Patent GB-796059-A (GB)
Title: Image-reproducing system for a color-television receiver
IPC: H04N9/26
Filed: 1955-03-23
Abstract: 796,059. Television. HAZELTINE CORPORATION. March 23, 1955 [April 19, 1954], No. 8471/55. Addition to 784,055. Class 40 (3). In a colour television receiver employing a single gun-type of picture reproducing tube having a screen consisting of repeating groups of R (red), G (green), B (blue), G (green) colour producing phosphors and a co-operating colour switching grid a received N.T. S.C. type of colour signal is modified for application to such tube by firstly deriving a corrected luminance signal which is applied to the cathode of the tube and secondly, deriving a corrected chrominance signal which is applied to the control grid electrode of the tube. The corrected luminance signal is derived from the Y luminance signal of the received N.T.S.C. signal by combining with the latter in filter 47 the 0-0.6 Mc/s. components of a signal M-Y which is developed by synchronous detection, at the correct phase, of the received sub-carrier wave signal in detector 50 the output of filter 47 which is supplied to the cathode of the picture-reproducing tube 29 via the D.C. restorer 48, then comprising the signal M=<SP>1</SP>/ 3  (G+R+B) which is the required luminence signal. To produce the corrected chrominance signal the R-B component of the received N.T.S.C. chrominance sub-carrier is first derived by detecting the latter at 209 degrees phase angle (the B-Y component being considered 0 degree reference phase) in detector 37 and the 0-0.6 Mc/s. components caused to modulate in 38 the locally produced colour reference sub-carrier wave, the phase of the latter curve D (Fig. 2), being adjusted in 39 to be the same as that of the colour switching wave, curve A (Fig. 2), supplied from the generator 21 via amplifier 35 to the colour switching grid 33. The received chrominance sub-carrier is also detected at 140 degrees phase angle in detector 43 to derive the G-¢B-¢R component and the 0-0.6 Mc/s. components of the latter caused to modulate in 44 a wave having twice the frequency of the colour reference subcarrier and a phase, adjusted by the second harmonic amplifier 42, relative to that of the wave supplied to modulator 38 as shown in curve E (Fig. 2). The 6.6-7.8 Mc/s. components of the output of 44 are then combined with the 3.0-4.2 Mc/s. components of the output of modulator 38 in adder 52 and the output of the latter supplied to the modulating grid of tube 29. The Specification considers the sequential production of colours by a single gun tube of the type shown at 29 and shows that correct colour rendition may be obtained from a N.T.S.C. type of signal by modulating the cathode of the tube by the corrected luminance signal and modulating the grid by fundamental and second harmonic sub-carrier wave signals modulated respectively by the R-B and G-¢B-¢R colour components as described above. If a lower degree of colour accuracy is sufficient the received Y luminance signal may be applied directly to the tube cathode without correction. In a second embodiment (Fig. 4, not shown), the R-B axis of the received chrominance sub-carrier is selected (instead of detecting the R-B components as in Fig. 1) and the 3.0-4.2 Mc/s. components thereof supplied to adder 52, the remainder of the circuitry being identical with that shown in Fig. 1. Specification 772,791 is referred to.