to the next thing.
Positioning the lights
Make sure to position lights on the left and right sides of the green screen and at the same distance. Another thing to keep in mind is not to put the light directly at your subject, which can cause shadows.
6 basics do’s and don’t of green screens
1: Talent way too close to green screen
When your talent is too close to certain green screen backgrounds, the green luminance of the screen reflects back onto the subject. You will notice a green spill either surrounding the talent or in some regions of the subject body. To fix this, all you need to do is keep your subject as far away from green screen backgrounds as possible.
2: Not enough light on the green screen
It is essential to light the green screen evenly, making it look like one, uniform green-colored piece. If you light your screen and see some areas darker than the others, it means the screen is not evenly lit. To fix this, do not put the light’s head on to the screen. Instead, put at least two sets of lights on the left and right sides of the screen and at the same distance.
3: Shadows on the green screen
If there are any shadows reflected on the screen, it will make the keying in post-production considerably more challenging. This usually happens when the light of the talent is casting a big, dark shadow. To fix this, make sure to light the subject separate from your green screen while keeping the backdrop evenly lit. Be aware that you can still key successfully in post even with some very light shadows, but do your best to avoid them.
4: Wrinkles in the green screen fabric
If you are using fabrics for green screen backgrounds, make sure they do not have any wrinkles because they will make it very difficult to light the screen evenly. Wrinkles cause uneven surfaces on the screen, which can cast tiny shadows on the green screen.
To fix this, it is recommended that you use string clips holders to keep the screen tight and wrinkle-free. After carefully stretching the screen with strings, use a steamer to remove the remaining wrinkles. Be aware that the steamer should not make your screen wet because if it does, your screen will have a dark, damp area and you will be forced to wait for the screen to dry.
5: Not considering the virtual scene lighting
If you want your end product from green screen to look as realistic as possible, you need to keep in mind the lighting of the virtual scene you will be adding in post. For example, if your scene is at night and you lit your subject like the sun is on top of them, you have a lighting mismatch. To fix this, it will solely depend on your virtual scene, but in general, make sure the green screen is lit evenly and light your talent accordingly without affecting the green screen. In post, make sure to use color correction and color grading to match the scene perfectly.
6: You don’t need to cover the entire frame with green
When shooting with green screen backgrounds, you may think that you need to ensure you cover the entire frame with green because it saves time in post. The issue here is that if you are trying to cover everything in green and notice later that you introduce (by mistake) too much green spill, you are adding extra time to remove the spill in post-production.
The solution is that while shooting, position the camera and make sure the talent itself is covered with green behind, even if the surrounding areas around the screen show something else (make sure to keep an eye on not making mistakes 1-4). Then in post-production, you can easily crop the non-green screen parts, and you are good to go.
The impact of green screens
Once you have these primary green screen do’s and don’ts figured out, you will be able to do virtually anything in your next production. It opens a world of possibilities so straightforward that you can improve simple Zoom video calls or something far more intense, like Keanu Reeves’ Neo saving the world.