Why is the background screen of science fiction movies blue?

There are two aspects in the selection of color keys: one is the color of the subject; The second is the photosensitive characteristics of the shooting equipment.

The first one is more obvious. The core element of the subject is usually human skin, so blue and green are reasonable, because "distance" is the farthest from skin color, which is conducive to later identification and selection.

The second is the key to choosing blue and green. Film is most sensitive to blue light, so blue is used more. The use of green is first because of the appearance of digital cameras. Green is more suitable for electronic photosensitive elements. It is generally believed that when shooting with a digital camera, the subject can leave a clearer edge on the green background. This is because green has a higher reflectivity and is not easy to "melt" into the main body. Domestic jargon is called "explosion" or "boom" (whether this word has not been verified), and the post-processing is relatively clean.

The problem of film is a bit complicated, which is related to the specific film type, shooting environment and photographic equipment. Many people think that movies are more suitable for using blue screen outdoors and green screen indoors-but indoor green screen usually needs a unified background light behind the screen, which can improve the capture of color keys in movies.

Now, movies are all blue and green. For example, when Peter Jackson remakes King Kong, the background of the picture on the ship is all blue, and it will be green when shooting in the shed, which can be seen in relevant documentaries.