Method for dynamic printing process calibration

Abstract

A method for the dynamic printing process calibration of a printing press includes determining a calibration dataset for the colored halftones of the process colors, determining a calibration dataset for the gray halftones of the process colors, determining a weighting factor for the two calibration datasets as a function of the original print and calculating a combined calibration dataset from the two determined calibration datasets, with reference to the weighting factor. The calculated combined calibration dataset is applied to the calibration of the printing process of a printing press.

Claims

1. A method for a dynamic printing process calibration of a printing press, the method comprising the following steps: determining a calibration dataset for colored halftones of process colors; determining a calibration dataset for gray halftones of the process colors; determining a weighting factor for the two calibration datasets as a function of an original print; calculating a combined calibration dataset from the two determined calibration datasets, with reference to the weighting factor; and applying the calculated combined calibration dataset to the calibration of the printing process of a printing press.

2. The method according to claim 1, which further comprises carrying out the determination of the calibration dataset for the colored halftones of the process colors by measuring and evaluating at least one control element having colored halftones and adapting the halftones of the process colors while incorporating measured results and a set of characterization data describing the printing process.

3. The method according to claim 1, which further comprises carrying out the determination of the calibration dataset for the gray halftones of the process colors by measuring and evaluating at least one gray value control element and adapting the gray values of the process colors while incorporating measured results and a set of characterization data describing the printing process.

4. The method according to claim 1, which further comprises determining the weighting factor by using an automatic analysis of image content of the original print.

5. The method according to claim 1, which further comprises defining the weighting factor manually by a user.

6. The method according to claim 1, wherein the weighting factor includes different values with a continuous transition for different halftone areas, depending on an image content of the original print.

7. The method according to claim 1, which further comprises: creating a third calibration dataset from multidimensional transformation tables, in addition to the calibration datasets for the colored and gray halftones of the process colors; including a weighting factor from the third calibration dataset; and calculating a combined calibration dataset from all three present calibration datasets.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a flow diagram showing the basic sequence of the method according to the invention;

(2) FIG. 2 is a flow diagram showing the sequence of adapting the colored tonal value gain;

(3) FIG. 3 is a flow diagram showing the sequence of adapting the gray value reproduction;

(4) FIG. 4 is a diagram showing an example of a calibration dataset with a distribution of 0% colored tonal value gain to 100% gray value reproduction;

(5) FIG. 5 is a diagram showing an example of a calibration dataset with a distribution of 50% colored tonal value gain to 50% gray value reproduction; and

(6) FIG. 6 is a diagram showing an example of a calibration dataset with a distribution of 100% colored tonal value gain to 0% gray value reproduction.

DETAILED DESCRIPTION OF THE INVENTION

(7) Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a preferred embodiment variant of the method according to the invention. The preferred embodiment variant primarily includes a combination of two methods for adapting a colored tonal value gain and a gray reproduction. Both methods are carried out in a first step. They are illustrated in simplified form in FIGS. 2 and 3.

(8) The adaptation of the tonal value gain and of the gray reproduction is carried out through 1-dimensional correction files in a raster image processor (RIP) during an exposure of printing plates. The correction files are generated by specialized programs which include both measured values of targets 8 and 9 and target values of the adaptation as input values. Preferred target values in the preferred embodiment are characterization data 2, which describes the printing process to be calibrated. Preferred measured values 8 and 9 are values from measured print control elements 1 and 3. In the method for adapting the colored tonal value gain, these are step wedges of the process colors. One example is the print control element for the colored halftones ECITVI10 1. In the method for adapting the gray reproduction, these are in turn specific gray control elements, such as the print control element P2P25 3. The calibration files are determined from the measured values and target values in accordance with both methods D.sub.tvi 4 and D.sub.gray 5 by using the common methods.

(9) Two datasets 3 and 4 are thus present, from which a combined total calibration dataset D.sub.tot 7 is calculated, with the aid of a weighting factor f 6.

(10) The weighting factor 6 is chosen as a function of the original to be printed, that is of the subject. If the subject is gray-toned, as is frequently the case in technical areas, a small value of f is chosen. If the subject is colored and has few to no gray tones, as is the case in landscape recording or portraits, a high value of f is chosen. The calculation of the weighting factor 6 can be made manually by the user or in the context of an automatic analysis of the original. In this case, the original print, which is in any case normally present in digital form, is analyzed by a program on a computer with respect to the distribution between colored and gray halftones. The weighting factor 6 is then determined by the program depending on the distribution. Manual re-correction of the automatically determined weighting factor 6 is also possible.

(11) A factor of f=1.0 results in a pure colored tonal value gain adaptation, a factor f=0.0 in turn results in a pure gray reproduction adaptation, and a value between 1 and 0 results in a combined adaptation with different emphases.

(12) The weighting factor 6 can be carried out as a function of halftone range in a further embodiment variant, which means that for different halftone ranges, different values with a continuous transition are provided. This makes sense, for example, if gray tones are present in the light area and more chromatic colors are present in the medium and darker lightness range.

(13) Once the weighting factor 6 has been determined, a common dataset is calculated from the two individual calibration datasets D.sub.tvi 4 and D.sub.gray 5. This is done in accordance with the following formulae:
C.sub.new[n]=f*C.sub.tvi[n]+(1f)* C.sub.gray[n];
M.sub.new[n]=f * M.sub.tvi[n]+(1f)* M.sub.gray[n];
Ynew[n]=f*Y.sub.tvi[n]+(1f)* Y.sub.gray[n];
K.sub.new[n]=f* K.sub.tvi[n]+(1f)* K.sub.graY[n].

(14) Each dataset then includes the respective N correction values of the process colors CMYK. The combined correction values are the weighted mean of the individual correction values.

(15) FIGS. 4, 5 and 6 show exemplary calibration datasets 10, 11 and 12. The measured value datasets 9 and 10 are produced in this case from a P2P25 Target 3, which contains both the needed information for the colored tonal value gain calibration and the gray balance calibration. The reference printing condition is a characterization dataset 2 for an offset printing process. In this case, FIG. 4 shows the calibration data and curves 10 by way of example for a pure calibration of the gray balance. The weighting factor 6 is thus f=0.0 in this case. In FIG. 5, in turn, mixed calibration data and curves 11 with an equivalent incorporation of the two partial datasets D.sub.tvi 4 and D.sub.gray 5 are shown. In this case, the weighting factor 6 is appropriately f=0.5. FIG. 6, finally, shows the calibration data and curves 12 for a pure calibration of the colored halftones. The weighting factor 6 is f=1.0.

(16) In a last step, the printing process is then calibrated dynamically, i.e. adapted to the requirements arising from the original print, by using the calculated common calibration dataset D.sub.tot 7.