GB1092882A - Improvements relating to the generation of electrical signals representing colour components of an image - Google Patents

Abstract

1,092,882. Colour television cameras. ELECTRIC & MUSICAL INDUSTRIES Ltd. May 19, 1964 [May 16, 1963], No. 20563/64. Heading H4F. [Also in Division G2] Image light is focused on the target 3, Fig. 1, of a pick-up tube 2 by a lens 4 and is divided into its component colours by means of two filter gratings 1 which are spaced from each other and are located in the path of the convergent light from the exit pupil of lens to the target in a position so that they are not in focus on the target surface. The Specification discusses the relationships between the grating constants and their spacings from the target which are necessary to produce desired colour shadow patterns whereby the colour components may be distinguished. A first arrangement, Fig. 4, is concerned with the generation of simultaneous colour signals and uses gratings as shown at 9 and 10 with strips disposed at right-angles to the line scanning direction and formed in a repeating sequence of white (W), yellow (Y), cyan (C) and green (G). The gratings allow green light to pass without modification but impose line structures on the red and blue light with the blue pattern period half that of the red. As a consequence, during scanning, green appears as a conventional video signal whilst red and blue appear simultaneously as carrier signals with frequencies in the ratio 1 : 2: Fig. 5 (not shown) illustrates a modification in which the second grating 12 is formed with only white (W) and green or black strips. A second arrangement, Fig. 6, uses gratings as shown at 13 and 14 (the unreferenced shaded strips being black) and produces a shadow pattern giving a light distribution along a scanning line as shown at (c) whereby dot sequential signals are produced. A third arrangement, Fig. 7, is employed for the generation of line-sequential colour signals and utilizes horizontal strip gratings as shown at (a). The green strips are uninterrupted, but the red and blue strips are interrupted by black section as shown shaded. The number of black sections in the blue strips is twice that in the red strips. The vertical light distribution is as shown at (b), the intensity peaks corresponding to scanning line spacing. Red, green and blue signals thus appear in sequence at line rate, the red and blue signals being carrier signals which are distingushed in frequency. This third arrangement may be utilized in the apparatus described in Specification 1,092,881 where the line-sequential signals are subsequently converted to simultaneous signals. The gratings may be in the form of lenticulations which have a focusing effect.