Patent GB-434274-A (GB)
Title: Method of and arrangement for the television transmission of kinematograph films
IPC: H04N5/202
Filed: 1934-01-27
Abstract: 434,274. Television; valve amplifying circuits. RADIOAKT.-GES. D. S. LOEWE, 10, Wiesenweg, Steglitz, Berlin. Jan. 27, 1934, No. 2839. Convention date, Jan. 31, 1933. [Classes 40 (iii) and 40 (v)] A system for the transmission of kinema films in corporates means for intensifying the contrast in those parts of the film wherein the details of the greater portion of the picture are insufficiently contrasted to result in satisfactory reproduction ; i.e. the details are included in a limited range of the tone scale. For example, where the pictures mainly comprise black subjects with a dark grey foreground the contrast in the dark zone of the tone scale is amplified with consequent disregard of the reproduction of the correct relative contrast of the details occurring in the light portion of the pictures. The correction may be applied to the black or white zones of the tone scale, or the contrast in the middle zone (grey) portion of the tone scale may be amplified. When "black" and " white " corrections are required these may be effected simultaneously or they may be applied alternately to successive pictures of the series requiring these corrections. The control of the correcting arrangement may be effected manually, automatically or semi-automatically. In the latter case a tape is punched during visual examination of the film and the position of the perforation controls the application of the appropriate correction. In the arrangement shown in Fig. 7 the picture potentials are applied to a valve 1 which operates on the upper bend, straight portion or, lower bend, of its characteristic according to the position of a threeposition switch which in the position 5 biasses the valve to provide a " black " correctiona " white " correction being obtained when the switch is in the position 7. In the arrangement of Fig. 8, which avoids positive bias on the grids of the valves 1, 2, the movement of the switch 8 to the dotted line position introduces a "white correction, whilst the movement of switch 7 to its dotted line position biasses the valve 1 to effect a " white " correction which is changed by the valve 2 to a " black " correction. When the switches 7, 8 are simultaneously in the dotted line positions, a correction is effected in the grey zone of the tone scale. Automatic operation may be effected by feeding the amplified picture signals to a valve which passes current when a predetermined potential has been exceeded and which charge a condenser connected to a relay so that with the absence or rare occurrence of black signals the condenser is continuously charged to a potential sufficient to operate a relay which controls the correcting valve to provide a " white " correction. The picture signals may also be applied to a second valve biassed so that it passes current only when a predetermined potential is not exceeded and if few white signals are present, a " black " correction is effected. In a further modification, Fig. 9, the correction is effected by a hot-diode 12 which, for a " white " correction, is placed after the final valve 9 of the amplifier. The potential at which the diode 12 is effective to control the output from the valve 9 is regulated by a variable potentiometer resistance 17 which is set in accordance with the range over which amplification of contrast is required. For a "black" correction the diode 12 is placed in front of the valve 9.