WHAT IS CHROMA KEY?
Chroma-key technique (commonly called green screen) is a way to put you on the planet Mars if that’s what your video script calls for. In the picture below, you can see the green taken out and the other setting, a still picture inside The White House, replaces it.
Chroma-key is cheap and easy if you have the right equipment. Chroma key is probably the single most popular digital video effect because it lets your imagination rule your video production, not your budget or location restraints. Green screen can transport you from Mars to the American Revolution in the punch of a button.
- Chroma means color.
- In video, key means to put one image on top of another and make them one.
Chroma key means you remove any one color from your image and replace it with any image you want. A still shot of the planet Mars downloaded from NASA, or a video with gruesome battle scenes on the Potomac.
WHAT COLORS ARE USED?
Bright lime green and bright turquoise blue are the most commonly used colors for chroma-key, which is where the common name green screen comes from. If you stand a person in front of a lime green background, all the green can be removed and replaced with whatever image you want.
Because green and blue are so commonly used, many people think those are the ONLY colors that can be used. Not true. Any color will work with chroma key. Blue and green are chosen often because they are furthest away on the color spectrum from face tones.
YOUR WEATHER CASTER USES GREEN SCREEN
One of the main uses for chroma-key in television that you’re no doubt familiar with is the weather report. Next time you watch a TV weather report, you’ll know that the different maps, satellite and radar images appear behind the weather caster because of chroma-key technique.
The image of the weather caster is captured with one camera and in that shot, you can see the green screen. If you were to stand in the studio, you would easily see the weather caster standing in front of the green screen, perhaps the walls and floor are painted green, so the weather caster is walking right on top of the green.
The weather radar, satellite or other maps are all separate video inputs that the director will insert to replace the solid green behind the weather caster. The weather caster is watching where he is by looking at a monitor that’s placed slightly off camera and shows the blending of the two images. The viewer never sees this monitor.
A good weather caster will shift his head toward the green screen, but his eyes go toward the monitor. This way, it appears he’s looking intently at his map, but he’s really checking to see if he needs to take baby steps or big daddy steps to reach California on the map.
Lots of weather casters doze and think they’re talking about snow in Milwaukee when the viewer is seeing them on top of a radar image of Miami. The weather caster never knows the difference if he doesn’t check his off-camera monitor, but the viewers think he flunked geography.
You’d be amazed at how often chroma key is used. It’s not just for the weather report. When taking a tour of the ABC studios in New York with my high school students after we won our Emmy, we watched a news update go live. The anchor person was actually in a TINY green screen room, smashed up against the wall. But on the air, they looked like they were in a HUGE, elaborate studio. It was seamless. There was NO indication in the final shot that it was a chroma key. (You can tell by looking at the edges of the person against the background. You can often see a green tinge or reflection.) I was blown away by how realistic it looked, and I’m not easily impressed.
HOW DO YOU DO GREEN SCREEN?
In a studio, most green screen is done live through a video switcher. But green screen can also be done with advanced computer editing programs. Most advanced programs have the capacity to use any color, not just green. You can use brown if that’s what works for you.
Lime green and bright blue are the preferred colors because they’re on the opposite side of the light spectrum from skin tones. You don’t want someone’s face being replaced with the weather map! But if you want to chroma key a green alien onto Mars, a brown screen instead of a green screen may be the way to go.
Whatever color you decide, videotape your subject in front of a flat wall that’s solid with that color. Light your video with bright, diffused light on the background, so there are no shadows. Any variation of the color behind your subject will be difficult to work with. Any shadow falling on the background creates a slightly darker color, which might confuse your edit system. Hot spots will create a brighter color your system won’t recognize as the chroma key color.
Once you get a solid, even-colored background, your switcher or edit computer can completely remove that color, and you supply a substitute. The precise mechanism by which to accomplish this will vary from system to system.
FOOD FOR THOUGHT
- In your own words, define chroma key.
- Why are blue and green commonly used for the chroma key effect?
- What can you look for the next time you see your local TV weather report?
I was wondering how they chroma key the weather when its on air
Hi Nate
Thanks for reading video production tips.
The weather report is one of the best examples of chroma key found on television.
