| 摘要 |
In colour printing, it is customary to analyse the colour content of an original using red, blue and green filters and to make colour-component printers for the complementary colours, i.e. cyan, magenta, and yellow, with or without a black printer. The present invention concerns the preparation of a special colour printer for a printing ink the colour 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 colour separation, are stored. For each picture element, a combination of colour-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-colour separation (Br). A value is selected for the desired special-colour 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 colour-component signals derived for a picture element of the original, a black signal is also derived, the stored curve-representing values for the special-colour separation may include values defining a curve for black. |
