Patent GB-1286052-A (GB)
Title: Electronic composite photography
Inventor: VLAHOS PETRO
IPC: H04N9/75
Filed: 1971-03-16
Abstract: 1286052 Television ASSOCIATION OF MOTION PICTURE & TELEVISION PRODUCERS Inc 16 March 1971 6983/71 Heading H4F An electronic system for producing a composite colour picture from a foreground scene 10 and a background scene 32 in which the background 12 of the foreground scene is illuminated 16, 17 with light of a predetermined colour e.g. blue, includes means for simultaneously scanning the two scenes (e.g. colour television camera 20 and flying spot scanner 30) and mixing 50 the two sets of colour signals to produce a set of composite colour output signals which are used to produce the composite colour picture (e.g. on colour display CRT 58). The foreground signal corresponding to the predetermined colour i.e. blue, is applied to mixer 50 via a limiter 6 which only passes the signal when it is less than one of the other foreground signals i.e. red or green, or more particular a selected factor thereof i.e. between unit and 1À5 times (amplifier 64) the selected other colour component signal (green as shown). The background colour components signals (from detectors 41-43) are applied to mixer 50 via gating circuitry 70 which includes three variable gain amplifiers 71, 73 and 75 whose gains are controlled by a control signal E c  which comprises the difference 74 between the limited 76 blue foreground signal B o  and the same green (or red) amplified foreground signal applied to limiter 60. Signals B o  is made (limiter 76) no larger than the value corresponding to the least brightly illuminated portion of backing 12 so that uniform lighting 16, 17 is not necessary. Preferably B o  is set at the level corresponding to the maximum illumination of the foreground objects 10. When camera 20 scans the background of the foreground the reference signal on line 79 is essentially zero and thus control E c  is maximum and the background signals are transmitted with full normal amplitude to mixer 50. When E c  is zero i.e. when the camera 20 scans the objects 10, the amplifiers 71, 73, 75 act as open switches and mixer 50 receives no input corresponding to the background scene. For intermediate values of E c  corresponding to the camera 20 scanning transparent, partially transparent or moving foreground objects the amplifiers 71, 73, 75 amplify the background scene signals with a gain proportional to E c , and a composite signal comprising both background and foreground signals is produced by mixer 50. The composite signal produced may be recorded on video tape or transmitted instead of being displayed on CRT 58, alternatively display 58 may be photographed on standard intermittently driven motion picture film. Where the foreground and background scenes comprise colour motion picture films each frame may be scanned three times, a colour selector being interposed between the mixer 50 and a black and white display tube and arranged to frame sequentially display the three colour component signals and project the images via a rotating colour filter on to a motion picture film to produce a composite colour picture or three colour separation records. The arrangement of Fig. 1 also permits a motion picture director to observe during photography of the foreground scene 80 the composite picture on the display 58.