Patent GB-1399433-A (GB)
Title: Apparatus for recording and reproducing picture signals and a medium for carrying said picture signals
IPC: H04N5/84
Filed: 1973-03-16
Abstract: 1399433 Video recording NIHON DENSHI KK 16 March 1973 [18 March 1972 (2)] 12886/73 Heading H4F To record two video signals, e.g. the chrominance signals (R-Y) and (B-Y) on to a single frame of a recording medium, e.g. a film strip, by means of a raster scanning modulated energy beam, the two signals have their D.C. levels shifted whereby they occupy respective abutting ranges and the shifted signals are alternately sampled at a frequency higher than the horizontal line rate to produce a recording signal containing alternate samples of the two signals. At least one standard signal, e.g. the level where the two ranges meet on the two D.C. shifting values, is added to the recording signal at the initial and/or terminal part of each horizontal line scan to produce a final recording signal which is used to modulate said scanning energy beam. In the embodiment of Figs. 1, 2(a), 2(b) and 3, the luminance Y and chrominance V R , V B  signals are recorded by respective modulated raster scanning electron beams 8a, 8b on laterally adjacent frames 40a, 41a of a cinefilm 4. Sound tracks 43a, 43b and sync marks 42a are also carried by the film. The chrominance signals, produced by decoder 21 are fed to respective clamp and gate circuits 27a, 27b and 31a, 31b where intervals at the end of each line and the blanking intervals H BL  are first clamped to zero (using clamping signal Fig. 3(f) and the chrominance signal so biased by respective voltages V R  (=7À5V). and V B  (=2À5V), that the end intervals and the intervals H BL  for the the signals V R  and V B  are now at 7À5V and 2À5V respectively and the possible range of V B  is 0 to 5À0V and of V R  is 5À0 to 10À0V. The biased signals are sequentially sampled in circuit 33 at 1MHz to give signal (c) and the signal during the intervals H BL  is removed to give a constant voltage (= 5À0V) (the ends of each line are still at 7À5V or 2À5V). The first half of the intervals H BL  is further reduced to zero by a blanking signal (i) to give the final chrominance signal (e) for recording. The chrominance frame Fig. 2a has a constant left hand edge 44 representing V c  or 5À0. The bands 45, 46 then follow due to the alternately sampled V R  and V B  signals followed by bands 47, 48 representing 2À5V and 7À5V respectively. Gates 31a, 31b may be dispersed with, whereby bands 47, 48 are removed. The value V c  plus and minus the known valves of the biasing then give the values 7À5V and 2À5V. Gate 35 may be dispensed with, whereby area 44 is removed and V c  is obtained by averaging the bands 47, 48. For reproduction of the signals recorded on the film of Fig. 2b, the embodiment of Fig. 4 is used wherein raster scanning light beams from a CRT 52 synchronized by the sync marks 42 on the film via light source/detector system 57/ 59 scan the luminance and chrominance frames to corresponding Y and chrominance signals from detectors 56a, 56b. A clamp circuit 65 and anti-parallel biased diodes 67, 68 fed with the signal V c  = 5À0V as a reference and with a first clamp pulse Fig. 5(d) also at V c  divides the signal Fig. 3(e) into that part above 5À0V, i.e. V R , which part passes via diode 67 for envelope detection at 71(b) and that part below 5À0V, i.s. V B , which part passes via diode 68 for envelope detection at 71b. The detected V R  signal (Fig. 5(b) has its binary reduced to zero at 72a and 76a to give the output signal V R , for combination at encoder 63 with the similarly produced signal V B  and the luminance signal Y.