Patent GB-747611-A (GB)
Title: Improvements in or relating to a colour separation system, particularly with reference to colour television systems
IPC: H04N9/16
Filed: 1952-11-20
Abstract: 747,611. Cathode-ray tubes. LA VIA, J. Nov. 20, 1952, No. 29366/52. Class 39 (1). [Also in Group XL (b)] A colour filter system, preferably for colour television transmitters or receivers, comprises an ionic crystal target scanned by an electron beam which is cyclically interrupted successively at a plurality of different constant frequencies each much greater than the scanning frequency, each interruption frequency being representative of the occlusion band of the crystal for filtration of a desired primary colour, i.e. the colour transmitted depends on the interruption frequency. Alternatively for monochrome systems the beam is interrupted at a single fixed frequency. In a transmitter, Fig. 2, the screen is composite and comprises halide layers 22, 30, transparent metal layers 21, 23, 31 and glass support S. Ribbon beam from gun 24 extending the full width of the screen is swept vertically upwards over halide layer 22 and is interrupted by a constant frequency applied to control electrode 27. This frequency is such that each elemental area receives a plurality of bunches of electrons during each scan which set up distinctive interference phenomena in the halide layer and consequently only one component of light, e.g. red, can pass, i.e. the halide layer acts as a red filter. Halide layer 30 is stated to be photoconductive so that it takes up a representation of the red partial image and on scanning by a second beam from gun 32 video signals are generated across output resistor 37. This procedure is repeated for the blue and green components by altering the interruption frequency applied to control electrode 27. The beam from gun 32 scans two interlaced fields for each complete scan of the beam from gun 24. Suitable potential differences are maintained between the metal layers 21, 23, 31. In another transmitting arrangement, Fig. 1 (not shown), a single halide layer backed by a transparent metal layer and exposed to the light image is scanned by an electron beam interrupted successively at three frequencies corresponding to the desired colour components, the frequency being changed for each successive elemental area, i.e: a dot sequential system. Line sequential systems, a given line being scanned three times successively before the next alternate line is scanned, or field or frame sequential systems, may be used. In dot sequential systems the beam may trace out a large number of small triangles. In a colour receiver, Fig. 5, the beam scanning a potassium halide target 43 is modulated with video colour signals and interrupted successively at the frequencies corresponding to the desired colours, and a beam of light from source 40 is projected through the halide 43 on to a viewing screen 50. The halide has transparent anode layer 44. A switch S enables change over to monochrome operation by maintaining the interruption frequency constant, at the red, blue or green level. In another form, Fig. 6 (not shown), the light source 40 is replaced by a fluorescent layer on the halide surface, the layer emitting white light when scanned by the beam which also penetrates to the halide. In another colour receiver, Fig. 7, the device has two guns 63, 64, a monochrome image being formed by scanning halide layer 74 and an interrupted ribbon beam sweeping upwards over halide layer 75 to convert it into a colour filter for each of the three colours successively. A beam of light 60 is projected through the halide layers to form a projected image on screen 84. The beam from gun 63 scans two interlaced fields for a single scan of the beam from gun 64.