Patent ID: 8708439

Claim:
A method of operating a printing press, comprising the steps of: transferring ink from an inlet point to a printing substrate via at least one ink supply system; measuring actual optical values (I) of light by at least one optical measuring device, said actual optical values (I) being intensity values of light in a selected wavelength range and the light having undergone an interaction with at least parts of a print image; measuring and/or estimating a mass of the ink contained in said at least one ink supply system by using an ink mass determination device; feeding the values from the optical measuring device and from the ink mass determination device to a control and evaluation device; determining an optical deviation (ΔK) that is a deviation of the actual optical values (I) from optical reference values (S), which are also available as light intensity values (L) of selected wavelength ranges, by said control and evaluation device; and determining on a basis of the optical deviation and the values from the ink mass determination device, an amount of corrective ink having a determined composition that is to be fed to the printing press in order to approximate the actual optical values (I) to the optical reference values (S) by said control and computing device, with different printing jobs being performed sequentially with said printing press, and an equal optical reference value (S) with regard to at least one colour underlying at least two of said different printing jobs for at least one colour, with measured values and/or ink formulas of a former of said at least two different printing jobs being taken into account for supplying of the ink mixture for a later one of the at least two printing jobs, with one of said measured values being the deviation (ΔK), which results from the former of the at least two different printing jobs, when the printing substrate was printed with an ink mixture, which was used to attain the optical reference value (S), and with composition and/or formulas of the ink mixtures, which led to the deviations (ΔK, ΔK 1 , ΔK 2 ) of said optical measured values (I) from the optical reference values (S), being taken into account.