Anyone who has seen a weather broadcast has seen the effects of a chroma key green (or blue) screen. Most people know by now that the weatherperson is not actually standing in front of a weather map. Instead, this person is standing in front of a green screen and it’s up to the producers of the show to replace that screen with an actual image – at least from the viewers’ point of view. The Blackmagic ATEM switcher makes this action a lot easier than it was in the past, so once you use this feature once, it should be a breeze from then on.
What Is Chroma Keying?
Chroma keying (or chroma key compositing) is a technique where two images are composited, or layered together based on color hues (the chroma range). Commonly called the video production or post-production phase, it involves replacing a green or blue screen with one of those layers, and even though green or blue are the most common chroma key colors, any color that is consistent and uniform can be worked with. Whatever color is used must not be duplicated with a person’s clothing or anything else in front of that camera. If that happens, the clothing will show the image (e.g., the weather map) that is replacing the green or blue color.
The Blackmagic ATEM mixer can handle the chroma-keying process very well and makes the process very simple. In reality, it’s just a matter of pressing the right keys and knowing when to press those keys. While there’s a little more to it than that, there really isn’t much more to it because Blackmagic makes it very simple even for non-techies. What will happen is simple: the presenter stands in front of a green or blue background, and the person in charge of the chroma-key process removes that particular color then combines it with another image. Thanks to the ATEM switchers now on the market, you get multiple keyers that allow you to combine multiple chroma key elements in real time. This includes live, graphic, and prerecorded elements as well, and you can do all of this at the same time.
How Does it Work?
For the purpose of this example, we’ll use the ATEM Mini Extreme to describe the chroma-key process, although all of the mini switchers can handle this process. With the Mini Extreme, you get four upstream chroma keyers, which means you can set up a total of four cameras and each one can get a keyer. The Mini Extreme actually gives you a total of eight inputs – four for the cameras and the other four that you can connect to a virtual set computer to use the rendered backgrounds.
With the Blackmagic ATEM mixers, you don’t even have to move your cameras. You can load pre-rendered still image backgrounds from the media pool and media players to fixed camera virtual sets. You can also set up macros to change your cameras and to load the right background into your media players. Finally, you can also use a DeckLink Quad HDMI and live virtual set software if this is how you choose to do it.
With the Blackmagic ATEM mixers, the chroma keyer is very powerful. It provides you with a color picker that allows you to sample background colors if you want the key parameters automatically generated. There is a foreground color corrector that allows you to match the foreground and background layers so the process is seamless and continuous, and you can use it for title overlays by simply creating graphics that have either a blue or green background. With four keyers in the mixer, you get a keyer per camera if you wish to get fixed screen virtual set production.
Most of what you’ll need to do can be done through the Media Manager feature, where you’ll go to Users, then Folders, then Downloads. In the download section you’ll find your still images that you’ll choose to use in place of the green screen. Once you choose the photograph you want, you can move it on the screen to coincide with the camera that has the green screen on it. The ATEM mixer allows you to zoom in on a section of the screen and move it around if you like, so if you have an object on the screen, you can use the ATEM mixer to move that object around on the screen.
The Blackmagic ATEM Mini Extreme, as well as the other Blackmagic ATEM mini mixers, offer perks that other mixtures (at least not reasonably priced mixtures) usually don’t offer. This includes:
- Ability to enlarge the bounding box so you get a better range of the gamut
- Better threshold
- Cleaner key
- Preview of color
- Spill suppression
The amazing part is that, even with the least expensive Blackmagic ATEM mini mixer, you get the ability to utilize the chroma key feature, and you can easily replace the green screen with any still image or live video input source. Once everything is connected and set up, the mixer and your computer screen make the task extremely easy. On the ATEM mixers, the buttons you have to press are mostly self-explanatory, so by simply pressing a few keys, the chroma key process is complete. Even people who have never used these systems before will have the process memorized in no time.
The Blackmagic ATEM mixers come with their own software that you can operate on your computer to make the entire process fast and simple. The mixers start at less than $300 and go up from there, but these are top-notch mixers that have features you usually only find in mixers with much higher prices. The chroma-key function is important not just for weather broadcasts but for many other types of productions as well, so knowing how to use it is crucial. Blackmagic makes it easy to get crisp, clean images and to replace any green or blue screen with the right image so that in the end, your broadcast looks more professional than ever before.