GB1425453A - Control and mixing of video signals - Google Patents

Abstract

1425453 Television PYE Ltd 30 Aug 1973 [4 Sept 1972] 40963/72 Heading H4F Apparatus for the control and mixing of video signals comprises a plurality of combined fading and keying circuits connected to respective isolated video signal sources together with control signal generating apparatus controlling the fading and keying circuits such that the gains of the latter (1) remains constant; (2) slowly change between predetermined levels or; (3) switch between predetermined levels, the outputs of each of the circuits being connected to a common output point. As shown, (Fig. 1) individual ones of a plurality of video signal inputs V1, V2-Vn are connected via respective isolating amplifiers 1, 2-10 and respective delay devices 11, 12-20 to respective facing and keying circuits 31, 32- 40 and to respective ones of a duplicate set of fading and keying circuits 51, 52-60. Each fading and keying circuit is controlled via respective driver circuits 21, 22-30 and 41, 42- 50 by means of signals generated in a control unit 265 to produce the various fading and keying operations indicated above. Outputs of opposite phases are produced on conductor pairs 261, 262 and on conductor pairs 263, 264 supplying respective output amplifiers 266, 267. Control unit 265 includes circuits to derive a keying waveform from selected video inputs either from the luminance component or from the colour signal through a chromic keyer and the unit may also include filter circuits to "slow" the edges of the keying waveforms to produce soft-edge effects on the display. Details of a fading and keying circuit are given with reference to Fig. 2 (not shown).