What is Chroma Keying?

Chroma01Chroma keying is the process or technique of replacing a solid background (the key) with another background or animation.

This can be done live or in post production editing session. Chroma keying is also called "green screening" or "blue screening", however, any color can be used as a key as long as it is not present in the foreground element being isolated by a computer editing program or live video switcher.

Why would you want to have a full body key?
Many productions use a chroma key shot that is a torso and up cropping which means that the talent is filmed from their waist up to above their head. The background is then replaced to place them in whatever setting is needed for the production.

A full body key is slightly different and a little more advanced than a typical torso up shot. This is because the studio room needed for the production is greater (where as a torso up shot can be filmed in nearly any room with a small green/blue screen backdrop). A full body or length chroma shot is one where the talent is standing on the chroma background and is filmed from head to feet.

There are a number of reasons that a full body chroma shot could be needed or desired for a video production. A few usesChroma02 might be for weather forecast productions, presentations, segment introductions or special effects work.

Regardless of the reasons for needing a full body chroma key shot, there are a few advanced techniques that can be employed during production to help with creating a clean key in live or post.
Supplies Needed:
• Lighting (foreground, background, floor lighting)
• Ample Studio Space (enough space for a chroma background to be curved to the floor and under the talent standing 5-8 feet from the chroma wall area.)
• High Quality Green/Blue Screen Chroma Background that Curves to the Bottom of the Floor and Beyond (A painted wall/floor can work in some situations, but plan on spending more time testing and in post production to remove your chroma key.)

Clothing Suggestions:
Chroma03You will want your subject to be wearing clothing that is not present in your background key. So if you have a green chroma background, avoid wearing green or blue/green colors which would confuse the live keyer or video editing software. If you have a blue chroma background, avoid blues and other hues that are closely related to blue.

Also, you will want your subject to avoid wearing light/white or shiny fabrics which can reflect the chroma key which can also give you trouble when you go to remove the key in your production. For Men, a dark suit or blazer works well to key out of a background. For women, a darker skirt and non-chroma colored top will generally work very well. Women can wear darker high heels and men can wear non-shiny loafers or other shoes which will key cleanly from the floor.
If you are getting chroma spill on the back of your subject, try to position them further away from the back of the chroma key area if possible. If the light spill is coming from the floor, try to adjust the intensity of the floor lighting to decrease the amount of reflected light hitting your subject. You can also add a back/kicker light above and behind your subject to further seperate your subject from the chroma key.
Lighting plays a crucial role in any chroma key production, but it is especially important on a full body chroma key setup. You will want to light your foreground and background separately and you may also need to light your floor as well to eliminate shadows and variations beneath your subject.
Light your chroma key background as evenly as possible with 2 - 3 lights positioned to the side and/or above your stage setting. Angle the lights down onto your background (this will reduce the amount of spill/reflection onto your subject). Diffused lighting tends to work best for an evenly lit background key since spotlights can create hot spots on the background. These hot spots are difficult to see with your eyes, but can cause issues during the final editing process. You can use light diffusers (homemade or professional) or soft boxes to create a softly lit chroma key background.

For your foreground/talent lighting, you can use more direct lighting or soft diffuse lighting depending on the light you are attempting to match in the replacement background image/video. Lighting can vary, depending on production needs, but generally is accomplished using a keylight, fill light and floor lighting (to remove shadows around the subject' s feet). Place the keylight in front and to the side of your subject. The fill light can go on the opposite side of the subject and may not be as intense of a light (but enough to offset the shadows caused by the keylight). The floor light can be setup directly in front of the subject at a slight angle. Do not light the floor light too brightly as this can cause reflection onto the legs of your subject. Just use enough light to reduce the amount of shadows falling onto the chroma material where the subject is standing.

Other Tips & Recommendations
There are a wide variety of techniques and shooting styles when working with chroma key video production. Here are a few more tips that can help your production create a professional finished product:
• Shoot in HD
Film at the highest resolution with the best camera you have available with the most manual settings you can find within your budget. Try to use a camera with manual iris, gain/iso and white balance settings. This will give you the control you need to create footage that is easily workable in your production pipeline. Also, use a high quality green screen material such as foam or fabric. Avoid shiny materials such as paper and paint if possible.
• No Wrinkles
Along with lighting your chroma key material as evenly as possible, try to avoid wrinkles and other variations in your chroma background that cause shadows and highlights. The more even and consistent your chroma background is, the better!
• Not TOO Bright!
The brighter you light your chroma background, the more likely for spill onto your talent depending on distance to your background, so be sure to light your chroma key background evenly, but not too brightly!
And finally, EXPERIMENT! The best way to get experience is to experiment. Test different lighting conditions, chroma key fabrics/materials, cameras, clothing, distances, software and studio setups. The better you understand your particular gear, the better your final product will become!
If you have any questions about this article or how it could be used within your educational setting, please contact me at [email protected]

Templates and designs used within this tutorial can be found at:
Robert Pancake is a animator and graphic designer specializing in broadcast production and design.