Patent GB-1197481-A (GB)
Title: Colour Video Signal Generating System
IPC: H04N9/077
Filed: 1967-07-18
Abstract: 1,197,481. Colour television cameras. NIPPON COLUMBIA CO. Ltd. 18 July, 1967 [19 July, 1966 (4)1, No. 33029/67. Heading H4F. A colour video signal generating system for producing a plurality of continuous primary colour video signals comprises a single one-gun camera tube 2, Fig. 1, and an optical filter 4 disposed in the optical path of the camera tube, the filter having strip elements 4W, 4R and 4B as shown in Fig. 2, which pass all colours from an object, interrupt or pass light of one colour from the object, and interrupt or pass light of another different colour from the object respectively. In the embodiments described in detail strip elements 4R and 4B interrupt red and blue light respectively. The video signal E C  from camera 2 (vidicon or image orthicon) is amplified 5 and fed to integrating circuits 8W, 8R and 8G via gate circuits 7W, 7R and 7B, and simultaneously to an index signal generating circuit 9 e.g. discriminator means, which produces a pulse P Q , Fig. 3 (not shown), at the termination of each interval Tw of the video signal corresponding to strip elements 4W (the video signal for interval T w  exceeds the video signals during the intervals TR and TB corresponding to strip elements 4R and 4B), the pulses P O  being applied to a gate signal generating circuit 10 which produces gates signals for gates 7W, 7R and 7B occurring respectively during the intervals TW, TR and TB. The integrated signals, which comprise continuous video signals, are passed to a matrix 11 which derives the three primary colour signals. The strip elements may have equal or different widths and are either arranged perpendicular to or at an oblique angle to the electron beam scanning direction. Gate circuit 7W of Fig. 1 may be omitted, Fig. 4 (not shown), so that circuit 8W integrates the components of all the intervals. In a second embodiment, Fig. 5A, which is similar to Fig. 1, the colour signals obtained at output terminals 11R and 11B are supplied to gates 12R and 12B controlled by the gate signals from circuit 10 to derive colour signals ER<SP>111</SP> in intervals T w  and T B  and colour signals EB<SP>111</SP> in intervals T w  and T R  which are fed to a subtractor 13 with colour signal Ec. A video signal Egh is obtained which represents a green component and is free from limitation upon band width. Signal Egh is supplied to mixer circuits 15R, 15G and 15B through a high pass filter 14 simultaneously with the signals at terminals 11R, 11G and 11B to derive signals Ep<SP>11</SP>, E G <SP>11</SP> and E B <SP>11</SP> each containing a higher frequency component i.e. a green component, which improves the resolution. Gate circuit 7W may be omitted Fig. 5B (not shown). In a further embodiment Fig. 7A (not shown), the elements succeeding filter 14 in Fig. 5A are omitted, so that the video signal Egh from subtractor 13 (contains its lower frequency component since it does not pass through filter 14) is obtained at an output terminal as a green video signal, and the other two colour video signals comprise signals E R <SP>1</SP> and E B <SP>1</SP>. The higher frequency component of the green signal may be substituted for the higher frequency component of the luminance signal. Gate circuit 7W may be omitted, Fig. 7B (not shown). By optically limiting the maximum frequency of the signals related to the red and blue light below the optical filter pitch frequency f o , e.g. to f/O 2 , moire fringes are avoided. This may be effected (1) by arranging for objective lens 3a, Fig. 1, to have a decreased resolution for red and blue coloured lights with respect to the green light, or (2) by utilizing a dichroic mirror to separate the green light from the red and blue light and inserting a lenticular lens or roughened glass plate in the red and blue light path, Fig. 8 (not shown), or (3) a filter may be disposed in the light path having a different refractive index (multilayer interference) regions scattered therein for the red and blue coloured lights e.g. the filter may comprise a glass plate having two sets of dot-like multilayer filter elements having different refractive indices (which may be equal) for red and blue lights from that of the glass plate Figs. 9A and 9B (not shown). The optical filter 4, Fig. 2, may include black strip filter elements from which pulses PO are derived, alternatively a light of a particular colour may be reflected by means of a translucent mirror on to the optical filter 4 so that pulses PO may be positively obtained even if the luminosity of the object is low Fig. 10 (not shown). Further to assure that pulses PO may be positively produced the transmittivities of elements 4W of filter 4 for red, green and blue light are arranged to be higher than for elements 4R and 4B, so that the amplitude of the video signal is greater during intervals TW than during the other intervals even for monochromatic light. A filter having elements 4R and 4B which pass respectively red and blue light only may be utilized in the systems described with respect to Figs. 1-4. In a further embodiment Fig. 11 (not shown), the image of the object is projected on to a monochrome photographic film via optical filter 4, and the developed film is optically picked up by means of a one-gun video camera tube or by means of a flying-spot scanning tube and an associated photo-electric device.