Understanding how to use a green screen is a must for a filmmaker.
It’s a tool that is wildly used not only for budgetary reasons but also to achieve the Director’s vision when things can’t be done practically.
When most people think of a green screen they usually think of movies like Star Wars or The Avengers or even the nightly weather report, but green screens are used in all kinds of films that you would never suspect to have them.
Very often green screen shots that go undetected are in films grounded in reality like Gone Girl or The Wolf of Wall Street. Understanding how to use a green screen will help you think out of the box and creative problem-solve as a Director or Producer.
Want to learn how to use a green screen? We’ll explore:
- Why green screens are green
- Shooting with a green screen
- The plate and backgrounds
- Green screen software
- Green screen for live broadcast
- Common green screen mistakes
- Resources for green screen use
So besides the realm of science fiction or superhero movies, in which you put Actors in green suits to replace their action with a CGI monster, or place a green screen behind an Actor to put them in a different physical world, what would you use a green screen for?
Well, if you are shooting on a soundstage, you might put a green screen outside the windows of the offices and homes, so the view can be added later or you might build part of a set and create the rest in post.
Most driving scenes are shot the same way – the trees whizzing by are composited in so the Actors can concentrate on performance and not worry about getting in an accident. You can shoot in a high rise of a small city and put a view of Manhattan out the window to set the scene in New York, or shoot on location, but add elements to it. There are myriad of ways to use a green screen to create the illusions we see in films.
So how does it work? It’s not as complicated as you might think. You shoot your subject in front of a green background (or blue, but I’ll get to that) so the green can be chroma keyed out. In a sense, what was green becomes translucent so it can be put on top of, or composited with another image. It’s definitely a fun thing to play with, so read on if you want to start experimenting with this effect.
The truth is you can use any color. However, green and blue are the most widely used. I’ll let Bill Byrne, Author of The Visual Effects Arsenal explain it: “[G]reen and blue are used because they are the complement of the colors that make up the base colors of human skin tone.
1” But why is green more popular? Is it better? Jeff Foster, in his book The Green Screen Handbook can also field this question better than I: “[T]he green channel in composite video has the highest luminance value of the three signal colors red, green and blue (RGB). . . so it gives you more data to work with2.”
Also, green is easier to light and is less likely to compete with eye color or clothes. The last thing you want to do is key out someone’s blue eyes! And if you are shooting a tennis match, you might want to use a blue screen or everyone will be watching an imaginary ball!
First, you will need a green background. This can easily be purchased online, but you can always create your own. Just be aware that the color needs to be consistent; varied shades will make the post process more complicated.
You will also need two three-point lighting set-ups. Why two sets of lights? You will be lighting both your Actors and the green screen. Which leads to the next important element – space. You want to have enough space for both lights and Actors or subjects, who should be at least eight feet from the green screen.
The reason for this distance is because you want to have enough depth of field to have your Actors in focus but the green screen blurred. Blurring the screen decreases the variation in the color, so it will be easier to key out. If you haven’t noticed, color changes depending on how light hits it.
You will want to light your talent first. Start with basic three-point lighting using a key, fill, and back light set-up. Then you want to do the same for the screen, making sure there are no shadows.
Now roll the camera! If you are using a DV camera – and very few of us are these days – be prepared that you won’t be able to get a perfect key (finished product). It’s not your fault. The media is not optimized for a good chroma key so you will get jagged edges.
The second element of a composited shot is the plate. This is the footage you will put “under” the footage you shot against the green screen, so when you key out the green, it looks like the subject is in the world of the plate. This is something you can shoot yourself, or you can purchase plates.
This is where the magic happens! These days our phones have apps that can do this, but in the film world, you still sit at a computer. Before I go on, let’s take a second to understand some of the post-production process.
An Editor cuts the film together and the VFX Department takes care of the effects. But in order to visualize the film properly, the Editor will usually do a temporary composite in the editing software that will eventually be created by the VFX team.
The point here is that you can create a composite in editing systems like Avid or Premiere, but in the real world it will most likely be professionally done in a program like After Effects. For the purpose of learning, I would use the program you are most comfortable with.
Whichever you decide to use, it’s almost as simple as putting your plate on the timeline, then putting your green screen shot on top of it on another video layer, applying an effect and pushing a button. Voila! The green is gone. If you shot it well, all you will need to do is some finessing in the effects palette.
Alright. I told you that your subjects should be eight feet from the screen, and you need three-point lighting and special software to build the shot, but what about the weather forecasters?
How is it that they are so close to the screen? How do they do all that compositing in real-time? The answer is — different software and a different setup. Mind you, it’s not cinematic, but it does the trick and it has for decades.
The weather forecaster stands in front of the green screen looking at a video screen that has the graphics they are referring to (and seemingly standing in front of) that they can change with a remote as they speak.
The software they use is called Ultimatte and it is so advanced that the talent can be close to the screen and cast a shadow. It will have no problem pulling the key to make a clean composite; and, get this, maintain the shadow!
I’m really big on the phrase, “Garbage in, Garbage out.” It’s my response to, “We’ll fix it in post.” If you don’t shoot a good green screen, it’s harder to composite.
Lighting is the number one cause of bad green screen shots, the biggest issues being uneven light, not enough light, or too much light. (Too much light causes the light to spill onto your Actor, making them look green.) The most common mistake I see is washed out backgrounds because the screen, itself, wasn’t lit.
Most of these things can be fixed, but that adds up to time and money. Other issues people discover too late are reflective things in the shot. The most easily missed are things like when Actors are wearing glasses or jewelry. So keep a lookout and check your monitor to avoid trouble later.
If you are ready to start playing, there are some great resources out there. Most stock footage websites like Pond 5 have green screen footage and there are also sites geared specifically to green screen elements.
Check out Pro Video Backgrounds. If you don’t have the resources to shoot something on a green screen, check out Green Screen Films. They have some great green screen footage to manipulate.
If you are interested in using your phone, take Chromavid for a test drive. You’ll still need to shoot your subject with a green screen, but there are fun backgrounds to fool around with.
Another one to explore is KineMaster. This app is more than just a compositing app. It’s an editing app as well, so if you are integrating your shot into a larger video, this is a good choice so you don’t have to use multiple apps to get the job done.
Green screen techniques can be very complicated and tedious. This is just the tip of the iceberg. There are so many layers to the processes and the possibilities are endless.
But knowing how to use the tools is an asset if you are thinking about an in-demand career as a VFX artist or a Film/Video Editor, or want apply these tools as a Director.
