Patent GB-714155-A (GB)
Title: Improvements relating to colour television apparatus
Inventor: JAMES IVANHOE JOHN PENFOUND
IPC: H04N9/07
Filed: 1950-12-23
Abstract: 714,155. Colour television. ELECTRIC & MUSICAL INDUSTRIES, Ltd. Dec. 10, 1951 [Dec. 23, 1950], No. 31317/50. Class 40 (3). [Also in Group XL(c)] Colour component signals are generated by projecting the image on to the target 6 of a signal generating tube 1, Fig. 1, through a red, blue and green striped filter 7, which is scanned transversely of the stripes, whilst red and blue light sources 15, 16 and 17, 18 are arranged to illuminate the target continuously with the correct intensities of light to cause the three colour signals to occupy separated amplitude ranges each, for example, of 1 volt as indicated in Fig. 2. After amplification and D.C. re-insertion the signals are applied to a circuit 14 in which the red blue and green signals are separated into individual channels 25, 27 and 31 respectively. Separation is effected by three diodes 19, 20, 21 which are biased as indicated so as to pass signals only in excess of 2, 1 and 0 volts respectively. Accordingly, diode 19 passes only the red signals which appear in channel 25. Diode 20 passes both red and blue signals, these being applied to the channel through resistor 26 and to the grid of valve 28. The anode of the valve feeds the channel through condenser 30 and the valve is biased by battery 29 so as to become conductive only for signals in excess of 2 volts. By this means the blue signals appear normally in channel 27, but the red signals are displaced below the 1 volt level by the reversed signal through valve 28 and are removed subsequently by limitation. In a similar manner diode 21 and valve 33 having a bias 34 of 1 volt allow the green signals to pass normally into channel 31, whilst the red and blue signals are displaced below the 0 volt level where they are removed by limitation. If desired, diode 21 may be dispensed with. In a modification,. the green signals may occupy the middle range of the signal output from the signal generating tube. The signals in channels 25, 27 and 31 may be employed to produce the colour fields simultaneously. Alternatively they may be employed to produce signals of the frame-, line- or dot-sequential type. In an arrangement for producing signals of the fieldsequential type, Fig. 3 (not shown), each channel is associated with a cathode-ray storage tube, the signals being stored during the two field periods not allocated to the colour and being regenerated and added to the normal channel signals during the field period allocated to the colour. This arrangement increases the signal-to-noise ratio since the signals are integrated over three field periods. The arrangement illustrated in Fig. 1 may be arranged to generate low definition colour signal by reducing the number of stripes in the colour mosaic and may be associated with a second signal generating tube producing high definition black and white signal as described with reference to Fig. 5 of Specification 714,154. The invention may also be applied to apparatus for the generation of signals from kinematograph film as described in Specification 475,032 by placing the striped filter between the film gate and photo-electric cell.