针对视频编辑软件中的色键效果算法，从理论上进行了深入研究。通过 数学建模，得到了求解前景中视频对象的蒙片方程和通式，在分析特例的基础上，提出了一种双前景抠象技术，并给出了相应的定理及证明，利用它可将任意颜色的视频对象从任意底色中抠出，并通过C语言编程实现了该技术。

Key color effect is commonly used in video and film editing.In this paper,the concept of Alpha channel has been described and algorithms of the key color effect have been thoroughly studied theoretically.A mathematical model that foreground image can be seen the overlay of the video object and background of this image has been established.Based on this model,the matte equation and its general formula are obtained.By discussing the special case that a desired foreground video object is separated from two backgrounds of constant color (blue and black),a double foreground technique has been presented.Corresponding theorems that can pull a matte on any color object against random backing have been given and proved.We pulled the foreground video object from a complicated background and even object that includes backing color from constant color background by this technique with C language programming.Any other key color effects cannot realize these.