Method of stipulating values for use in the control of a printing machine

A method for stipulating a desired-color locus of a measurement field in a, preferably digital, original image to derive signals to control an ink feed in a printing machine making copies of said image, said method comprising:

• dividing the measurement field into a plurality of area elements;
• calculating, for an area element j of the plurality of area elements, a relative area Aij to be printed by a printing ink i with a known spectral distribution Si where the subscript i represents a specific ink;
• estimating an area-element-color distribution by summing, over all the inks to be used in printing, a product of the relative area Aij and the corresponding spectral distribution of the ink i, and a weight αi which is initially set to 1;
• estimating an actual-color distribution for the measurement field by combining the area-element-color distributions for each of the area-elements in the measurement field;
• estimating an actual-color density distribution from the actual-color distribution;
• estimating an actual-color locus from the actual-color density distribution;
• determining a new value for the weight, αi corresponding to the printing ink i such that the desired-color locus and the actual-color locus are within a stipulated tolerance color offset;
• choosing αi, if more than one choice is possible, so that the sum over index i, corresponding to the printing inks, of (1−αi)2 is a minimum, and at least one αi is not equal to one;
• and
• printing an area equal to (Aij)(αi) with printing ink i.

A method for determining preset values for the manufacture of multi-color printed examples on a printing press, the printing press working by autotype, wherein with a master in at least one image element with given proportions of areas to be printed, the method comprising the steps of:

• coordinating a plurality of individual inks to be used on printing to a spectral reflection desired value and to this at least one spectral desired reflection value on the subsequent print is brought into use in combination with a spectral reflection actual value for the manufacture of positioning commands for an ink feed;
• using a representation of a spectral reflection of multi-color image elements (cx, cy;
• mx, my) as a coefficient containing linear combination from proportions of a surface to be printed as well as a spectra of the individual inks;
• prescribing for each image element (cx, cy;
• mx, my) of the master a desired color position to be achieved in a later print such that for each image element (cx, cy;
• mx, my) determination of a desired ink spectrum or of the desired ink density spectrum takes place using a linear combination representing co-printing of the individual inks corresponding to their proportion of surface to be printed within the image element (cx, cy;
• mx, my) in combination with the spectra or ink density spectra of the individual inks;
• providing the spectra or ink density spectra of the individual inks within the surface to be printed with a scaling factor (xi) in each case within the linear combination corresponding to their proportion of printed surface within the image element (cx, cy;
• mx, my) and determining coefficients of the linear combination by varying scaling factors such that a color position emerging from the spectral reflection values in accordance with this linear combination corresponds to the desired color position;
• and
• using the spectral reflection values corresponding to this color position as reflection desired values in subsequent printing operations.