键控是利用一个视频信号中不同部位参量（例如亮度和色度）的不同，经过处理形成高/低双值键控信号，去控制电子开关，使待合成的两路视频信号交替输出，形成一个画面的一部分被抠掉而填进另一画面的效果，俗称“抠像”。-Keying is the use of different parts of a video signal parameters (e.g. luminance and chrominance) are different, after treatment to form the high/low two-valued key signal to control the electronic switch, to be synthesized so that two video signals are output to form a part of the effect of pull out and fill into another screen picture, commonly known as　keying.