Green screen vs blue screen. When it comes to digital compositing, how do you know which background color is right for your video project?
For newbies, let’s jump into the basics first. Chroma keying is the process of shooting video on a solid color background and then digitally removing this background during the editing/post production process. Once the solid color background is removed, you can ‘swap’ the background of your footage – a technique that’s used often in news and VFX work. So, while ‘chroma keying’ is the post-production work, shooting on a screen on set is the first part of the process.
Most pro video setups use a green or blue screen background – but why? And what color background is best?
Image of Spiderwick Chronicles Blue Screen, Creative Commons/Wikimedia
Why Are Blue and Green Screens Common for Compositing?
To understand the basics of why green and blue screens are the most popular choices for chroma keying, we must first understand how a digital keyer works. With modern keying software like Keylight or Primatte, you can select a desired color range (chroma), as well as brightness range (luma), and ‘subtract’ this part of the image from the video frame in your editing application. This clip is then layered above a solid background clip in a video editing timeline. The result is the background clip will appear on the deleted parts of the image.
This image from Mark Spencer’s FCPX chroma key tutorial shows how this would look in a timeline.
More info on keying in Final Cut Pro X over at Macworld
Blue and green are on the opposite end of the color spectrum from red and orange, the main colors in skin tones. In fact, skin tones do not naturally contain any blue or green, so by using blue or green you’ll have less interference when keying a person on screen.
The biggest consideration for blue screen vs green screen is the color of foreground costume, objects, etc. It is imperative that the colors in the foreground of your video are not in the same color range as your blue or green screen. If your talent has green in their outfit and they’re against a green screen background, the green parts of the outfit may be removed when you key out the background. If you’re working on a large-scale production against a screen, decide early on the “illegal color range” for any objects in front of the screen!
Using the same colors when shooting is a technique often used for VFX work (motion capture, for instance). Here’s an extreme example featuring Ewan McGregor. Once the key is pulled, you’ll be left with nothing but Ewan’s floating head!
Image from Just Jared / Jimmy Fallon
But the choice to use green screen vs blue screen extends beyond just the outfit choice of your talent. Here are a few reasons why you should pick one over the other.
When to Use Green Screen
With modern digital cameras, the green color is processed the cleanest with the most luminance. The result is that you’ll often be able to pull a clean key with the least amount of noise, and often, without a complicated lighting setup. Conversely, because of green’s brightness, it can also lead to more ‘spill,’ meaning the green color may reflect and bleed over on your on-screen talent.
This can be a nightmare when keying out in post-production. To combat this, ensure that there is sufficient distance between the talent and the green screen background.
Green is also an ideal choice if you’re compositing in a ‘daytime’ background. Any leftover green can blend better into daytime footage, while it’s more challenging to blend green against a darker (or nighttime) background.
When to Use Blue Screen
Blue screen will require twice as much light as green screen, often a whole f-stop. But because of this difference in luminosity, blue also results in less color spill. Blue screen is also ideal for replicating darker or nighttime conditions.
Often, color correction against a blue screen is cleaner than its green counterpart. The spill of green can result in some messy color work in post that can eat up your time in the edit bay.
Regardless of what color screen you use, shooting in a more uncompressed (or RAW) format will ensure that you have more data in the shot and will likely result in an easier time when you go to key out the footage in post.
For more of the nitty-gritty technical details of green screen vs blue screen, check out this post over at Animation World Network.
More on Green Screen vs Blue Screen
This tutorial from PremiumBeat gives a great rundown of the key differences between shooting on green screen vs blue screen.