Patent GB-1251497-A (GB)
IPC: H04N9/82
Filed: 1968-09-30
Abstract: 1,251,497. Colour television. INTERNATIONAL BUSINESS MACHINES CORP. 30 Sept., 1968 [14 Nov., 1967], No. 46234/68. Heading H4F. In an apparatus for recording colour video signals, separate images of the three colour components red (R), blue (B), and green (G) and the luminance (L) are recorded sequentially on oblique tracks 39 on a tape 12 as shown in Fig. 3. The tape is moved incrementally by a motor-driven capstan 18 and pinch wheel 19 around a fixed drum 10, the tape being wound in a helical fashion around this drum (see Fig. 1). A rotatable disc 28 within the drum has two vertically-spaced tape heads 30 and 32 at its perimeter which contact tape 12 through a slit in drum 10. Disc 28 is rotated by a motor 70, the video signal from the colour camera 42 being switched from head to head on alternate revolutions by means of AND gates 36 and 38 and a bi-stable multivibrator 34, controlled by a photoelectric cell 64 which generates a signal in response to a reflecting marker 66 attached to disc 28. This signal is also compared with a signal similarly generated by the rotations of a colour disc 44 such that disc 44 rotates at half the speed of disc 28, the tape 12 being stepped on by the capstan 18 on completion of each rotation of the colour disc 44. As shown in Fig. 2 the disc 44 comprises four sectors containing filters for the red, blue, green and luminance components. A sync. generator 52 provides marker signals 79, Fig. 3, on tape 12 via a recording head 60, and also synchronizes the electron beam scanning of the camera. Fig. 3 shows apparatus for playing back the recorded video signals to a tri-colour display cathode-ray tube 102, the playback apparatus being similar to the recording apparatus except that during playback the two heads 30 and 32 are operative simultaneously. The resultant video signal outputs from the demodulators 86, 88 coupled to the heads 30, 32 are applied to respective pairs of AND gates 90, 92 and 94, 96 coupled as shown to three OR gates 108, 110, 112 whose outputs are applied to the R, B and by guns 114, 118, 116 of the tube 102. During a first half rotation of the disc 28 (i.e. first field period), bi-stables 104 and 106 are set by the trigger pulse output from the photo-cell 64 responsive to the reflecting marker 66 thereby enabling the AND gates 90 and 94 to apply the R and G signals simultaneously to the R and G guns 114, 116 and during the next half rotation of disc 28 (second field period) the bi-stables 104, 106 are re-set by a trigger pulse output from a photo-cell 122 responsive to an additional reflective marker spaced 180 degrees from the marker 66 thereby enabling the AND gates 92 and 94 to apply the B signal to the B gun 118 and to simultaneously apply the luminance (L) signal to all three guns 114, 116, 118. The above operation is repeated during the next rotation of disc 28 (fields three and four) and the tape 12 is then stepped on by the capstan 18 for playback from the next pair of tracks. Alternate fields on the display tube 102 may be interlaced in the usual manner. Fig. 4 shows a modified form of colour disc comprising twelve sectors, every fourth sector comprising a filter that passes a combination of colours, e.g. R and B, R and G, B and G, in lieu of the monochrome component.