Patent GB-788127-A (GB)
Title: Photographic elements and processes of photography
IPC: G03C7/18
Filed: 1955-10-25
Abstract: 788,127. Colour photography. DU PONT DE NEMOURS & CO., E. I. Oct. 25, 1955 [Nov. 12, 1954], No. 30554/55. Drawings to Specification. Class 98(2) A dye mask image is formed in a colour photographic film comprising at least one silver halide emulsion layer which is lightresponsive primarily to one of the regions blue, green or red of the spectrum and containing a non-diffusing colour former capable on colour development of forming a subtractive dye having essentially one of the complementary colours, but which has an unwanted absorption in some other part of the spectrum, and at least one auxiliary slow speed silver halide emulsion layer responsive primarily to radiation above 700 mÁ and containing a non- diffusing colour former capable on colour development of yielding a dye having an absorption in said region of unwanted absorption of the first dye, by exposing the film to radiation above 700 mÁ during colour development. Examples are given of correcting for the unwanted blue absorption of a magenta image formed in a single blue- or green-sensitive layer by using an adjacent low speed infra-red emulsion (such as a Lipmann emulsion), containing a yellow colour former and exposing the film from either side to infrared radiation during colour development to form a mask in the low speed layer. Similarly the unwanted blue and green absorption of the cyan dye in a redsensitive layer is corrected by forming a mask in an adjacent infra-red layer containing a yellow (arid optionally also a magenta) colour former. The film may be the usual multilayer one and may be developed to a negative or even to a positive if it is to be used in some further copying process. Thus it may comprise a base coated with green, red and blue sensitive layers or red, green and blue sensitive layers in that order, with a yellow filter layer under the top blue sensitive layer. Many examples are given of the latter arrangement with different colour formers in the various layers. Thus the layers may contain cyan, yellow and magenta colour formers respectively (in the red, green and blue sensitive layers) and the unwanted blue absorption of the magenta dye may be corrected by a yellow mask formed in an infra-red emulsion either above or below the top emulsion or beneath the yellow filter layer. An orange dye mask (which may be obtained from a mixture of yellow and magenta colour formers) may be formed adjacent the bottom cyan image to correct for the unwanted blue and green absorptions of the cyan dye and also to correct the magenta dye. The latter may be further corrected by a yellow mask as described above. A film containing magenta, yellow and cyan images respectively may be similarly corrected with yellow and/or orange masks. Alternatively the colour formers may be in the order cyan, magenta and yellow (in top blue sensitive layer), and an orange dye mask formed in an infrared sensitive layer between the magenta and cyan dye images may correct for both the latter dye images, or the unwanted blue absorption of both magenta and cyan images may be corrected by a yellow mask adjacent the magenta image layer, and the unwanted green absorption of the cyan image by a magenta dye mask adjacent the cyan image layer. In further examples, the colour formers are in the order magenta, cyan and yellow respectively and an orange mask is formed between the cyan and magenta layers or a yellow mask adjacent the magenta layer and an orange (which may be yellow or magenta), or magenta mask adjacent the cyan layer. In all cases the masks are formed by exposure through either or both sides to infra-red radiation during colour development. Specifications 535,341, 627,125, 627,353, 635,294, 640,122, 646,348, 647,638, 662,793, 663,190, 705,950, 720,284, 739,851 and U.S.A. Specifications 2,179,244 and 2,272,191 are referred to.