Patent GB-1537303-A (GB)
Title: Method of and apparatus for manufacturing a video record
IPC: G11B7/24097
Filed: 1976-03-19
Abstract: 1537303 Television PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 19 March 1976 [24 March 1975 8 Oct 1975] 11148/76 Heading H4F In a stop-motion television picture display system in which two interlaced fields recording in a single-turn (or multi-turn) circular (e.g. spiral) track of a video record disc which is read optically or magnetically are repeatedly read and displayed, to prevent the occurrence of troublesome flicker, which results due to movement taking place in the televised scene between the two field periods, the video information supplied to the video recorder is modified in such a manner that picture quality during continuous (motion) display is not affected. The video information, e.g. from a camera, is divided into discrete groups which each comprise two field periods, in which groups the video information of the two field periods themselves or of preceding field periods after suitable delay of one or more field periods as combined in desired ways before being recorded. Picture synchronizing signals, in addition to standard synchronizing signals, are also recorded for locating the starting points of the discrete groups of two associated field periods. In one embodiment, Fig. 3, the received video signal A from a source 21 is converted into a modified signal F for recording on disc recorder 20. The signals A and F and at other points in the circuit for the two field periods of a discrete group recorded for stop-motion display without flicker are represented in the form of instantaneous information samples i with a field number superscrip "N" and a line number subscript "n". The arrangement of Fig. 3 includes one line period T H  delays 25 and 26, a delay 33 of one field period Tv minus one half of a line period, attenuators 27, 29, 34, 37 and 38 having multiplying factors of -¢, -¢, ¢, p and q, adding stages 28, 32 and 35, and switching devices 30 and 36 operated at the field frequency by the output of switching signal generator 31 whose output frequency is halved 39 and supplied to the recorder 20 to form the picture synchronizing signals which may be recorded as a mark on the video disc or by modifying each field sync. signal recorded. The components 25-29, 35 and 37 comprise a vertical aperture correction circuit, although further embodiments described do not include such a circuit. As described with reference to Figs. 2 and 4 (not shown), the flicker phenomenon is removed when p=¢ and q=1 for shift in the field scanning direction and also in the lines scanning direction (described with reference to Fig. 5, not shown). Instead of delay device having a delay of substantially a field period a frame period delay device may be used. To record a colour television signal of NTSC or PAL form only the luminance signal Y, Fig. 12, is modified in a device 71 having components 25-39 of Fig. 3 or preferably of Fig. 6 (not shown), since in this latter embodiment the two fields of each group include whole aperture correction signals. The colour difference signals R-Y and B-Y are fed via delays of T H  and Tv +3/2 T H  and field operated switches 74 and 77 to encoder 78 which provides a standard NTSC or PAL signal with modified luminance in discrete groups of two field periods whilst the colour information remains unchanged and is the same in the two field periods of each discrete group. Delays 72 and 75 may be removed and delays 73 and 76 changed to Tv + ¢ T H  delays. In a further embodiment the colour signal may be filtered, 80, Fig. 13, into luminance Y and chroma signal Ch, in which case an inverter 86 is required for NTSC signals and a phase changer 87 for PAL signals which includes a burst gate 89, a frequency doubler 90, a multiplier 88, a low pass filter 91 and a -90 degrees phase shifter 92.