Patent GB-672492-A (GB)
Title: Negative-positive colour photography involving colour connection
IPC: G03C7/18
Filed: 1950-06-27
Abstract: 672,492. Colour photography involving colour correction. KODAK, Ltd. June 27, 1950 [June 28, 1949], No. 15988/50. Class 98 (ii). A first photographic material comprising three selectively sensitized silver halide emulsions is exposed to a coloured object and processed to produce three subtractively coloured dye images, one or two of such dye images being negative images and the remaining two or one being positive images; and a second photographic material comprising three further selectively sensitized silver halide emulsions is exposed to light passing through all the images of the first material and processed to produce three subtractively coloured dye images, of which those corresponding to the negative image or images of the first material are negative thereto and therefore positive to the coloured object and those corresponding to the positive image or images of the first material are positive thereto and therefore positive to the coloured object. As shown, light from an object having black, blue, green, red and white portions affects the several layers of a film comprising a cellulose ester support 10, a red-sensitive silver halide emulsion layer 11 free of coupler compound, a green-sensitive silver halide emulsion layer 12 containing a magenta coupler and a bluesensitive silver halide emulsion layer 13 containing a yellow coupler (which may overlie a yellow filter layer) in the places of the arrowheads. The film is colour developed, to produce a silver negative image in area 14 of layer 11, silver and magenta dye images in areas 15 of layer 12, and silver and yellow dye images in areas 16 of layer 13, as shown in the second stage of the drawings. Development of all exposed silver halide is completed by a. black- and-white developer, the film is washed, exposed with red light through the support, colour developed in a colour developer containing cyan colour former, fixed in acid hypo, washed'and bleached as in alkaline ferricyanide, fixed and washed, to produce a cyan dye positive image in area 17 of layer 11, as shown in the third stage of the drawings. The result is printed with white light on to a material similar to that of stage 1, but which may, if desired, have an opaque support, whereby the cyan positive image 17 and the overlying magenta image 15 act, mutually, as filter masks for each other to compensate for unwanted green and red absorptions of the cyan and magenta dyes respectively. The printed material is colour developed with the result of the fourth stage of the drawings-a support 20 having red-sensitive layer 21 containing a silver negative image 24, green-sensitive layer 22 containing magenta dye and silver positive images 25, and bluesensitive layer 23 containing yellow dye and silver positive images 26. Layer 21 is then exposed with red light, developed in cyan colour forming developer as was layer 11 of the second stage, and after bleaching and fixing the film appears as shown in the last stage of the drawings with cyan 27, magenta 25 and yellow 26 images corresponding to the original object. By a corresponding procedure any one or two positive colour images with two or one negative images may be produced in the first material, to result in three subtractively coloured images in the second material. Natural or false colour procedure may be used. The method may be applied to single layer elements of the mixed grain type. Couplers in the emulsions are not essential since multilayer materials may be colour developed by methods of controlled diffusion of the processing solutions. The method of the invention as applied to colour correction of dye images produced by bleaching out uniformly dyed emulsion layers in the regions of silver images is described. Specifications 475,784, 475,786, 477,524, 541,589 and 546,704 are referred to.