GB1033413A - Improvements in or relating to colour television systems - Google Patents

Abstract

1,033,413. Colour television. MARCONI CO. Ltd. May 10, 1963 [July 24, 1962], No. 28435/62. Heading H4F. In a colour television transmitter a luminance signal is derived which is composed of two portions occupying adjacent frequency bands, one, occupying the lower frequency band, representing the combination of individually gamma-corrected primary colour components (i.e. it is a signal of the form Y<SP>1</SP>=0À30R<SP>1</SP>/γ + 0À59G<SP>1</SP>/γ + 0À11B<SP>1</SP>/γ) and the other, occupying the higher frequency band, representing the gamma-corrected combination of the primary colour components (i.e. it is a signal of the form Y<SP>1</SP>/γ = (0À30R + 0À59G + 0À11B)<SP>1</SP>/γ). Fig. 1 shows a first embodiment in which R, Y and B linear signals from a camera 1, which utilizes image orthicon camera tubes, are applied through lowpass filters 2, 3 and 4 to a matrix 5 for deriving a G signal. The R, G and B signals are then individually gamma-corrected in circuits 6, 7 and 8. The resultant signals pass to a matrix 9 for deriving I<SP>1</SP>, Q<SP>1</SP> and Y<SP>1</SP> signals in accordance with the N.T.S.C. signal standards. The passbands of filters 2, 3 and 4 correspond to the frequency band occupied by the I<SP>1</SP> signal. In accordance with the invention, the luminance signal Y is also applied to a gamma-correction circuit 10 to derive a signal Y<SP>1</SP>/# and this signal is then passed through a high-pass filter 11 whose pass band is complementary to that of filters 2, 3 and 4 so that the combined pass-band corresponds to the frequency band assigned to the finally transmitted luminance signal. The signal from filter 11 is combined withsignal Y<SP>1</SP> from matrix 9 after first passing through a delay line having a delay equal to that experienced by signals I<SP>1</SP>, Q<SP>1</SP> and Y<SP>1</SP>. In a second embodiment, Fig. 2 (not shown), the camera produces linear R, G and B signals directly and a Y signal is formed in a matrix from appropriate combinations of R, G and B. A third embodiment, Fig. 3 (not shown), employs a camera having vidicon camera tubes which produce signals initially of the form E<SP>1</SP>/γ. The signals are applied through low-pass filters 2, 3 and 4 as in Fig. 1, but before the G signal may be derived in matrix 5 they are restored to linear form in networks 14, 15 and 16. The G signal is then gamma-corrected in a circuit 7 and applied to matrix 9 together with the non-linear signals from filters 2 and 4. The luminance signal being initially in the necessary non-linear form Y<SP>1</SP>/γ is merely restricted to the appropriate highfrequency band in filter 11 and then passed through delay line 12 for combination with the luminance signal Y<SP>1</SP> from matrix 9. A fourth embodiment, Fig. 4 (not shown), is similar in that it utilizes vidicon camera tubes, but the camera signals in this case comprise R, G and B. After low-pass filtering the signals are used directly in matrix 9 and are also converted to linear form and then combined to form a luminance signal. This is then gamma corrected to Y<SP>1</SP>/γ and combined with luminance signal Y<SP>1</SP> from matrix 9 after restriction to the complementary high frequency band. If desired, low-pass filters 2, 3 and 4 may be located after matrix 9. The Q<SP>1</SP> signal may be restricted in matrix 9 to a band which is narrower than that of the I<SP>1</SP> signal. Reference is made (without giving details) to the application of the invention to the SECAM and SEFAM systems.