Patent GB-1179273-A (GB)
Title: Apparatus for Receiving a Multicolour Television Picture.
IPC: H04N9/14
Filed: 1967-02-03
Abstract: 1,179,273. Colour television. AGFA-GEVAERT A.G. 3 Feb., 1967 [4 Feb., 1966], No. 5407/67. Heading H4F. The Specification describes an optical-mechanical colour television reproducer, using one or more lasers as the source of the coloured light beams one at least of the lasers providing at least two of the light beams. In the introductory arrangement of Fig. 1, lasers 1, 2 and 3 produce monochromatic blue, red and green light beams respectively which are controlled in intensity according to respective received video signals by respective means 4, 5 and 6. The controlled beams are combined by means of interference reflection filters 7 and 8 into a combined beam which is incident on the mirrored periphery of a rotating Weiller wheel 9. The Weiller wheel comprises a cylindrical arrangement of N/2 mirrors, where N is the number of   lines in the picture to be scanned, each being at a different angle to the axis of the wheel according to the position in the raster of the line to be scanned thereby, the angles of consecutive mirrors varying progressively from the first to the last mirror and the difference in the angles of said first and last mirrors determining the height of the picture. The wheel rotates twice per frame, a first rotation producing the odd lines of a frame, and the second rotation producing the even or interlacing lines of the frame. To produce the one-line position offset between the odd and even lines, two mirrors 11 and 12 are provided, differently inclined so as to reflect the beam from the wheel 9 into position on screen 16 offset by said one line. Mirror 12 is fixed, and mirror 11 is as shown in Fig. 2 and rotates once per picture frame, such that mirror 12 is uncovered to reflect the odd lines for half a frame, and mirror 11 is then interposed to reflect the even lines for the second half of the frame. To reduce the distance to the screen 16, the picture may be focused on an intermediate screen 14, and then projected by lens 15. For a non-interlaced picture, the number of mirrors on the wheel is N, the wheel rotates once per frame, and mirrors 11 and 12 are dispensed with. In an embodiment according to the invention a single laser producing all three colours may be used, the three colours being separated out by interference reflectors, individually modulated, for example by KDP crystals, and then recombined-see Fig. 3 (not shown). In the arrangement of Fig. 4, the combined beam 27 falls on a first polygon mirror 28, comprising, for a 620-line picture, 62 parallel mirrors, and rotating ten times per frame. The thus produced line scans are reflected by a second polygon mirror 30 having an axis at right angles to that of mirror 28. For a non-interlaced picture, mirror 30 rotates such that one mirror thereof scans the beam from the top of the picture to the bottom during said ten rotations of mirror 28. In the case of an interlaced picture, mirror 30 rotates at twice the previous speed, such that one mirror I, Fig. 5, scans all the odd lines in five rotations of mirror 28, and then mirror II, suitably inclined to mirror I, scans all the even lines in the next five rotations of mirror 28.