Patent GB-765443-A (GB)
Title: High frequency carrier system for electronic colour correction system
IPC: H04N1/60
Filed: 1955-10-03
Abstract: 765,443. Copying-telegraphy; local copying by scanning. TIME, Inc. Oct. 3, 1952 [Oct. 18, 1951], No. 24858/52. Class 40 (3). In a transmitter circuit in which the signals produced by the photo-electric scanning of the subject modulate in amplitude a high-frequency alternating current, the photo-electric device having an anode and cathode is coupled in a direct series connection to an electron current-controlling device having an anode, cathode and control grid so that current flows from anode to cathode of the two devices and no direct current branch connections are included so that the anode-cathode current of the one device flows entirely through the other device and the high-frequency alternating current is applied to the control grid of the second device. The system described employs a black printer with a black separation negative produced as described in Specification 761,535 and with masking colour corrections as described in Specification 712,558. The signal in the cyan channel is modified as a function of the instantanous maximum of the modulation components in the three channels, the yellow signal is masked as a function of the signal in the magenta channel and signal in the magenta channel is masked as a function of the signal in the cyan channel except in yellow areas of the signal when it is masked as a function of the combination of the yellow and cyan signals. The circuit shown may be used for scanning positives or negatives, and with the switch 40 in engagement with contact 41 for the scanning of positives, the output of the photoelectric cell of the scanning unit 38 passes via lead 39 and shielded conductor 53 directly to the cathode 43 of the pentode valve 44, to the suppressor grid 45 of which the carrier frequency is applied from the oscillator 13. With the switch 65a in the position shown, the anode output is fed to the grid 69 of the amplifier valve 70. For scanning negatives, the output from lead 39 passes via switch arm 40 and contact 42 to conductor 111 and via switch arm 68 in engagement with contact 67 to shielded cable 114 and the grid 69 of the valve 70. The arm 119 of the switch 116 is moved into engagement with contact 115, and the carrier frequency is applied via capacitor 120a and contact 67 to the control grid of the valve 70. The output of the valve 70 is fed to a variable compressor 15 comprising non- linear devices, such as the thyrite resistors 91, 92 and resistors 86 ... 90 connected by ganged switches 93, 94. The compressor is biased by an adjustable voltage divider 95 and a directcurrent compression control voltage derived subsequently in the channel and fed via conductor 106 to a resistor 107 and a parallelresonant circuit 108. The output from the compressor 15 is fed to a gain-control device 15a and amplifier 16 connected to the grid of a valve 124, Fig. 5, of an amplifier 18 feeding a H.F. cathode-follower circuit 19 whose output is modulated in a voltage-doubler circuit 20. This output is fed to the grid of a valve 186 connected as a cathode follower and the output is applied to the variable compressor 15. For the masking of the yellow signal the output of the doubler 20<1> in the magenta channel is fed via conductor 125 to the grid 126 of valve 127 also connected as a cathode follower, the output being fed to a circuit to remove any trace of the carrier and then through a tuned circuit to a thyrite network 134, constituting a modulator, as in U.S.A. Specification 2,580,692, which also receives the output of the amplifier 16 and the output of the modulator which comprises the modulated signal from the lead 39 together with a modulation which is a function of the signal in the magenta channel. The cyan signal is modulated as a function of the instantaneous maximum signal in the three channels and this is derived from the cathodes 147, 147<1>, 147<11> of the valves 146, 146<1>, 146<11> and is fed by a conductor 149 and a filter network to a modulator similar to that described for the yellow channel. The masking of the signal in the magenta channel may be effected by the signal in the cyan channel, the output from the doubler 20<11> being passed to the grid 1261 of the valve 1271 whose cathode output is fed to a parallel-resonant circuit 131<1> and to a thyrite modulator similar to 134 in the yellow channel. The grid 1261 of the valve 1271 is also connected to the anode 152 of a multielectrode valve 153, the grids 154 ... 157 and cathode 158 of which are connected by a lead 159 to the output of the doubler 20. In the predominantly yellow portions of the subject the voltage on the grids 154 ... 157 falls and the valve 153 conducts so that the voltage applied to the grid 1261 of the valve 1271 is reduced. The colour-corrected signals are applied to a circuit, Fig. 8, for deviding the black signal and the concomitant adjustment of the colour component signals. The latter are applied to amplifiers, Fig. 6, (not shown), and to amplifiers 24, cathode followers 25 and thence via voltage doublers 26, 26<1>, 26<11> to valves 166, 166<1>, 166<11> connected as cathode followers. The cathodes are connected together, and from a resistor 168 the maximum signal is passed via circuits 169 and 171, lead 172 and limiting device 28 to an amplifier, Fig. 9, controlling the glow lamp to expose the black separation negative. In the yellow channel the filtered instantaneous signal is fed through resistors 174, 175 and a thyrite network 177 which is also connected via lead 179 to the output of the amplifier 23, Fig. 6 (not shown). The output from this amplifier is fed to amplifiers 32, 33, cathode follower circuit 34, rectifier and voltage doubler device 35 to a D.C. amplifier energizing glow lamp 37 of the yellow channel. A diode limiter 184 may be included between the doubler 35 and amplifier 36. To re-introduce or maintain the sharp edges of the original, the output of the photo-electric member 38, Fig. 3, at lead 58 may be differentiated in a circuit 37a comprising capacitor 188 and resistor 189 and fed to an amplifying valve 191 by which it is inverted. The amplified signal, again differentiated in a second circuit 37b comprising capacitor 194 and resistor 195, is fed to the grid 196 of a valve 197 from the anode 198 of which voltage is fed to the grid 201 of a valve 202 in the D.C. amplifier 36. Additionally, the peaking voltage from the connection 199<1> in the magenta channel is applied via connections 203, 204 to the control grid 205 of the valve 206 in the black printer amplifier 29. U.S.A. Specification 2,253,086 also is referred to.