Patent GB-1086542-A (GB)
Title: Improvements in or relating to circuit arrangements for producing a colour television signal or signals
IPC: H04N9/69
Filed: 1966-04-20
Abstract: 1,086,542. Colour television. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. April 20, 1966 [April 22, 1965; Sept. 17, 1965], No. 17322/66. Heading H4F. Colour signals E R , E G  and E B  from camera tubes 1, 2 and 3 are combined in matrix 6 to form a luminance signal E y * = 0À59 E G  + 0À30 E R  + 0À11 E B , which is of low definition (and hence low bandwidth) due to erroneous scanning registration, defocused scanning beams or defocused optical images, the signal being subtracted in circuit 7 from a high definition luminance signal E y  = 0À59 E G  + 0À30 E R  + 0À11 E B  obtained from a separate luminance camera tube 4 to obtain a difference signal E y  - E y *, an adjustable proportion #of which is derived via potentiometer 22. This difference signal is then combined in adders 8, 9 and 10 with the original colour signals to produce modified signals E<SP>1</SP> R , E<SP>1</SP> G  and E<SP>1</SP> B . The modified signals are gamma corrected in circuits 11, 12 and 13, and finally processed in matrix circuit 14 into E<SP>1</SP> 1 , E<SP>1</SP> Q  and E<SP>1</SP>y in accordance with the N.T.S.C. standards. These final signals are suitable for transmission to a conventional N.T.S.C. receiver, the E<SP>1</SP> 1  and E<SP>1</SP> Q  signals being limited in bandwidth in filters 15 and 16 and modulated in quadrature phase relationship onto a carrier signal in circuit 17 to produce a chrominance signal E<SP>1</SP> c  in the customary manner. It is demonstrated that the brightness of the picture reproduced in the receiver is determined by E y  + (# - 1) (E y  - E y *). If # is chosen to be zero (thereby simulating the action of a camera comprising only colour tubes 1, 2 and 3), the reproduced brightness is proportional to E y * and the detail is poor due to the erroneous scanning registration and other factors. However, if in accordance with the invention, # is chosen to equal 1 the reproduced brightness is proportional to E y  and the picture is free from the errors due to camera tubes 1, 2 and 3. Furthermore, if # is made greater than 1 (the preferred value lies between 1 and 2À5), the sharpness of the reproduced picture becomes even better than that inherent in the signal E y . In a first modification, Fig. 6 (not shown), it is arranged that the low-frequency components of the signal E y  - E y * are supplied to adders 8, 9 and 10 with a lower value of # than the remaining signal components. This is done by deriving a first output from circuit 7 directly via a potentiometer (25) and a second output via a high-pass filter (24) and a second potentiometer (25). The amplitude of # for the low-frequency components is set by potentiometers (23) and the increase of the high frequencies over the low frequencies is set by potentiometers (25). In a second modification, Fig. 7 (not shown), colour-difference signals of the form E R  - E y * are formed from the original colour signals in a matrix (18) and then the signal E y  from the luminance camera tube is added to the colour difference signal to produce signals E R <SP>1</SP>, E<SP>1</SP> G  and E<SP>1</SP> B . In this arrangement # is inherently restricted in value to 1.