Patent GB-717759-A (GB)
Title: Improvements in flying-spot pull-down film television scanners
Inventor: PEMBERTON MAX ERIC
IPC: H04N3/40
Filed: 1951-10-05
Abstract: 717,759. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Sept. 4, 1952 [Oct. 5, 1951], No. 23270/51. Class 40 (3) In a " flying-spot " scanning arrangement for intermittently moving kinematographic film the area of the "flying-spot" raster is increased beyond that necessary to cover a film picture frame and the duration of the blanking pulses are correspondingly increased. This makes the field blanking period comparable with the "pullthrough " time of the film mechanism so that the latter action is not visible as the reconstituted television picture. The lengthened field and/or line blanking pulses may be modulated in accordance with the average density of the film being scanned to produce a margin which improves the apparent contrast in the reconstituted picture. A design or legend may, also, be produced in the margin. Fig. 1 shows one embodiment in which the enlarged raster ER produced by the "flying-spot" scanner FSST is imaged on to two positions F1, F2 on the film F an apertured mask M the aperture A of which is equal to the normal raster area being interposed in the former optical path and an opaque screen S equal in area to aperture A being interposed in the latter optical path. In operation, signals representative of the film frame which are generated in p.e. cell PE1 and signals representative of the marginal film area generated in cell PE2 are combined after amplification, in a mixer M1 (a delay device D ensuring equality of the response times of amplifiers AMP1, AMP2) the output from which is combined in a second mixer M2 with the normal blanking pulses to blank out that part of the lengthened blanking pulses (from PE2) which includes the line and field retrace periods. To avoid obliquity of the optical path to cell PE2 a "half-silvered" mirror may be included in the optical path to cell PE1 and arranged to direct light on to a mirror which provides a beam normal to film position F2 (Fig. 2 Prov. not shown). Fig. 3 shows an embodiment in which light from the "flying-spot" scanner FSST is passed through the film in one place only (i.e. the optical path including elements L1, apertured mark M, C1, PE1) the signals representative of the film frames which are generated in PE1 being (after amplification) integrated in I and employed to modu'ate the signal output of PE2 which, in this case, is included in an optical path from FSST including elements L2, opaque screen S, C2 and PE2. As in the embodiment of Fig. 1 the signa's after combinations in M1 are combined with the normal blanking signals in M2. By blanking the beam of FSST during the scanning of the extra area (i.e. ER minus UR, Fig. 1) and by reversing the phase of the output of PE2 the mark M and the screen S may be dispensed with. An opaque margin a portion of which is removed to produce a design or legend may be employed to mark the light produced by FSST dunng scanning of the extra area instead of blanking the tube beam (Fig. 1a). In another embodiment (Fig. 5), lengthened line and field blanking pulses produced in pu'se generators PG1 and PG2 respectively are combined in mixer M3 and supp'ied to the "flying-spot" scanner over lead OA so that PE1 supplies signals representative ot the normal film frame surrounded by a black border. These signals, in addition to being fed to mixer M2, are integrated in I and employed to modulate the lengthened blanking pulses fed to modu'ator MD over lead OB and the output from MD is then supplied via a blanking circuit SB in which that of the lengthened blanking pulses which includes the line and field retrace intervals in blanked out by the addition of normal b'anking pulses over lead NS. The output of SB is supplied to mixer M2 via a non-linear amplifier NLA to provide a half-power low relationship between the brightness of the border and the average brightness of the picture. The non-linear amplifier may be dispensed with by allowing the last valve in mixer M2 to limit.