GB857654A - Improvements in or relating to colour reproduction systems - Google Patents

Abstract

857,654. Copying by scanning. CROSFIELD Ltd., J. F. July 17, 1959 [July 18, 1958], No. 23162/58. Class 40(3). Relates to a colour reproduction system utilizing a black printer and employing colour correction and undercolour removal. In such a system, Fig. 1, a colour separation printer image is produced by the direct exposure of a photographic plate 18 to a colour separation transparency 10 which is illuminated by scanning light from a source 6, the light also serving to illuminate further transparencies 10 so as to produce signals in photo-electric cells 12 which are applied via a computer 14 to modulate the intensity of the light source so as to reduce the density of a positive image resulting from the exposure in accordance with desired colour correction and undercolour removal. As illustrated, three transparency positions are provided, the photographic plate always being placed in contact with the centre negative. The left-hand negative serves primarily for colour correction whilst the right-hand negative serves for undercolour removal. Figs. 2, 3 and 4 show how the system is set up to produce respectively magenta, yellow and cyan images from red (R), green (G) and blue (B) colour separation negatives and an undercolour removal negative U (see below). The cyan printer, Fig. 4, does not require large colour correction from one of the other colours and is employed to correct itself by bringing into use a photo-electric cell responsive to light traversing the centre transparency and associated photographic plate. For this purpose the photographic plate is backed by a filter 22 which rejects light of a colour to which the plate is sensitive but passes all other colours. This photo-electric cell may also be used in producing yellow and magenta images. The undercolour removal negative U is produced by direct exposure of a photographic plate to white light transmitted through or reflected from the original or by exposure to a number of colour components of the original, the light source having, if desired, a colour bias. Fig. 5 shows how the system is set up for production of a "black printer" image, the photographic plate being placed in contact with the undercolour removal negative, whilst the red and blue negative are employed to produce signals to reduce the image density in coloured areas. According to an alternative method of working, the red negative is used for undercolour removal during production of the magenta and yellow images by increasing its effect to an extent greater than that required for colour correction. Reference is also made to the use of four transparency positions, two being employed for colour correction instead in one as in Fig. 1. The scanning may be effected by the use of a cathode-ray tube light source, as shown in Fig. 1, or a rotating drum or oscillating table. Specification 857,234 is referred to in connection with a method of correcting the characteristic curve of the photographic plate. Specification 835,111 also is referred to.