Patent GB-1251008-A (GB)
IPC: H04N9/11
Filed: 1968-11-22
Abstract: 1,251,008. Television. COLUMBIA BROADCASTING SYSTEM Inc. 22 Nov., 1968 [24 Nov., 1967], No. 6500/71. Divided out of 1,249,310. Heading H4F. Luminance and chrominance signals produced by a colour television camera are recorded on black and white cinematograph film in respective halves 68 and 70, Fig. 2, of a film frame in a manner similar to that described in Specification 1,131,772. To shorten the number of film frames needed to record a programme of a plurality of pairs of interlaced television fields the luminance and chrominance signals are passed through a one field period delay means 18, Fig. 1 and the delayed and non-delayed luminance signals are alternatively sampled at 27 at a frequency high relative to a line period whilst the spot producing the raster on the printing cathode ray tube 28 is subjected during the luminance display to a castellated line scan, Fig. 2 at said sampling frequency, such that the successive luminance fields are laid down in a dot-interlaced manner, e.g. field 1 on line portions 39 and 42 and field 2 on line portions 41 and 43. The film frame half 70 either has the whole of one frame of chrominance information recorded thereon or the upper and lower halves recorded with the corresponding halves of consecutive frames of chrominance information. Thus a first frame of the film can have dot interlaced luminance information from fields 1 and 2, and chrominance information from field 1 only, whilst the next film frame has luminance information from fields 3 and 4, chrominance information from the lower half of field 3 and the upper half of field 4 in the respective lower and upper halves of film frame portion 70. Pull down of the film from one frame to the next takes place during half a field period every 2¢ field periods, Fig. 1B. To ensure that the delay of the delayed video signal is exactly on field period, a small variable delay 19 is used, servo controlled by the output of a phase detector 22 determining the phase difference between sync. signals derived from the delayed and non-delayed video signals. The chrominance content of the delayed and non-delayed signals is removed by a low pass colour carrier stripper 97 and the two luminance signals passed to the sampling gate 27. The high frequency sampling signal is produced by generator 27a and is also added at 34 to the vertical deflector signal for the tube 28. A raster shift generator 92 adds a constant voltage to the horizontal deflection sawtooth, when the raser on tube 28 is to shift from frame portion 68 to 70. The shifting is controlled by pulses on line 96 (third line Fig. 1B), produced by means 80, 98, 100 and 102 so co-operating that for a first five successive fields the positive pulses of an alternating field switch pulse train (fourth line Fig. 1B) cause the shifts whilst for the next five fields the negative pulses etc. cause the shifts. This gives the position of the raster on tube 28 as shown in the first line of Fig. 1B. The delayed and undelayed chrominance signals are fed to a switch 76 controlled by every fifth field pulse by means of divider 80, such that switch 76 normally passes the undelayed signal for four consecutive fields and then passes the delayed field for the fifth field. The passed chrominances signals are phase modulated on to a ¢Àf c  carrier in 84 as explained in the aforementioned specification and the carrier fed to switch 88. Switch 88 switches over between the chrominance and luminance signals at field rate under the control of the field switch pulse train. The film pull down or frame change pulses (second line Fig. 1B) also cause blanking of the tube 28 by means of line 31 and adder 30. The overall operations may be summarized by the following table:-