Patent GB-1413122-A (GB)
Title: Colour television signal generating apparatus
IPC: H04N9/07
Filed: 1972-12-12
Abstract: 1413122 Colour television NIPPON VICTOR KK 12 Dec 1972 [18 Dec 1971 26 April 1972 30 April 1972 29 May 1972] 57265/72 Heading H4F A colour television camera uses a camera tube having a striped colour filter formed of a repeating sequence of identical groups of stripes, the stripes being at right-angles to the direction of line scan of the camera tube, and each group of stripes including a transparent stripe, a stripe passing light of one primary colour, and at least one stripe passing light of a colour complementary to one of the other primary colours, so that the one primary colour is passed by all stripes. A second camera tube may be included to provide a separate luminance signal (Fig. 1, not shown). A lenticular lens may be included between the filter and the camera tube. In one embodiment, of which Fig. 3 shows the light transmitted when white light is incident on the filter, each group of filter stripes has blue, magenta, and transparent stripes, the blue stripe being of twice the width of the magenta stripe, the magenta and transparent stripes being of equal width. Blue light is thus transmitted through all stripes, red light is transmitted through the magenta and transparent stripes, and green light is transmitted only through the transparent stripes. The resulting output signal includes a low frequency component including the low frequency portions of the blue, red, and green signals which is separated by a low-pass filter 20, Fig. 6. The output signal also includes a component modulated on a carrier whose frequency f1 is determined by the repetition period a of the stripes and which is separated by band-pass filter 21 and demodulated at 22 to provide a combined red and green signal. The output signal from the camera tube is also passed to an adder 25 directly and via a delay 24 having a delay of half a cycle of the carrier of frequency f1. The output of adder 25 includes a low frequency portion derived from the red and blue signals and a carrier at a frequency 2f1 modulated by the green signal, the green signal being derived from demodulator 27, the outputs of lowpass filter 20 and demodulators 22, 27 being passed to a matrix circuit 23 (also Fig. 15, not shown) to derive red, green, and blue signals or colour difference signals. In a second embodiment, of which Fig. 9, shows the light transmitted when white light is incident on the filter, each group of filter stripes again has blue, magenta, and transparent stripes, but the transparent stripe is of twice the width of the magenta stripe, the blue and magenta stripes being of equal width. The output of the camera tube includes similar components to those of the previous embodiment similarly separated by low-pass and band-pass filters (31, 32, Fig. 11, not shown), but also includes a carrier of frequency 2f1 modulated by a red signal, which may be separated by a band-pass filter (33), the carrier being subsequently demodulated (37) and passed via a low-pass filter (38) to the matrix. circuit. A delay line (39, Fig. 12, not shown) and adder (40) similar to delay line 24 and adder 25 of Fig. 5, may be included before the band-pass filter (33) for the carrier at frequency 2f1 to increase the amplitude of the red signal at frequency 2f1. In a third embodiment, of which Fig. 17 shows the light transmitted when white light is incident on the filter, each group of filter stripes has blue, cyan, magenta, and transparent stripes all of the same width, the output signal of the camera tube including a low-frequency component similar to those in the previous embodiments, a carrier at frequency f1 modulated by a red signal and a carrier at frequency 2f1 modulated by a green signal, appropriate band-pass filters being used to separate the components.