| 摘要 |
876,666. Colour television. ELECTRIC & MUSICAL INDUSTRIES Ltd. Dec. 11, 1957 [Dec. 14, 1956], No. 38164/56. Class 40(3) Relates to an arrangement for modifying a colour ratio subcarrier signal of frequency w of the form The original signal, Fig. 2a, varies in amplitude in accordance with hue such that the vectors 1, 2 and 3 representing respectively saturated red, blue and green are in the ratio 1:3:0À565, whereas the corresponding vectors 4, 5 and 6 of the modified signal, Fig. 2b are of equal amplitude. In the circuit for carrying out the invention, Fig. 1, the original signal E c is applied to an amplifier 7 the gain of which is varied by a control signal in accordance with the hue in such manner that the amplitude variation is removed and the desired modified signal is established. The control signal is obtained by applying the original signal to a limiter 8 to obtain a signal varying only in phase in accordance with hue and then sampling the signal in gate stages 9, 10 and 11 at angles of 270 degrees, 30 degrees and 150 degrees respectively. The gate outputs represent respectively -0À87B+0À87G,0À87R-0À87G,-0À87R+0À87B, where R, G and B represent the primary colour co-ordinates. A matrix 12 derives signals representing R, B and G and these are then applied through amplifiers 13, 14 and 15 having gains of 1, 0À33 and 1À77 respectively. The final signals are combined in adder 16 and form the control signal. In an alternative way of carrying out the invention there is added to the original signal after its passage through a limiter, a biasing oscillation 20, Fig. 2c, of frequency w, the amplitude and phase of which are selected so that the resultant vectors 21, 22, 23 for red, blue and green are in the approximate ratio 1:0:33:1À77. A simple amplitude detector may then be employed to derive the control signal. In practice this arrangement permits only an approximate modification. An improvement may be obtained by repeating the process in a second identical arrangement. The invention may be employed in receivers as described in Specifications 871,367 and 877,766. Where it is desired to convert an accompanying luminance signal E Y into an equi-energy signal E E this may be done as described in Specification 6575/57. Specifications 863,604 and 864,452 also are referred to. |
