What is a Chroma Key and how to use it

Have you ever looked at the weather maps that appear behind the weather presenters? Have you not hallucinated with those Hollywood blockbusters developed in magical or science fiction settings? The answer will surely be affirmative and in this article we will see what Chroma Key is and how to use it .

What is the Chroma Key?

Chroma Key is basically a backdrop that is placed behind the actors in order to, in post-production, be able to eliminate it simply and precisely to replace it with another according to the scene that is being shot. For example, what was mentioned in the introduction; place a weather map, a scene in outer space or any other scenario.

Chroma Key Types

Currently, the two most widely used Chroma Keys are blue and green in color as these colors are the furthest from human skin. A few years ago, the priority was blue, but it presented some problems, such as whether the actor had blue eyes. This caused that by removing the background in post-production, the actor’s eyes were also removed.

That is why the green color Chroma comes into play , along with the current technology of video cameras that, to simulate human vision, have greater sensitivity to green color.

How does Chroma Key work?

It is a technique that greatly facilitates the substitution of backgrounds in both video and photography projects but it must be applied correctly following several guidelines in order to obtain the optimal result.

Subject / Object Distance to Chroma Key

We must separate the subjects and objects that we are going to cut from the Chroma at a suitable distance to avoid the bounce of light from them and therefore color contamination, which would complicate their extraction or obtain a strange result with shades of color. of the background in our protagonists.

Chroma Key lighting and placement

The backdrop must be perfectly placed, stretched, without wrinkles and illuminate it evenly. If we leave wrinkles, even if we illuminate it well, it will produce shadows, which will expand the range of color tones of the Chroma, making it more difficult to select. If, on the contrary, the Chroma is perfectly stretched but we do not illuminate it on a regular basis, the color range would also be expanded, having the same problem in post-production.

Choosing the Chroma Key type

It is not imperative to always use green as we may be shooting a scene in which there are green elements next to our protagonist, such as vegetation. In this case we should use blue, despite the greater sensitivity of the cameras to the color green, otherwise it would be a hell of a matter to extract those elements of green color since by default they would be eliminated in post-production having to resort to frame editing at frame.

Caring for the wardrobe

The wardrobe should lack the color of the Chroma Key that we are using and, if possible, have well-defined edges so that it feels more clean and professional.

If we strictly comply with all these premises we will have an incredible result that will give us infinite creative possibilities. We just need light, a blue or green Chroma Key , our camera and something to tell.

 

Leave a Comment