Patent GB-777969-A (GB)
Title: Transmitting and receiving of coloured images
IPC: H04N11/02
Filed: 1954-10-05
Abstract: 777,969. Colour television. RUDATIS, D. A. Oct. 5, 1954, No. 28637/54. Class 40 (3). Relates to a system of colour reproduction which utilizes in effect a plurality of independent colour processes, each of which alone is capable of providing an approximately complete representation of all colours in an image to be reproduced. Fig. 1 illustrates in a conventional chromaticity diagram the use of three trichromatic processes comprising respectively the primaries 1-4-7, 2-5-8 and 3-6-9. The spectral extensions of the primaries used for analysis are selected conventionally for each process whereby the colour gamuts reproduced are indicated by the triangles bounding each group of primaries. The use of three processes increases the total gamut of reproduced colours so as to approach more closely the locus of spectral colours 10. Furthermore, since any primary colour is a secondary colour in the other two processes, the reproduction of any colour involves a minimum of five of the total of nine primaries. Thus, primary 1, for example, will be reproduced correctly by process 1-4-7 and will also be reproduced in desaturated form as at IA and 1B respectively by pairs of primaries 5, 8 and 3, 6 in processes 2-5-8 and 3-6-9. The resulting composite reproduction is indicated at 1C and corresponds to a slight reduction over correct saturation. The corresponding effect for the other primaries is indicated at 2A, 2B, 2C, 3A ... 9A, 9B, 9C. The system results in a loss of saturation for all colours and thereby prevents the production of dominant colours by those colours which in any one process are normally reproduced at full saturation whilst the others are reproduced with reduced saturation at the points where they enter the colour triangle. The feature whereby a minimum of five primaries out of nine are always active is utilized to reduce the visibility of the structure of the reproduced image by arranging the mosaic of elemental coloured areas in which the image is analysed and reproduced in the manner shown in Fig. 7. Here each area is numbered in correspondence with utilized primary shown in Fig. 1, successive horizontal lines being displaced and the arrangement along any horizontal line being such that each primary colour is interposed between two others which in the chromaticity diagram occupy spectral positions closer to each other than to the interposed primary. By this means, when a colour is reproduced, the inactive colours along a line are always isolated between active colours and the elemental structure of the image is obscured. Fig. 10, for example, shows the result when reproducing primary 2. In an alternative arrangement, Fig. 8 (not shown), the succession of colours is arranged vertically. In a further arrangement for rendering the visibility of the image structure less noticeable, Fig. 18, the elemental areas employed in the reproduction only are each sub-divided into four equal parts. Two of these arranged diagonally opposite to each other are allotted to the primary colour appropriate to the area whilst the other two are allotted to the two primaries spectrally adjacent the appropriate primary. Thus, as shown in Fig. 18, the first area, for example, has two parts allotted to primary 1 and one to each of adjacent primaries 3 and 8. The combination of primaries 3 and 8 produces a colour closely approximating to primary 1 and the combination of 3 and 8 with 1 results mainly in a slight change in saturation. The invention may be applied to any process for reproducing colour pictures, although it is described more particularly as applied to colour television, Fig. 21 (not shown), where corresponding mosaics of colour filters having characteristics as described above are associated with the cathode-ray camera and reproducing tubes. As an alternative to the use of filters, the camera target may be constructed of suitably different photo-sensitive substances and the reproducing tube screen of suitably different phosphors. The circuit features may be conventional and are not described. Reference is made to the use of three separate camera tubes each arranged for analysis according to a different one of the three trichromatic processes.