Chromatic key signal generator for colour TV - has switch=over circuit linking second video source via controlled amplifier linked to matrix circuit

摘要

A chroma-key switch over circuit which consists of a chroma-key signal generator and a changeover switch with two inputs. The inputs are connected to two video signal sources. The key signal generator contains a matrix circuit which will produce a brightness signal for one of the video sources. There is a colour difference circuit to form a composite colour difference of the first video signal. There is also a threshold circuit which functions in conjunction with the chromatic signals. The second input of the changeover switch (20) is connected to the second input of the circuit for linking the second video signal source (5) via a controlled amplifier (24). The amplifier has controlled input linked to the output of the matrix circuit within the brightness signal via another amplifier with adjustable limits.