Whether you're itching to put yourself or your actors into never-before-seen environments for a new sci-fi project or just want your co-workers to not realize you've been working from Hawaii for the last six months during your weekly Zoom meetings, chances are you've started looking into either green screen or blue screen technology.
However, the most common question people have when they start looking at background replacement technology is, "What's the difference? Why would I use one over the other?"
We’re here to break down everything you need to know about blue and green screens and help you make the right choice to fit whatever filmmaking project you may be working on.
Main Differences Between Blue Screen and Green Screen
It seems overly obvious to say, but the key difference between blue screen and green screen is their color. They are both used for a technique called "chroma keying" and are most commonly used for background and object replacement in a shot.
They can both be used on the micro or mega-scale, and you will see both used in everything from the daily weather report to Hollywood blockbusters.
What is Chroma Keying?
Chroma keying is a technique where two images are layered or composited based on a certain color hue. "Chroma" refers to the color, and "key" refers to the removal of a specific element or area.
In post-production, chroma key software is used to identify a color that you want to "key out" and replace with another image or color.
Why are the Colors Green and Blue Used For Chroma Key Compositing?
While nearly any background color can be used for chroma key compositing, there are some very specific reasons why bright green and vivid blue are the two most common and widely used colors.
When chroma keying was first used in the earlier days of film, blue screens were the most common. This was first because, with film, the blue channel has the least amount of color grain and thus would result in a cleaner matte around the edges of the objects not being keyed out. It also renders as bright white when exposed on black and white film, making the footage compositing process very simple for processes that involved using an optical printer to composite film together.
Since the shift towards digital cameras took the industry by storm, green screens have become the background of choice. Green is the furthest color from human skin tone, which prevents skin tones from rendering improperly. Digital cameras also capture twice as much green color information as they do for blue or red because the cameras use the green channel to capture the luminance readings, which makes green easier to key out in post-production than blue.
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What is a Blue Screen?
A “blue screen” is a single-color blue backdrop that is placed behind an object or performer to be later keyed out in post-production and replaced with another object or scene.
What is a Green Screen?
A “green screen” is a single-color green backdrop that is placed behind an object or performer to be later keyed out in post-production and replaced with another object or scene.
Pros and Cons of Using a Blue Screen
As we briefly outlined before, there are several pros and cons to using a blue screen.
Pros:
- If you’re shooting on film, blue has the lowest color grain distortion and thus results in a cleaner matte.
- When shooting on black and white film, blue renders white, making optical compositing easier.
- Its lower luminance makes it great for shooting darker scenes such as night scenes.
- Less color spill helps when you film subjects with small details, which is retained after blue is keyed out in post production.
Cons:
- The color blue has less luminance, which means it requires more lighting to get a nice, even illumination necessary for chroma keying. This makes it a slightly more expensive process over a green screen.
- It can cause problems in post-production if there are any other blue elements in a frame, such as an actor's eyes or the ocean.
Pros and Cons of Using a Green Screen
Pros:
- If you're shooting with a digital camera, green screens are the easiest to key out in post-production, thanks to the camera collecting more color information.
- It’s cheaper to shoot on a green screen because of its high luminance, which means you don’t need as much light to produce nice, even lighting.
- It’s the furthest color from human skin tones, resulting in little to no skin tone color distortions.
- The spill from green screens can also make compositing subjects into a daytime scene easier, given green is bright.
Cons:
- Color spill. Because green screens have higher luminance, they’re easier to light, but they tend to bounce back more color than a blue screen. Shooting with a green screen requires a strong understanding of this process and how to control it.
- Its high luminance makes it less ideal for dark scenes such as nighttime.
So... Which One Should You Use?
When it comes to shooting with a chroma key background, the choice of blue or green comes down to answering some key questions:
- Will I be shooting film or digital?
- Is the scene intended to be brightly or dimly lit?
- Can my lighting budget accommodate more lights if needed?
- Do either of these colors exist prominently in other elements of the scene, such as wardrobe or props?
As a good rule of thumb, if you're shooting on film or shooting a dimly lit scene and you can afford the added costs of a blue screen, you might want to head in that direction. For most other purposes, green is probably the way to go. Most post-production software defaults to green for chroma keying, and you won't have to spend a ton of money on extra lights to get a usable result.
Tips for Shooting with Blue and/or Green Screens
There are many great YouTube tutorials and other courses that you can use to help you perfect your chroma keying technique, but here are some key tips to keep in mind:
- Make sure your blue or green screen is evenly lit. Having areas that are lighter or darker than other areas will result in uneven color distribution and make it more difficult to key out in post.
- Make sure no other elements in the frame are within the same color range as your blue or green screen, as these will get keyed out as well in the post-production process unless you take extra time and effort to mask them out.
- Pay close attention to color spill bouncing from your green or blue screen back onto your other elements in the frame. Use flags and other lighting modifiers to ensure that no green or blue "halos" are being cast on other people or objects, as this will result in rough edges in your final product that "give away" the green or blue screen.
- Use separate lights to light your blue or green screen than you do to light other elements to avoid shadows being cast by other people or objects in the scene that will be difficult to key out.
Once you've mastered the techniques behind chroma-keying, there is literally no limit to what you can create. Chroma keying has been used to create massive, immersive worlds on screen, as well as bring in objects that don’t exist, such as dragons and other mythical creatures.
Or, again, you could just use it to create a convincing background of your home office, so your production coordinator doesn't start questioning how you got so tan if you're working from your home in Chicago. We're not here to judge.
If you’re looking for a better way to bring your remote editing team closer together and collaborate more efficiently from a distance, check out Evercast. Evercast allows you to stream your edit sessions in HD while video chatting and exchanging notes with your team, all under one platform. Because we believe collaboration is the magic behind the movies.
