Method for controlling the application of ink in a printing press and computer program product for implementing the method

1. A method for controlling an application of ink in a printing press, the method comprising the following steps:

predefining at least one setpoint color value in a device-independent color space;

activating an ink metering element in the printing press with an ink application value to produce, on a printing material, an ink layer thickness associated with the setpoint color value;

determining at least one actual color value of the ink layer thickness produced on the printing material in the device-independent color space;

carrying out an activation with a changed ink application value as a function of a deviation of the actual color value from the setpoint color value, to produce an ink layer thickness differing from the ink layer thickness produced;

determining the changed ink application value by calculating a necessary ink layer thickness change as a function of changes in the color values in the device-independent color space in the event of a change in the ink layer thickness at a point of the actual color value, the changes in the color values in the device-independent color space in the event of a change in the ink layer thickness being partial derivatives of the color values in the device-independent color space with respect to the ink layer thickness; and

calculating the ink layer thickness change dF in accordance with a formula:

dF =(Δ S i *ΔLab I i )/|Δ S|^ 2,

where ΔS=(∂L/∂S, ∂a/∂S, ∂b/∂S, ∂I/∂S) at a point LabI actual ,

ΔLabI=LabI actual −LabI setpoint ,

i counts off vector components, and

summation is carried out over i=1, 2, 3 and 4.

2. The method according to claim 1 , wherein the device-independent color space is the LabI color space.

3. The method according to claim 1 , which further comprises determining the partial derivatives numerically from an assignment of device-dependent tonal values to a device-dependent color space.

4. The method according to claim 1 , which further comprises representing an assignment of the color values in the device-independent color space to the changes in the color values in the event of a change in the ink layer thickness as linking an assignment of the color values in the device-independent color space to tonal values in a device-dependent color space with an assignment of the tonal values in the device-dependent color space to the changes in the color values in the event of a change in the ink layer thickness.

5. The method according to claim 1 , which further comprises carrying out the production of the ink layer thickness on the printing material in an offset printing process.

6. The method according to claim 1 , which further comprises carrying out the method for a plurality of colors in a multicolor print.

7. The method according to claim 1 , which further comprises carrying out the method in a plurality of physical zones each being associated with a respective ink metering element.

8. The method according to claim 1 , which further comprises calculating a plurality of ink layer thickness changes at a plurality of positions on the printing material and determining a mean value thereof used to determine the changed ink application value.

9. The method according to claim 1 , which further comprises:

following a change in the ink application value, for the activation of the ink metering element, determining at least one actual color value of the ink layer thickness produced on the printing material by the ink metering element activated with the changed ink application value in the device-independent color space; and

carrying out changes in the ink application value for the activation of the ink metering element until the deviation of the actual color value from the setpoint color value lies within a specific tolerance.

10. A computer program product to be loaded directly into an internal memory of a digital computer and/or stored on a computer-suitable medium, the computer program product comprising software code sections for implementing all of the steps of the method according to claim 1 when the product runs on the computer.