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Abstract

In color printing, it is customary to analyze the color content of an original using red, blue and green filters and to make color-component printers for the complementary colors, i.e. cyan, magenta, and yellow, with or without a black printer. The present invention concerns the preparation of a special color printer for a printing ink the color of which is not complementary to one of the said filters, for example a brown separation. According to the invention, sets of values (Ybr, Mbr, Cbr) defining the characteristic elements of curves for yellow, magenta and cyan, which curves together correspond to a range of values for the required color separation, are stored. For each picture element, a combination of color-component values for yellow, magenta and cyan (Y, M, C), are derived and are compared with different sets of values (Ybr, Mbr, Cbr) derived from the stored curve elements, each set corresponding to a different value of the required special-color separation (Br). A value is selected for the desired special-color separation for which each of the stored values of the related set (Ybr, Mbr, Cbr) is not greater than the corresponding value (Y, M, C) derived from the picture element of the original. When, in addition to the color-component signals derived for a picture element of the original, a black signal is also derived, the stored curve-representing values for the special-color separation may include values defining a curve for black.

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First Claim