Patent GB-568196-A (GB)
Title: Improvements in subtractive colour photography
IPC: G03C7/18
Filed: 1943-07-29
Abstract: 568, 196. Colour photography. KODAK, Ltd., (Eastman Kodak Co., Evans, R. M., and Hanson, W. T.). July 29, 1943, No. 12313. Drawings to Specification. [Class 98 (ii)] A colour-correcting mask in registry with a subtractive multi-coloured photographic transparency which is being copied comprises a record of selected light passed through the transparency, processed to a dyed relief image of complementary character (i.e. a negative if the transparency is a positive, and vice versa), and of lower absorption gamma. The mask may be adhesively secured to the transparency, or the sensitive material in which it is to be produced may be so secured and may remain attached until the copy has been printed from the combined mask and transparency ; the mask may be made by passing through the transparency red light, or light wholly transmitted by the yellow image but absorbed by the magenta and cyan images in the relative proportions in which blue light is absorbed by them, e.g. as described in Specification 551,614, or white light to yield a mask containing a record of all the colours of the original as described in Specification 512,608 ; it may be dyed grey (e.g. with Comacid Black), or with one or more dyes (e.g. Orange II, Alizarin Astrol, Anthraquinone Blue-green) yielding a coloured or grey image ; the grey or coloured image may be retouched generally or locally to add, remove, or substitute grey or colour ; and may be coloured in accordance with the principles set forth in Specifications 553,196, 553,229 and 553,230. The copy may be printed on multilayer colour-sensitive material and processed by colour development. In an example, an unhardened red-sensitive silver halide emulsion layer containing gelatin or other colloid, and carried by a support as of cellulose ester, is exposed to red light through a subtractive multicolour transparency produced, e.g. as described in Specification 507,841, the layer is processed in known manner to a negative colloid relief image which is thereafter dyed and, if desired, retouched as set out above, it is then applied in registry to the transparency, and a colour print is made from the combination. The red-sensitive layer may be temporarily dyed with a cyan dye, removable in the processing baths, in order to depress the gamma of the relief image. The procedure may be modified by transferring into adhesive contact with the transparency a light-sensitive layer on a water-impermeable support, as from a stripping film of the kind described in Specification 555,383, so that the said support lies between the light-sensitive layer and the transparency in order to prevent degradation of the colours of the transparency during the processing of the mask in the light-sensitive layer, which remains on the transparency during all the operations of producing the mask therein, and printing a copy from the combination. The invention simplifies colour correction with a, separate mask in that, if comparison of the copy with the original transparency indicates unsatisfactory correction, the dye may be removed from the relief and this may be dyed afresh ; in the case of colour correction with an adherent mask, removal of the dye from the relief permits the same comparison to be made, since it will not be hindered by the presence of the uncoloured relief, whereafter the relief may be re-dyed in the same or a different way.