The maps, radar, and satellite images replace the solid green background behind the weather person. The weather person has a little monitor off camera they look into in order to see where they are on top of the maps. If you were inside the tv studio, you would see the weather person standing in front of a solid lime green background. The backgtound is not very big, probably about 8 feet high and five feet wide.
Most weather casts are done live, so the camera signals and other images are processed and mixed through a video switcher. The video switcher is a piece of equipment that is used to “edit” a live tv show. The video switcher has tons of buttons and every video source available is hooked up to it. The director punches the buttons of the images wanted at any particular moment.
Thanks again for reading video production tips.
Lorraine Grula
i have a question. i have heard that a sophiticated technology is needed for green screen mate(chroma technology) is it so, then what may be technology.
Hi Udaya.
Chroma key, or green screen technology, is pretty sophisticated by itself. You do not need anything beyond that, but simpler editing programs do not have it.
Green screen comes into the process through either video editing software or a machine called a video switcher. You videotape in front of something green, then take all the green out and replace it with something else. The more sophisticated versions can let you use any color, not just green.
Thanks. Hope this helps you.
Lorraine Grula
Thanks for the tips. I’m new with this. It makes me more understanding.
Now am finding a Chroma key live switching. Not found yet.
Chroma key will be on most, if not all video switchers. It might also be called color key. The color key function will even be on the smaller, less expensive switchers. Good luck!
Lorraine
hey does anyone know where i could get a weather map to put on my blue screen??
You want a real weather map?
We are manufacturer in china focus on the green screen technical and chroma key system about 8 years. we improve the following system .
Servicenter (@) 126.com
Virtual karaoke studio is a new, innovative, funny and mesmerizing form of Video game machine. Participants can see themselves on a TV monitor while they singing.It breaks through the traditional mode of Karaoke singing.
Servicenter (@) 126.com
Everyone loves seeing themselves being replayed on the screen . All participants receive a DVD copy of their performance to enjoy at home with family and friends. or upload to Face book/ YouTube/ Cellphone/ Broadcast on TV etc. Every one can be a star, no talent required.
Servicenter (@) 126.com
That sounds like fun! I’ll bring my ear plugs. 🙂
Loraine
Can you help me find someone to chroma key my video. I would like to edit my video (a spokesperson) seminar to have a transparent background so I can insert it into my powerpoint presentation. I don’t want to learn how to chroma key edit… and am on a low budget…
thank you!
Hi Bonnie.
Did you shoot this video already? To do green screen you have to shoot your speaker in front of a green background and then you take out the green and replace it with another image during editing. If you shoot someone speaking at a seminar, that would be difficult. Especially if they walk around while speaking.
If you want to find some video editing professionals to help you, go to the website http://www.spidvid.com where they have developed a community of video professionals. You could find someone to hire there.
I hope this helps.
Lorraine
I have filmed and edited a video featuring someone in front of a green screen. However, we inadvertently included a product image in the video with some green in the packaging. This of course was edited out with the chroma key process. Is there any way to keep that small amount of green or is it a lost cause – and we’ll have to reshoot? Any help would be greatly appreciated!!! Thanks!
Hi Sarabear1014
Bummer! There are three things you could do.
1. Re-shoot. If you want to use the same product in the shot, you can use a background color other than green. That is, if your edit system accepts other colors.
2. Live with it the way it is.
3. In editing, add a second video line with just the product matted out and showing. This will cover the product in the original shot. In the second clip, you can adjust the chroma key down so it is not as sensitive and perhaps will look better. This will take some time to do and the matt may be hard depedning on which program you are using.
I hope this makes sense.
Lorraine
I am a high school teacher and started doing our daily news program last year. We had a lot of success using a green screen and imovie as well as final cut express to do a taped version of our news cast. This year, we are going live! I want to keep using our green screen with our virtual sets. What equipment/software do I need to make that happen? Thanks!
Hi Bree.
I was a high school video teacher myself a few years back. You would need some kind of video switcher. A video switcher is used to “edit” a show live. The switcher I had in my classroom was very small but it would do a chroma key. I hope this helps.
Lorraine
Am greatful coz ur article made me really understand the concept of chroma key.can i download a weather map from internet and use it for my chroma key?
Hi Lawrence.
You might have copyright issues if you just download an image from the internet, but on a technical level you could do that. With a real weather cast, the weather maps are live images.
Thanks for reading VPT.
Lorraine