Deriving key signal from foreground of video signal - using three=dimensional zone enclosed on all sides for increased colour possibilities

摘要

In a method for density the key signal that, for fed in video signals which correspond to one colour location within a selectable region, a first level is used, for other colour locations, a second level. The selectable region is a three-dimensional all-sides enclosed region. Two respective multipliers (13,14; 15,16) receive a chrominance signal and the sine and cosine functions of an adjustable angle. The outputs feed adders (18,19) and these feed an absolute value circuit (22,23). One of these feeds a further adder (26) direct, and the other via a further multiplier (24). The further adder (26) feeds a series arrangement of a substracter (28), a multipler (29) and a limiter (31). ADVANTAGE - Allows even colours of low saturation to be used.