Patent GB-1193714-A (GB)
Title: Colour Video Signal Generating Apparatus
IPC: H04N9/07
Filed: 1967-07-25
Abstract: 1,193,714. Colour television cameras. SONY CORP. 27 July, 1967 [3 Aug. 1966; 19 Sept., 1966], No. 34516/67. Heading H4F. [Also in Divisions G2 and H1] An image of an object O, Fig. 7, is formed on the target 4 of a single pick-up tube 7 (which may be a vidicon) through an optical path which includes a filter 8<SP>1</SP> for selecting component colours and an element 9<SP>1</SP> which includes portions 9a which function as lenses 4 and intervening flat portions which do not function as lenses. The arrangement is such that portions 9a cause the image light to be broken up into component colours, whereas the intervening portions allow a panchromatic image of the object to be formed. The tube may thus be used to provide simultaneously component colour signals and a luminance signal. In Fig. 7 the portions 9a are cylindrical elements with the axes extending at right-angles to the line scan direction, although reference is made to the use of an element including spherical lens portions, Fig. 20 (not shown). Filter 8<SP>1</SP> has an overall green transmission and red and blue transmissions with sinusoidal distributions at two different periodicitics, Fig. 6 (not shown). The principal lens 10 of the system focuses the object O on the tube target 4, whilst the lens portions 9a focus the filter 81 on the target with the image formed by each portion extending over a distance corresponding to two lens portions and two intervening portions. Adjacent images thus overlap. The resulting image pattern takes the form shown in Fig. 8, where, in addition to the panchromatic image (not illustrated) due to the flat portions 9b, there is produced a uniform green image 15b and red and blue images 15R, 15B with sinusoidal intensity distributions along the line scan direction. Fig. 8 represents the maxima of the distributions which occur at different periodicitics. Upon scanning the pick-up tube, a complex video signal is generated as shown in Fig. 10, where f 2  is the product of the line scan frequency and the number of lens portions 9a in the line scan direction. Component 18Y comprises a luminance signal and components 18R and 18B comprise carrier signals modulated by red and blue information. In addition there is a component 18Y<SP>1</SP> due to the green image together with the D.C. low frequency components of the red and blue images. Filters 19R and 19B, Fig. 7, select the carrier signals for application to detectors 20R and 20B to obtain the red and blue signals, whilst filter 19Y<SP>1</SP> selects the signal 18Y<SP>1</SP> from which the detected red and blue signals are subtracted in circuit 23 to derive a green signal. Finally a filter 19Y extending over the band -1¥ f 2  selects the signal component l9Y to which the signal 18Y<SP>1</SP> from filter 19Y<SP>1</SP> and the red and blue signals from detector 20R and 20B are added in circuit 22 to obtain a luminance signal. The panchromatic image may be reduced in definition, to prevent high frequency signal components interfering with the colour signal carriers, by forming the intervening portions 9b of element 9 as plural, narrow oblique cylindrical elements which diffuse the image, Fig. 11 (not shown). Reference is made to detail modifications involving relay lenses, fibre optics and dichroic reflective filters. A second embodiment of the invention, Figs. 12-18 (not shown), utilizes a colour filter composed of alternate red and blue strips. With this arrangement a single colour carrier signal is produced which is modulated alternately with the red and blue information. Accurate demodulation necessitates the provision of a reference signal. For this purpose a light source is provided in association with the colour filter. The lens elements 9a form images of the source and set up a repeating light pattern which give rise to a distinguishable signal component in the signal output from the pick-up tube. The component is separated and used to furnish a reference signal of the same frequency as the colour carrier. In one arrangement, Fig. 19 (not shown), the light source is a point source, in another arrangement a line source is used. In the detailed arrangement described with reference to Figs. 12-18 (not shown), the source comprises a planar electroluminescent element located in the image light path in front of the optical filter and constructed so as to produce a light distribution varying in the line scan direction (i.e. transverse the axes of the lens elements of element 9) according to the sum of two sine waves of different frequency. The light pattern which results on the pick-up tube gives rise to two signal components which are separated out from the complex video signal and then combined to control the production of the difference signal. Reference is made to detail modifications involving a filter involving red, green and blue elements, and the use of relay lenses and fibre optics. A diaphragm for use with the invention, Fig. 21 (not shown) comprises one or two opaque plates which move transverse the optical path in the region of the colour filter.