Method of color correct manufacturing decorative panels

1. A method of manufacturing decorative panels comprising:

inkjet printing, by an inkjet printing system, an oligochromatic pattern on a substrate to form a decorative layer;

impregnating, by a resin impregnator, the decorative layer with a thermosetting resin;

heat pressing, by a heating press, the impregnated decorative layer together with a core layer to form a decorative panel; and

identifying, by a color control unit, a color acceptance of the decorative panel after forming the decorative layer and before impregnating the decorative layer, wherein said identifying comprises:

determining a first color value at a coordinate of the oligochromatic pattern;

color measuring a second color value by using a color measuring device on a position of the decorative layer, wherein the position corresponds to said coordinate and the color measuring device is connected to said color control unit;

converting with a color conversion model the second color value to a third color value, wherein the color conversion model is pre-determined after forming the decorative layer and before forming the decorative panel;

comparing the first color value and the third color value to determine the color acceptance of the decorative panel by calculating a color difference of said first color value and said third color value and checking if said color difference is within a desired color difference range.

2. The method of claim 1 , wherein the method further comprises:

determining a dominant color value of the oligochromatic pattern before inkjet printing, wherein the first color value is said determined dominant color value.

3. The method of claim 2 , wherein determining a dominant color value comprises:

determining an image-gamut in an N-dimensional device independent color system of the oligochromatic pattern;

thinning the image-gamut to a skeleton in said N-dimensional device independent color system;

selecting a point on said skeleton as the dominant color value, wherein the point is substantially an inflection point, a cross point, or an end point.

4. The method of claim 2 , wherein determining a dominant color value comprises:

determining an image-gamut in an N-dimensional device independent color system of the oligochromatic pattern;

clustering color values in the image-gamut into K clusters by K-means clustering;

selecting a cluster of said K clusters; and

selecting a point of the cluster as the dominant color value, wherein the point is substantially a centroid of the cluster or a point in the cluster with one or more of the substantially highest chroma and the substantially lowest luminance.

5. The method of claim 1 , wherein the method further comprises:

determining the first color value of the oligochromatic pattern before inkjet printing by:

determining an image-gamut in a N-dimensional device independent color system of said oligochromatic pattern, wherein N>1 and said image-gamut comprises color values of said oligochromatic pattern; and

determining a skeleton of said image-gamut, wherein the skeleton comprises a plurality of points, wherein the plurality of points are determined by:

selecting a luminance-range for color values in said N-dimensional device independent color system;

determining a sub-image-gamut of said image-gamut, wherein said sub-image-gamut corresponds to said luminance-range and comprises color values which have a luminance in said corresponding luminance range; and

determining a color value in said sub-image-gamut as a point of said skeleton, wherein the first color value is a color value in said sub-image-gamut with a minimum color difference between said selected color value and said skeleton smaller than 3 ΔE CIELAB,94 .

6. The method of claim 5 , wherein said color value in said sub-image-gamut is a balance point of the sub-image-gamut, wherein said balance point is a point that fulfills a predetermined condition based on the collection of N-dimensional points of said sub-image-gamut.

7. The method of claim 6 , wherein the balance point is substantially a centroid of the sub-image-gamut.

8. The method of claim 6 , wherein the selected color value is one or more of an end point, an inflection point, and a cross point of said skeleton.

9. The method of claim 1 , wherein the second color value is measured by a spectrophotometer, a line camera system, or a spectral linescan camera system.

10. The method of claim 9 , wherein said inkjet printing system comprises an info generator and the method comprises generating the identified color acceptance for viewing by an operator of the inkjet printing system.

11. The method of claim 9 , further comprising marking the substrate when the color acceptance is out the desired range for the color acceptance.

12. The method of claim 9 , wherein the inkjet printing system comprises:

a set of printheads for printing the oligochromatic pattern with a set of color channels; and

a control system; and

the method further comprises one or more of:

adapting a minimum luminance jettable by said set of printheads according the desired range for the color acceptance; and

adapting one or more of brightness and luminance of a color channel of said set of color channels according to the desired range for the color acceptance.

13. The method of claim 9 , wherein the substrate has a porosity according to Gurley's method (DIN 53120) of between 8 and 25 seconds.

14. The method of claim 13 , wherein the substrate has a paper weight between 50 and 170 g/m 2 .

15. The method of claim 14 , wherein the substrate is a paper substrate having on one or more ink-receiving layers.