The use of green screens has come a long way over the past few decades. Technology that was
primarily reserved for Hollywood blockbusters and local news stations is now utilized by many
of your favorite YouTubers. Here, we’ll guide you through the entire process of using green
screen backgrounds from start to finish. We’ll talk lighting, cinematography, keying, and
Before we jump into how to use a green screen, let’s learn what a green screen actually does and familiarize ourselves with a few key terms.
Green Screen: Technically, this term refers to the colored background you want to make
transparent and remove from your shot. This is usually a single colored backdrop, which can be
any color, but is usually bright green because it is the color furthest away from human skin tones.
(Blue screens were frequently used in the early days with film, and might still be used in certain
cases.) Sometimes the term is used as a fit-all for the entire process of keying (see below).
Chroma Key: This popular term goes hand-in-hand with green screen. It’s the actual technique of layering, or compositing two images based on color hues. Every color has a chroma range, hence where the terminology comes from.
Keying: This term is used to describe the process of removing the green screen background in post-production using video editing software. When the green screen background has been keyed, it will be fully transparent. Then you can fill in that transparent area with a different image or video. The goal is to get the cleanest key possible, meaning there are no digital artifacts left on your image where the green screen was originally.
Spill: This often refers to the colored light that reflects back onto your subject from the green screen. When a green screen is brightly lit, the light can actually reflect that color back onto your subject. There are a number of steps you can take to prevent spill, which we’ll discuss below.
The principles we use for overcoming the challenges of green screen are based on those from years ago, before we had digital compositing and video editing software. As you can imagine, the tools have changed quite a bit with modern video advancements. Here, we’ve broken down the new rules for working with green screens.
1. Start with the right green (or blue) Use a non-reflective green screen material and look for colors such as “chroma key green” and “digi green.” These colors are toned to be ideal for use with green screens. Alternatively, blue screens can also be used, especially for replicating night scenes. Learn more about the green vs. blue screen debate to figure out which color is right for your shoot.
2. Separate your subject from the background Keep your subject at least six feet away from the green screen. This helps minimize spill and unwanted shadows appearing on the green screen background.
3. RAW is King Film with the highest bit-rate/least compressed codec you can. 10-bit color will be superior to 8- bit. ProRes 442 and 444 are always great options and RAW is even better if you have that ability.
4. Expose the background properly Light your foreground and your backdrop separately. It is also important to light your green screen backdrop evenly. Proper lighting exposure helps to avoid excess green lighting spill.
5. Eliminate motion blur Filming with a faster shutter speed reduces motion blur and helps provide a cleaner key. You can always add secondary motion blur back in during post-production.
In certain cases, you may need real props on set that your actors can reference. In behind-the- scenes shots you will often see tennis balls hanging on the green screen set. These provide the actors with visual reference points. Lighting is another huge consideration. Think about lighting your character in order to match the lighting of the environment they will populate. This will make a drastic difference when it comes to the final chroma key composite, and layering everything together.
Determining Scale This is the time to calculate the scale of your final scene and the best lenses for filming your actors. If you are planning on creating a wide-angle scene, it makes sense to film your subjects at the correct scale. This process primarily relies on knowing the field of view of the lens used to film the background element, which is often referred to as a background plate. It’s essential that you shoot both the foreground and background with the same focal length lens, or at least as close as you can guesstimate if you don’t know the lens used to film the background plate.
One thing worth noting is that the wider the background shot is, the larger the green screen will have to be in order to completely film your actors. Luckily, Mark Vargo walks us through this process in this article, which utilizes the lens field of view to calculate the final green screen size required for any shoot. The more notes you have from the original background shot (such as lens, time of day, etc.) the easier this process will be.
As a rule of thumb, wider shots that capture your actor’s entire body and action shots that require lots of movement will need a full green screen that also covers the ground, and maybe even the side of the shot. If this is the case, make sure the screen has no edges so that you can key in easily. You’ll want to use a curved screen and drops without hard edges to the floor or to side walls.
Prepping Actors and Objects You’ll have to prep actors and props for use on green screen. Obviously, avoid green! Actors shouldn’t wear green or they’ll end up transparent in the key. You should also avoid shiny objects, as these can reflect the green and cause transparent spots. If reflective objects must be used, you will likely have to manually mask around those objects in post-production. This can be very time consuming, so plan ahead if that is ultimately required.
There are three non-negotiable rules to lighting a green screen: • The lighting must be even • The lighting must be soft and diffuse • The green screen must be lit separately from the subject.
When lighting your green screen background, the goal is to get the lighting as even as possible. This helps ensure that the green coloring is even, with no hot spots or shadows, which will help with the chroma key process in post-production. You will also need to light your actors and the green screen separately, preferably with the actors and the green screen background at least six feet apart. Remember to match the lighting on your actor to the scene in which they’ll appear once the green screen is composited.
In this article on green screen lighting, you’ll find the key to even lighting is the same for achieving soft light in any other shooting scenario — use big, soft light sources. Hard light sources with no diffusion will create hot spots on the green screen background. To diffuse your lights, you can use on-light diffusion boxes or set up large silk frames. If you are on a budget, try using a white bed sheet mounted on a c-stand a few feet in front of your light.
