Patent GB-1175721-A (GB)
Title: Video Signal Recording and Playback Apparatus
IPC: H04N11/22
Filed: 1967-03-30
Abstract: 1,175,721. Colour television. BELL & HOWELL CO. 30 March, 1967 [30 March, 1966], No. 14539/67. Heading H4F. In a system receiving NTSC type signals the colour difference, luminance and sync. signals are combined to produce colour and sync. signals R + sync., G + sync. and B + sync. which are simultaneously displayed on a show mask tube and converted into line sequential signals for recording on a magnetic video tape. The line sequential signals reproduced from the magnetic tape are arranged to control the electron guns of the shadow mask tube so that each colour signal is displayed during two successive line scans and two consecutively occurring line sequential colour signals are displayed during each line scan. Specifically, the colour signals are applied to the electron beam activating means in the following sequence: only R and B during lines 1, 4, 7-of each first field (interlaced scanning) and lines 3, 6, 9-of each second field, only B and G during lines 2, 5, 8- of each first field and lines 1,4,7-of each second field and only G and R during lines 3, 6, 9- of each first field and lines 2, 5, 8-of each seoond field (i.e. the display sequence is RB, BG, GR, RB-in each first field and BG, GR, RB, BG . . . in each second field). This display sequence of the colour signals is derived by means of a one line scan period delay line together with an arrangement of gates controlled by a sequencing unit comprising a three stage counter or shift-register triggered by the horizontal sync. pulses reproduced from the magnetic tape. The sequencing unit is indexed to a predetermined state once every frame (i.e. every other field), in order to preserve proper colour interlace, by means of a field discriminator which integrates and delays the separated vertical sync. signal, the resulting delayed pulse being applied together with the separated horizontal sync. pulses to anAND gate, thedelay being adjusted so that the delayed pulse coincides with one of the horizontal pulses produced during the vertical blanking interval of one field. The AND gate thus generates an output signal once every frame which is applied to the sequencing unit. In addition to receiving and displaying directly received NTSC signals and converting them into line sequential colour signals for recording on magnetic tape, each colour upon playback being displayed during two consecutive lines with two colours being displayed during each line, the system may also include a video camera and a colour film converter the signals from which may be simultaneously displayed and recorded and the played back recorded signal may be displayed in the same manner as described above. The video camera may comprise a vidicon tube having a horizontally striped colour filter on the face thereof or any other camera which may generate tricolour signals which may be sequentially sampled to produce line sequential signals. Synchronizing signals for controlling the camera and the display tube are derived from standard NTSC signals broadcast from some remote television broadcast station. The operation of the colour film converter is substantially the same as the operation of the video camera and the same vidicon tube may be employed. The specification describes circuits for producing, picking-up, recording and playing-back the accompanying sound signals. By providing a second delay line having a two line scan delay arranged to control another arrangement of gates, three colours may be displayed during each line scan. The colour display tube may comprise a three-gun shadow grid tube having vertical stripes of first, second and third colour response on its face, rather than a shadow mask tube.