Why do you want to put green cloth in the background when making special effects movies?

Reason: This is mainly to separate the background from the foreground, which is convenient for later matting and adding computer special effects.

Application of curtains:

Sometimes a blue background cloth is used in filming. Let me give two examples:

1. It is necessary to take photos related to the army. Soldiers wear green military uniforms and paint green camouflage patterns; In this case, you need to choose a screen with a blue background.

2. In the future, shots with sci-fi themes will use a lot of blue tones, so it is necessary to consider using green as the background.

Extended data green screen principle:

In terms of light processing, because the shooting background is only a green screen, unlike the final shooting, in practice, the green background of key images is separated from the previous shooting area, so the most common and safest way to use light is to separate the background from the shooting area.

The first is to illuminate the background, that is, brighten the green background used for keying and process it into brightness that is beneficial to later keying, so that the camera can record and restore the background color correctly.

In fact, the most important thing is that the light should be evenly distributed without shadows. When choosing green curtain materials, we should try to avoid wrinkles and dark corners on the curtains.

But when there is something wrong with it, we can also find ways to remedy it: when shooting, the light distance between the foreground and the background should be as far as possible, and it is best not to affect each other. Because there is a distance between the foreground and the background, and the lens focuses on the subject, the green screen is usually blurred in Jiao Wai, so even if there are some flaws, it is not easy to see.

References:

Baidu encyclopedia-green screen