Why is the background of movie special effects usually green?

Cameras are more sensitive to green. In the post-production of matting, the green background is easier to create and add special effects, which will not affect the quality of the film, and the fineness is higher than other colors, so most films are based on the green curtain.

First of all, the sensor of digital camera generally adopts Bayer array, so the number of green pixels in the camera sensor is twice that of red and blue, so it is more sensitive to green, and it is easier to capture the information of green pixels, thus reducing the difficulty of keying in the later special effects production, not easily overlapping with the required elements, and not affecting the color performance of the picture.

Secondly, the use of green curtain is wider, whether indoors or outdoors, there are fewer interference factors, while the color of blue curtain is similar to that of the sky, so it is easy to be disturbed in post-production, which will increase the difficulty of film production, including curtains of other colors, which will overlap with the required pictures.

Finally, the human body basically does not contain green, and the contrast between human skin and green is the largest, so it is more accurate when keying, which will not harm the overall picture color of the film, and will also reduce the workload and facilitate computer processing.

Working principle of green curtain

Green screen also has a name called color key technology, which explains its working principle. We can use a video production device called chroma key to view the chromaticity data.

If a pixel falls on a small part of the color circle centered on green, it will be recognized as a green screen. These parts of the video will be replaced by other pixels in the background channel, such as the weather map. Pixels of other colors captured by the camera will remain, such as orange (skin color), red, yellow, magenta and blue.

The result will be a video of the weather forecaster in front of the weather map. The green color in the background video has no influence at all, but if the person being photographed wears green clothes, this area will be cut off and they will become transparent.