Intro to Keying

From TV studios to film sets to the stage, keying curtains and backdrops, a.k.a. “green screens,” are the way to go when you need to digitally remove or replace a background from a shot. But which keying fabric or scenic paint is best for your application? Read on to learn more about keying.

What is Keying?

Keying or chroma keying is a production technique in which a specific color hue or chroma (typically blue or green) is digitally removed from a video scene and replaced or “keyed” with a different image. This technique allows television, film, or video producers to combine scenes or images from different sources into a single image or scene. Shooting in front of a colored backdrop (like a green screen) allows for easy removal of the backdrop and anything else in the shot that’s colored green (“Look ma, no head!”). The best known example of this technique is when your city’s weather person delivers the forecast in front of a weather map.

Keying Colors

Typically, the compositing of images is achieved by shooting against a solid green or blue background, but not just any shade of green or blue. Keying colors are available in chroma or digital variations. Chroma key greens and blues are darker and duller, while digital greens and blues are more vivid and pure.

Which keying color should I choose?

Usually, the background keying color is chosen based on a variety of factors like the subject’s proximity to the backdrop, the level of detail that needs to be separated, and the colors of the subject being shot; for example, if there is lots of blue in the subject, green would be a better choice for backdrop color.

Green

While mostly any color can be keyed using modern day software, green is still the gold standard. The reason for this is that cameras tend to capture more green information than they do for other colors. Cameras use the green channel to capture luminance. Because cameras capture additional information on the green channel, it's easier to isolate and remove. When lit properly, green backgrounds provide a balanced exposure and allow for a clean extraction. If your composited background is vivid and bright, green backdrops will almost always provide the best result.

Blue

Blue is also a great choice for keying color. In the days of shooting on film, blue was the standard. Blue lacks luminance because blue absorbs more light than green. This lack of luminance can be both a benefit and a disadvantage. When shooting on a blue screen, it’s easier to avoid casting bounce light onto your subject, which can be helpful. Unfortunately, it also makes things more challenging to correctly expose both backdrop and subject and achieve the contrast needed for a good extraction. Considering these factors, blue remains a great choice for a composited background which is darker in tone than the subject.

Chroma Key or Digital Colors?

Digital Green / Digital Blue

These days, it’s usually best to choose digital green or digital blue. Their vivid, pure colors allow for easier separation of subject and background. Digital keying colors really excel when fine details like wispy hair need to be extracted from a shot. Because digital colors are so bright and vivid, it’s usually best to employ them when a subject is being shot further from the background, as there will be less of a chance of the color reflecting back onto the subject. When this occurs, compositing software may interpret the reflected color as background and mistakenly eliminate.

Chroma Key Green and Chroma Key Blue

When a subject is being shot close to the background, duller, more subdued chroma key colors are your best choice as they will not reflect onto your subject as with digital colors.

Choosing a Keying Surface

Keying Fabric Backgrounds and Backdrops

When choosing a keying fabric, size is probably going to be the first consideration. Realize that in order to extract a clean image, fabric must be stretched so that there are no wrinkles. Keying fabrics are available in a variety of widths, up to 19’ wide. Once a size is determined, other considerations should include flame rating, reflective qualities, and color. Matte finishes are great for close up work while more reflective keying fabrics can be helpful with separating subject from background. Shop chroma key and digital keying fabrics here.

Painted Surface Keying Background

Scenic paint is also a great option for creating a clean keying background. Chroma Key scenic paint is formulated to provide rich color saturation and coverage so there’s no having to worry about wrinkles, as with fabric backdrops. Although creating an extremely clean keying background is easy with scenic paint, the disadvantage is the permanence of the structure. A fabric backdrop can easily be moved whereas a chroma key painted wall is a bit more difficult to manage. Shop chroma key paint here.

Whether you are looking for keying fabrics, a custom green screen, or scenic paint in keying colors, we’ve got you covered.