GB1189202A - Colour Detection using a Chromic Absorption Filter - Google Patents

Abstract

1,189,202. Colour television. BELL & HOWELL CO. 28 April, 1967, No. 19785/67. Heading H4F. [Also in Division G2] Light from an object is passed along two different paths, in one of which is disposed a colour filter, in the other no filter, or a neutral filter, the two images being formed in black and white. By comparing the optical densities of corresponding parts of the two images, the original colouring of the object may be reconstructed. Fig. 1 shows light from an object 10 passing through a lens system 11 to a beamsplitter 12. Part of the light then passes along path 14, through a neutral filter 16 having an optical density of 0À5 to all visible wavelengths, to be recorded as a black and white image on film 18. The other part of the light passes along path 20 through a variable density filter 21 to be recorded as a black and white image on film 24. If filter 21 is most transmissive to blue, and least to red, then a blue portion of object 10 will show up as denser on film 24 than on film 18. A red portion will show up as less dense, and a green portion as about the same. The films 18 and 24 may be replaced by black and white television cameras 42 and 44, Fig. 3. The signals from the two cameras are fed to a comparer 34, the difference between them developing a chromatic electrical signal which, together with a light intensity signal from the first camera, is fed to a television colour circuit which presents a colour picture of the original object on a colour television tube 38.