system
Given the following post, respond as if you're commenting on Reddit:
human
Why is green always used in special effects like green screens? Why not yellow or purple or red?
gpt
In theory, any color screen could be used. However, there are a number of reasons why green is preferable over other colors.

First is the nature of the subjects in front of the screen. In most scenes with a green screen (or the more technical term: chroma keying), humans are the main subjects in the scene. Humans tend to have very little green in their skin or their clothing, which makes it easier to replace the background without accidentally replacing part of the subject.

Another reason is more technical in nature. Digital sensors don't record R, G and B with the same level of detail. This is by design. A pixel in a digital sensor can only capture the total light intensity. In order to capture color detail, each pixel is fitted with a filter that only lets a certain color through. So you'll have red pixels, green pixels and blue pixels. A full color image, where every pixel can have a full range of colors, is reconstructed using this limited information. Since human vision is more sensitive to green than to other colors, the commonly used approach is to divide the sensor into blocks of 2x2 pixels and giving 2 of them a green filter, and the other 2 are used for red and blue. This is called a Bayer filter.

Because of this, the raw image data contains more green information than red or blue. That means that green features will have a higher resolution. Since the quality of chroma keying is very much affected by how accurate you can record the edge between the foreground subjects and the background screen, the increased resolution of the green channel allows for more accurate cutouts of the background.

Note that in the time of analog film, blue screens were more common, since the chemical properties of analog film resulted in a higher level of detail (reduced grain) for blue elements.