Why do special effects in movies have to be done on a blue background?

Blue screen technology is also called color key technology. To put it simply, by shooting objects on the same color background, the foreground and background are distinguished by using the special hue information of the background color, so that the background is automatically removed and the foreground is retained. It is widely used in the dynamic background synthesis of radio and television and the creation of movies and photography. Blue screen technology does not have to use a blue screen as a background. In principle, choose a color that the foreground subject does not have as the background. The correct use of blue screen technology can not only extract the foreground correctly, but also extract the translucent region and shadow region in the foreground.

Matters needing attention when shooting

Be sure to choose the right background color when shooting. Avoiding the color of the background curtain in the subject is the key to success. For common portrait shooting, because people's skin is between red and yellow, red, orange and yellow curtains can't realize the function of automatic matting. Generally, blue, green and cyan curtains are used, depending on the color of the subject. Your props need to pay attention to this, too. If the subject contains background color, the subject will become transparent and translucent after matting. If it is really unavoidable, it can be made up by post-repair.