Patent GB-1087091-A (GB)
Title: Improvements relating to colour television signal generators
Inventor: JAMES IVANHOE JOHN PENFOUND
IPC: H04N9/67
Filed: 1963-04-04
Abstract: 1,087,091. Electric analogue calculating. ELECTRIC & MUSICAL INDUSTRIES Ltd. April 3, 1964 [April 4, 1963], No. 13463/63. Heading G4G. [Also in Division H4] In a colour television camera in which three vidicons 4, 5, 6, Fig. 5, produce narrow-band 1/γ 1/γ 1/γ signals E R  , E G  and E B  , and an image orthicon 50 produces a wide-band luminance signal of the form Ey<SP>1/γ</SP> = (0.30 E R  + 0.59   E G  + 0.11 E B )<SP>1/γ</SP> , a non-linear function generator circuit, Figs. 1 and 2 (not shown), forms a signal E v  = E Y <SP>1/γ</SP> - 0.51 (E R <SP>1/γ</SP> - E Y <SP>1/γ</SP> ) -  0.19 (E B <SP>1/γ</SP> - Ey<SP>1/γ</SP> ) from the three signals E R <SP>1/γ</SP> , EG<SP>1/γ</SP> and E B <SP>1/γ</SP> , and the signals E R <SP>1/γ</SP>,   E v  and E B <SP>1/γ</SP> are applied to a linear matrixing circuit (encoder) which derives the colour   difference signals E R <SP>1/γ</SP> - E Y <SP>1/γ</SP> and E B <SP>1/γ</SP> -   E Y <SP>1/γ</SP> for transmission with the luminance signal E Y <SP>1/γ</SP>. The circuit of Figs. 1 and 2 (not shown), which operates on the same basis as that described in Specification 1,025,924 includes four groups of resistors each group comprising a linear function generator arranged to produce a linear combination of the signals E R <SP>1/γ</SP> , E G <SP>1/γ</SP> and E B <SP>1/γ</SP> which is an approximation of the function E v . The values of the resistors are so chosen that for each set of input signals one linear approximation i.e. the maximum value, will be nearer to the correct value than the others. This maximum value is selected by connecting the outputs of the resistor groups to the anodes of four diodes which have a common cathode impedance.  In a colour television receiver which receives colour difference components of the form E R <SP>1/γ</SP> - Ey<SP>1/γ</SP> and E B <SP>1/γ</SP> - E Y <SP>1/γ</SP> the output of the linear matrixing circuits used to produce a green component signal will produce an incorrect green signal E v  which exceeds the correct green signal E G <SP>1/γ</SP> by an amount given   by 1-7 (E Y <SP>1/γ</SP> - E Y <SP>1</SP>), E Y <SP>1</SP> being the N.T.S.C. type luminance signal which equals 0.30 E R <SP>1/γ</SP> + 0À59 E G <SP>1/γ</SP> + 0.11 E B <SP>1/γ</SP> . The correct signal E G <SP>1/γ</SP> may be derived from the signal   E R <SP>1/γ</SP> , E v  and E B <SP>1/γ</SP> by means of a non-linear function generating circuit, Figs. 3 and 4 (not shown) which is similar to the circuit of Figs. 1 and 2 (not shown), but in which the diodes are replaced by transistors arranged to select the minimum output from the linear function generators. In a further embodiment a four-tube colour television camera 40, Fig. 6, produces a wideband luminance signal E Y <SP>1/γ</SP> and three narrowband signals E R <SP>1/γ</SP>, E Y <SP>1/γ</SP> and E B <SP>1/γ</SP> . These three signals are applied to a linear function generator 41- which generates E Y  and a non- linear function generator 42 which generates 1/γ an approximation to the signal E G  . If the switch 44 is in the position indicated the colour difference signal outputs of encoder 43 will be   of the form E R <SP>1/γ</SP> - E Y <SP>1/γ</SP> and E B <SP>1/γ</SP> - E Y <SP>1/γ</SP>, and if the switch 44 is in the other position the chrominance outputs of encoder 43 will be of 1/γ 1/γ the form E R  - E Y <SP>1</SP> and E B  - E Y <SP>1</SP>. The encoder may be switched to provide an N.T.S.C. or " SECAM " (Registered Trade Mark) type chrominanee signal. The wide-band luminance signal is transmitted through the encoder unaltered. The function generating circuits may be arranged to generate luminance difference signals E Y <SP>1/γ</SP> - E Y <SP>1</SP> as a function of E R <SP>1/γ</SP>,   E G <SP>1/γ</SP> and E B <SP>1/γ</SP> and also signals of the form E v  - E G <SP>1/γ</SP> . The Specification states that if the low-frequency components are subtracted from   signal E Y <SP>1/γ</SP> , a modified luminance signal is produced which is E Y <SP>1</SP> for low frequencies and E Y <SP>1/γ</SP> for higher frequencies.