GB437888A - Improvements in printing or reproducing colour photographs - Google Patents

Abstract

437,888. Colour photography. HARRISON, G. B., and THREADGOLD, S. D., 23, Roden Street, Ilford, Essex. May, 2, 1934, No. 13311. [Class 98 (ii)] Relates to printing by contact from a multicolour-screen master photograph made on regular-pattern screen material onto multicolour-screen copy material of any pattern, using a printing light comprising a number of light sources of different colours corresponding to the screen colours, each colour having the same spectral range as, or a narrower range than, the corresponding screen colour, and consists in choosing the effective dimensions of the source of each colour in a plane parallel to the screen, and the distance of the source from the master screen, so that, having regard to the usual slight separation of the master and copy screens, the light from that source which is passed by a master screen element of the same colour spreads over an area of the copy screen substantially equal to the area of a group of colour elements forming a master screen pattern unit. The light source of each colour may consist of a single source or of several sources of that colour ; and the complete source may consist of a source of white light, or a source of light as described in Specification 417,860, with a diffusing screen or equivalent lens system, between which and the master and copy is placed a mask carrying colour filters spaced apart over its surface. If two filters of different colour overlap, a single filter transmitting both colours may be employed at the overlap. A mask for use when the master screen is of the kind described in Specification 322,432, [Class 98 (ii)], comprising red lines 1, Fig. 2, separated by alternating blue and green rectangles 2, 3, comprises an opaque sheet 8, Fig. 3, having apertures fitted with red, green, and blue filters 9, 10, 11 respectively, the filters being arranged so that the red spread the light transversely to the direction of the master screen red lines, and the blue and green spread the light both parallel and transversely to the master screen lines. Fig. 4 shows the manner in which the red sources, when placed at a predetermined distance from the master screen 12, cause light passing through a red element 14 of the master screen to spread on the copy screen 13. The filters for different colours may be of different size according to the size of the elements on the master screen ; and other slight variations may be made for the purpose of colour correction or for compensating for irregularities in the master screen element. A modified form of mask is described in the provisional specification comprising three red filters arranged in line transversely to the screen lines, three green filters arranged in line parallel to the screen lines, and a single central blue filter. Specification 374,891 also is referred to.