Patent GB-1064486-A (GB)
Title: Improvements in or relating to the reproduction of information from a record medium
Inventor: GOLDMARK PETER CARL
IPC: H04N5/84
Filed: 1964-04-29
Abstract: 1,064,486. Television. COLUMBIA BROADCASTING SYSTEM Inc. April 29, 1964, No. 17812/64. Heading H4F. In an arrangement for providing picture and synchronizing information signals from a continuously moving film strip carrying a succession of frames of picture information and a plurality of synchronizing indicia associated with the frames by optically scanning the film with a raster of given periodicity, the synchronizing signals derived from the synchronizing indicia are used to control the periodicity of the raster scan and to maintain the position of the raster scan in registration with the frames of picture information on the film. The synchronizing indicia or markers may comprise a series of regularly spaced opaque and transparent areas across the film strip between each frame, Figs. 2 and 3 (not shown), which when scanned by the light spot of the raster produce a pulse signal of given frequency. As shown, Fig. 1A, the film 12 is scanned by a moving spot of light produced by a CRT or flying spot scanner 32 at a rate of 60 interlaced fields per second for a film speed of 30 frames per second and by means of beam splitter 48, prisms 36 and 38, and a rotating shutter 40 having two slits, Fig. 4 (not shown), each frame on the film is scanned twice with interlaced scansions. A photo-multiplier 58 which detects the light from the scanning light spot that is transmitted through the film thus produces a video signal which is amplified 60, 62, corrected for aperture and gamma distortion 64 and 66, Fig. 1B, and applied to a synchronization mixer 68 in which blanking and synchronization signals from a synchronization generator 70 are added thereto. A tuned amplifier 98, Fig. 1B, is coupled to the video amplifier 62 and is tuned to a frequency equal to that of the signal produced by the light spot sweeping the synchronization markers. The signal from the tuned amplifier 98 is applied to a detector 100 which generates a pulse signal in response thereto which is amplified 102, limited 104 and applied via a transformer 106 as a gating input to a sampler 108. Applied to the sampled input terminal of the sampler 108 is a triangular waveform signal derived from the vertical synchronization pulses from the synchronization generator 70, which trigger the vertical sweep of the light beam in the CRT 32, by means of a multivibrator 110, integrator 112 and transformer 114. Thus the sampler produces an output signal which is indicative of the time during a field sweep of the scanning light spot when the spot is sweeping the synchronization markers on the film, the triangular waveform being arranged to increase to a peak potential from a reference potential and then decrease back to the reference potential during the first on-half portion of a vertical field sweep of the light spot from the CRT 32 and the decrease from the reference potential to a base potential and increase back to the reference potential during the remaining half of the field sweep. The output from the sampler 108 is used as a correction signal which is applied to an amplifier 116 and thence to the synchronization generator 70 and to scanning signal generating circuits 118 to vary the frequency of the vertical pulses generated by generator 70 and to shift the position of the field sweep on the CRT 32 so that it encompasses a frame on the film record 12. The time constants are arranged to be such that the scanning signal generating circuits 118 respond more quickly to the correction signal from the amplifier 116 than does the synchronization generator 70. The vertical pulses from generator 70 are also applied to the shutter motor drive 42 via a square wave generator 120. To ensure that the light beam from the CRT 32 is of constant intensity, a control circuit comprising, a photo diode 52, a source of reference potential 54 representing a standard light intensity, and a comparator 56-are employed. A sound track may be provided on the film record of variable density or variable area. The system may include a control circuit for regulating the peak output signal from the photo-multiplier 58 so that it is relatively uniform for a peak light input by means of a peak detector 90, a comparator 92, a reference source 94 and a voltage regulator 96 which changes the magnitude of the biasing signal applied to the multiplier 58.