GB1228878A - - Google Patents

Abstract

1,228,878. Colour reproduction. DAINIPPON SCREEN MFG. CO. Ltd. 30 April, 1968, No. 20462/68. Heading H4F. In a system for providing colour separation signals for printing masters from a scanned colour original, seven output signals are derived corresponding to three primary colour inks, three secondary colour inks and black ink. The three primary inks may be yellow, magenta, and cyan as is conventional and the three secondary inks may be orange, green and violet. Thus instead of overprinting yellow and magenta to produce orange or orange ink is used. As shown, Fig. 2, the red, green and blue components (R, G, B) of the scanned original are applied to known circuitry 7 to derive corresponding yellow, magenta, cyan and black signals y 1 , m 1 , c 1 and k 1 , the black signal k 1 is subtracted from each of the colour signals y 1 , m 1 , c 1 in computers 12, 13, 14 to produce signals Y 2 , m 2 , c 2 which are connected in pairs to minimum value selection circuits 19, 20, 21 which produce orange, green and violet signals o 2 , g 2 , v 2 so that for example o 2 = minimum of y 2 and m 2 . The resulting seven signals are applied to computer units 27 to 33 which contain variable controls for adding or subtracting small proportions of each of the other signals to each signal to correct the signals according to the actual hue of the ink used in the printing process. The resulting signals y 3 , 0 3 , m 3 , v 3 , c 3 , g 3 and k 3 are then applied to under-colour removal circuitry 3. A variable proportion of the black signal k 3 is subtracted from each of the secondary colour signals 0 3 , v 3 , g 3 to produce output signals 0 4 , v 4 , g 4 . Variable proportions of the black signal k 3 and of those two of the secondary colour signals 0 3 , v 3 , g 3 derived in circuit 1 from a primary colour signal are applied to each circuit 88, 89, 90 which select the maximum value (or alternatively the sum) of the input signals and this value is subtracted from the corresponding primary colour signal to produce outputs y 4 , m 4 , c 4 .