Patent GB-726881-A (GB)
Title: Improvements in method of projecting television images in color
IPC: H04N9/31
Filed: 1953-09-14
Abstract: 726,881. Television; light valves. CHROMATIC TELEVISION LABORATORIES, Inc. Sept. 14, 1953 [Sept. 17, 1952], No. 25356/53. Class 40 (3). In a colour television receiver projection system employing a light valve of the type in which light from a local source is modulated by the deformations produced in a deformable medium when scanned by a modulated electron beam(s) a repeating sequence of colour filter strips is positioned in the incident light beam and a plurality of cylindrical lenses is positioned in the path of the scanning electron beam(s) and serves to direct the beam(s) on to areas of the medium corresponding to selected colour filter strips. In the embodiment shown in Fig. 1, the light valve comprises a slowly rotating shallow pool of oil 21, the scanned area of which is included in the optical path between a local light source 11 and a projection viewing screen 27 the path further including plane mirrors 12, 26 and Schlieren optical devices 13, 14 and 24, 25. The lower wall 16 of the oil container 20 which is provided with a repeating series of colour filter strips 17, 18, 19 extending throughout the scanned area and located above the oil surface and extending parallel to the colour filter strips there is positioned a grid assembly comprising a plurality of wires 22 between which and the transparent conductive lower wall a potential difference is maintained so that the wires form a plurality of electrons " cylindrical " lenses. In the embodiment of Fig. 1, the wires 22 are all maintained at the same potential and the three electron guns 23, each of which is assigned to a different component colour, are aligned such that the deformations produced by the scanning beams, which scan the oil surface in lines parallel to or perpendicular to the filter strips, occur in sections of the oil surface in optical relationship with the filter strips of corresponding colour. In this manner a colour image is produced on the projection screen 27. Fig. 5 shows part of the arrangement employed in an alternative embodiment which employs a single electron gun to which the received signals are supplied. In this arrangement the grid wires 22 are connected in two groups, as shown, between which a switching potential in synchronism with the received signals is applied to deflect the scanning beam on to an area of the oil surface above a colour filter strip appropriate to the instantaneous colour modulation of the scanning beam. In this case the filter strips are in the repeating order R.G.B.G. (or similar order) instead of the repeating order R.G.B. as in the embodiment of Fig. 1. Instead of employing refraction of light passing through the oil layer the oil layer light reflected from the oil surface may be used to produce the image. Rotation of the container 20 (which, together with the electron gun(s) is enclosed in an evacuated chamber) serves to cool the oil surface and a " doctor " blade is employed to smooth the surface to prevent persistence of deformation by charges accumulated thereon. The arrangement may be employed in colour television systems of any type, e.g. simultaneous, sequential (frame, line or dot) and the scanning beams may be either amplitude or velocity modulated.