Abstract: A linear color television compositing system of the "blue backing" type, in which the foreground signal channel is always open. The foreground and background channels are not switched by the edges of the pictorial subject matter.The hue of the colored (typically blue) background is removed by vector subtraction and the luminance thereof by arithmetic subtraction.Flare illumination of the foreground subject(s) from the backing is removed, improving color fidelity.The background pictorial scene that takes the place of the removed colored backing area is linearly turned up or down, allowing shadows of foreground subjects to appear in the background.

Abstract: The linear foreground and background compositing system of the "blue-screen" type and as included in my prior U.S. Pat. No. 4,100,569, is provided with non-linear background control signals for improved composite picture quality under various adverse circumstances. More particularly, the problem of footprints, scuff marks, and dust on the "blue-screen" background for the foreground signal has been eliminated by a "clean-up" circuit 98 which shifts the background signal to "fully on" when it reaches a level in the vicinity of 80 or 90 percent "on", and making a concurrent reduction in the foreground signals, so that above the selected control level shadows or semi-transparency objects are made fully transparent and are not reproduced. The problem of "print-through" in the case of glossy black objects has been avoided by a circuit 34 which reduces background signal to zero when the level of blue foreground signals drops below a predetermined level.