The superimposition of moving images through special effects. This is a complex clipping technique where the line of separation is not necessarily a defined form but may be a displaced object. The signal for clipping is more often established in function of color than light. A saturated color is used, often a blue ground because of the distance it implies from the flesh tones of the subjects placed in the foreground. Video color overlay can be done live: if an actor is filmed on a blue ground, a second image source can be sent to a mixer that transforms it into a backdrop.