Patent GB-1337081-A (GB)
Title: Apparatus for reproducing video information
IPC: H04N3/38
Filed: 1971-05-13
Abstract: 1337081 Television MITSUBISHI DENK1 KK 13 May 1971 [13 May 1970] 14716/7I Heading H4F Relates to a flying spot scanner arrangement for scanning a continuously moving record media e.g. optical film 10, Fig. 1, to produce a television-type video signal having a desired number (e.g. 50) of fields per second regardless of the moving velocity of the film, the film having a synchronizing mark 26, Fig. 2, in each space 24 between the information carrying areas 22. This invention enables slow, still and fast motion reproduction to be effected, the video signal always having the same number of fields per second. The vertical deflection (plates 36) of the CRT 30 is controlled by a deflection circuit 40 which receives at input 44 pulses generated by circuit 62 in response to each sync. signal corresponding to a sync. mark 26 on the film separated from the video signal by circuit 60 (sync. marks 26 each comprise a regularly spaced bar pattern which produces a given frequency when horizontally scanned). Deflection circuit 40 is shown in Fig. 3 and includes a frequency discriminating circuit 70 which generates a voltage Ef which is proportional to the repeating frequency f of the sync. mark pulses applied to input 44. Ef is proportional to the relative velocity between the film and the flying light spot in the direction of film movement. This voltage Ef is then compared in comparator 76 with a base voltage Es whose value is determined so that the video signal has the desired number of fields per second. Actually Es is determined so as to be equal to the voltage Ef when the scanning light spot is not deflected in the vertical direction and the film is so moved that a video signal having the desired number of fields per second is produced (each field corresponding to an information carrying area on the film). The resulting difference signal E1 is fed via switches 80 and 90 (see later), amplifier 104 which has a time contact determined by resistor 100 and capacitor 108, and amplifier 106 to control the vertical deflection of the scanning light spot produced by the CRT 30 with the result that the difference signal E1 tends towards zero when the vertical velocity of the light spot is such that the relative velocity between the film and light spot produces the desired video signal field rate. Switches 80 and 90 are included in the circuit to produce flyback of the vertical deflection of the light spot, for a distance corresponding to one or more film frames D, whenever the spot is deflected too far in either direction (i.e. out of the focusing range of lens 46, Fig. 1, or the electron beam is reflected past the edge of faceplate 32, Fig. 1). Switch 80, which normally connects input 82 to output 88, is associated with a returning device 150 in which the deflection output voltage Era is compared with an upper limit value Eu and when it is higher an output is fed via AND gate 156 (when a sync. pulse is present at input 44) to a pulse generator 158 which actuates switch 80 to cause the voltage from a returning voltage source 160 to be fed to output 88. This voltage causes flyback. Similarly a returning device 170 operates to produce flyback by comparing voltage Era with a low limit value El with resulting operation of switch 90. The record medium may comprise a thermoplastic record media. The arrangement may be modified to operate with a record media which has been recorded with any number, for example only one half or one third the number, of information areas per second as compared to the number of television fields per second to be generated.