The placement of your lights also matters. If you are only using two lights to illuminate your background, place one light on each side of the green screen, a few feet back on a 45 degree angle. You can fine tune/adjust the angle of each light to make sure they’re not overlapping too much in the center. Make sure you are using the same lights on each side of the green screen for consistency. On bigger productions, you may need to use overhead lighting, additional lights, or more diffusion, but the basic principles outlined here will be the same.
As mentioned, chroma key refers to the technique of compositing two images (or video clips) together based on color hues. And in our case, we are using a green screen to replace what is behind our actors. You will often hear the term “clean chroma key” when editors are referring to green screen composting. A clean chroma key composite is the end goal.
Preventing Spill A clean chroma key will leave the actors or subject with crisp, defined edges that look natural. But oftentimes, digital artifacts, jittery/jagged edges and color spill from the green screen can appear. Spill is one of the biggest offenders – it happens when the green screen reflects back on your subject, creating a green halo that’s hard to get rid of in post.
This article on clean chroma keying has some great tips and tricks that will help your chroma key results, including how to prevent spill with thoughtful planning. One of the first is deciding if you should use a green screen or blue screen. On today’s digital cameras, green will likely give you the cleanest key. However, if your actor has blonde hair or green clothing, you’ll likely have better results with a blue screen as green can spill into light-colored hair.
Using Motion Blur The whole point of the green screen process is to achieve sharp edges, and motion blur can undo this. For that reason, it’s best to film green screen shots with a fast shutter speed to eliminate motion blur. This may almost appear as a stuttering movement on the actors. You can fix this by adding motion blur back onto your actors in post-production. You can use CC Force Motion Blur in After Effects or try the third-party plugin ReelSmart Motion Blur. Adding motion blur back on your composite will make a noticeable difference.
Film with a Low ISO You also want to make sure you film your green screen scene with a low ISO setting – we recommend the lowest ISO setting your camera has available. This is because higher ISO levels introduce noise artifacts and those will appear on the green screen background. This can result in a lot of “off-color” spots on the green screen background that can make the keying process more difficult.
Lighting a green screen is fairly simple from a technical perspective, yet many DPs who don’t
have much experience with chroma key work are prone to making some unfortunate mistakes on
set. Unlike traditional film lighting, which is all about finding contrast and mood by balancing
light and shadows, lighting a green screen is all about evenness and consistency.
For the purpose of this post, I’ll describe a basic green screen lighting setup that involves only two background lights. While two lights might be all you need for many scenarios (such as an interview setup), keep in mind that the basic principles outlined here can be applied to wider and larger green screen setups too — you just may need to add more light.
The most crucial thing to remember when lighting your green screen: any area of the backdrop that appears in the frame must be lit perfectly even and exposed correctly. If your backdrop is lit properly on one side but underexposed on the other, your compositor or editor will have a very tough time pulling a clean key. The same applies to a backdrop that’s either over or underexposed. Any attempt to pull a key from a backdrop that isn’t actually reading as green on camera will inevitably be a failure.
The key is the same for achieving soft light in any other shooting scenario — use big, soft light sources. If you point a hard light source (such as tungsten light with no diffusion) at your green screen, you’re going to run into trouble. The light will have a hot spot and there will be a gradient surrounding it, ultimately giving you an uneven light to work with.
Conversely, if you were to point a tungsten light (let’s say a 2K source) at the green screen, but use a large 8 x 8 frame with a silk to diffuse the light, you’ll be in great shape. Personally, I prefer to use double diffusion when shooting on a green screen. My ideal setup typically involves a bright light source that’s first diffused by a standard 4 x 4 silk on a C-stand, and another 8 x 8 frame in front of that silk for an additional layer of diffusion. This ensures that the light is as even and soft as possible.
Assuming your needs are relatively simple, you can use a minimum of two lights to illuminate
your backdrop. Using the setup described above, I recommend placing one light (with diffusion)
on either side of the green screen, a few feet back on a 45 degree angle.
Right off the bat your results should be pretty close, and you can fine tune/adjust the angle of
each light to make sure they’re not overlapping too much in the center. In other words, you don’t
want to have a hotspot in the middle of your frame if both lights are spilling into each other. Be
sure to adjust your lights and use flags when necessary, so your lighting is as even as possible.
It should also go without saying that you’ll want to use the exact same lights on either side of the green screen for the sake of consistency. If you’re using two different lights, you could run into exposure issues (or even worse, color temperature issues) which could once again cause headaches in post. With regards to the rest of your lighting setup, these will be creative decisions and are ultimately up to you.
If you want a more dramatic look on your talent, you can light them from the side. Alternatively, you might use two more flood lights on the talent’s face to create an even flat light. No matter what creative look you’re aiming for, the green screen will always need to be lit the exact same way.
or decades, green screen technology has been used to create some of the most awe-inspiring special effects seen in your favorite movies and TV shows. Valera is now making this same technology available to you — at a fraction of the cost. We make it easy for you to wow audiences by immersing yourself in any imaginative background or setting of your choosing. Our mission is to empower your creativity with ultra-portable, high-quality green screens at an affordable price.
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