Why does the movie green screen use green?

The movie is green, but foreigners' glasses are blue? Want better photos? This idea is really outrageous. In fact, the green picture of a movie is usually influenced by two reasons. One is historical reasons: when color film was first invented, its image was green, which was determined by the film structure. The film is mainly divided into four layers: blue layer, green layer, red layer and base layer. The green layer is easier to develop, so the film is generally green, commonly known as film green. Later, various manufacturers also produced some other color-cast films, but the mainstream films still tend to be green.

Second, aesthetic tendency: Due to the historical reasons for the greening of movies, and people's eyes are more sensitive and comfortable to green, green pictures have become the default standard of image aesthetics, which directly affects the film production in the digital age. In Hollywood, an upscale turquoise &; Orange style, namely blue-green tone+orange Huang Tiao. Blue-green tone, mainly used to decorate the background (sky, plants, walls); Orange Huang Tiao is mainly used to decorate the foreground (skin, yellow car, desert). Like the Transformers Iron Man. Because of the digital camera, there is no problem that the film is green, so these films are all made by color matching software in the later stage.

In the era of monolithic cmos cameras represented by ARRI and red, many green screens are used because there are two green photosensitive spots on Bayer array, which has the largest amount of information.

Bayer array is one of the main technologies to realize CCD or CMOS sensor to shoot color images. It is a 44-array, which consists of 8 green, 4 blue and 4 red pixels. When converting a gray-scale image into a color image, it will use a 22 matrix to perform 9 operations, and finally generate a color image. The array has been patented by 1976. The above is from Baidu Encyclopedia)

In addition, the brightness of green background is higher than that of blue background, which is also an important factor for lighting engineers.

Technically, the amount of information in the two green channels is twice as much, so in theory, the light on the green background is half as much as that in other colors (don't underestimate this lighting, a space light with a large area of 6000W generally needs at least 8 lights, that is, 48k-48kWh/ hour, plus other lights, it needs at least 60- 100K, and 3 yuan can be counted as 65438 per hour. ! If you lose half the lights, you will save a lot of money! As for the one with black back, white back and gray back, it is not a color key, because these colors are all gray, so the brightness key is used for keying.

And the eyes are blue or green, which is actually very easy to handle. Generally, just do a mask tracking. The edges of the object are all processed. Are you worried that it is not easy to dig in the middle? What I fear most is the problem of synthesis! Therefore, there is a consensus in the field of green background synthesis that "the part that comes into contact with people can be as realistic as possible". Clean green can make the later key makers not want to throw sulfuric acid on the director!

Then why can't foreigners use a blue background when their eyes are blue?

In fact, the early keying was mainly used in the field of television, mainly for announcers to take pictures, so (note, this is the key point) keying can only be done in real time with a color key generator (we usually call it a stunt machine). He can only handle the key of one color, and there is no way to add other effects. Therefore, when foreigners with blue eyes broadcast news, their eyes are really likely to be cut off! Therefore, this statement is an old problem left over from the TV era. .................................................................................................................................................................