METHOD FOR AUTOMATED GENERATION OF REFERENCE COLOR VALUES FOR COLOR CONTROL

Abstract

A method for the automated generation of reference color values for color control purposes in a printing machine by using a computer includes, within a process of setting up the printing machine for a print job, initially carrying out printing operations and using a spectrophotometer to determine coloration values for every process color used in the print job. For every process color that is used in the print job, the computer automatically selects that coloration value of a process color that has the smallest deviation from a color set point that has been established at the beginning of the job and saves this coloration value as a new reference value for this process color.

Claims

1. A method for the automated generation of reference color values for color control in a printing machine by using a computer, the method comprising the following steps: within a process of setting up the printing machine for a print job, initially carrying out printing operations and using a spectrophotometer to determine coloration values for every process color used in the print job; using the computer to automatically select a coloration value of a process color having a smallest deviation from a color set point having been established at a beginning of the print job for every process color being used; and using the computer to save the coloration value as a new reference value for the process color.

2. The method according to claim 1, which further comprises in addition to the coloration values, using the spectrometer or a densitometer or a combination measuring head including a spectrometer and a densitometer to determine color density values of the process colors being used.

3. The method according to claim 2, which further comprises saving the selected reference color values as CIE Lab values of respective process colors being used, and additionally saving CIE Lab values of the printing substrate as well as color density values for respective process colors being used as a color set.

4. The method according to claim 1, wherein the printing machine is a sheet-fed lithographic offset printing press.

5. The method according to claim 2, which further comprises using the spectrometer to determine the coloration and color density values for every process color in every ink zone and subsequently using the computer to select an ink zone having measured values with a smallest deviation from the color set point having been set at a beginning of the print job for the process color.

6. The method according to claim 5, which further comprises: using the computer to display to an operator on a display device all ink zones with the corresponding reference color value and the corresponding color density value for all process colors being used; optically marking the selected ink zones; and using an input device to provide the operator with an option of at least one of manually selecting a different ink zone for all process colors being used or manually modifying the reference color value and the color density value established for the selected ink zone.

7. The method according to claim 6, which further comprises: displaying, in addition to the ink zones, job data for a current print job including at least one of a customer's name, a job number, a paper type being used and a paper class; and saving the generated color sets with the determined reference color value and the color density value under the customer's name or job number locally on the computer or in a database.

8. The method according to claim 2, which further comprises in a first step, using the computer to download standard reference color values for the process colors being used from a color set saved in a database and using the computer to generate the new reference color values and color density values based thereon.

9. The method according to claim 2, which further comprises, for every process color used in the print job, using the same spectrometer, densitometer, or combination measuring head of the same color system for the coloration and color density values determined for the generation of the reference values and at the same time in the printing process as the established color values during the actual color control process for processing the print job.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0038] FIG. 1 is a diagrammatic plan view of a GUI (Graphical User Interface) overview of generated reference color values;

[0039] FIG. 2 is a block diagram of a printing machine system in which the method of the invention is used; and

[0040] FIG. 3 is a schematic flow chart of the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0041] Referring now in detail to the figures of the drawings, in which identical reference symbols identify identical elements, and first, particularly, to FIG. 2 thereof, it is seen that the method of the invention in its preferred embodiment is used in a printing machine system 2 which is shown in a block diagram. The system includes a printing machine 3 that is to be calibrated for a pending print job. The printing machine 3 is monitored by a control unit 4 that has access to a database 5 in which color sets 6 of the inks that have been used so far are saved.

[0042] In order for the desired set-up time optimization to become effective, the printing machine 3 needs to be set up in an optimum way and the target colorations adapted to the ink/paper combination that will be used absolutely need to be available in the color measuring system as reference values 6 in the form of spectrums, CIEL*a*b values 16, and densities 18. In practice, it is precisely these data which are missing because an operator 1 may need many training sessions to make correct inputs and may find inputting the data too complex, difficult to understand, and not transparent. As a result, attaining the desired coloration result 15 on the printed sheet still takes too much time and creates too much waste.

[0043] Thus, it is strongly recommended that the operator 1 be given a chance to save optimum colorations that have been attained before in such a way as to make them readily and easily retrievable in an uncomplicated way not only for this job but for all further print jobs that have an identical coloration target. The method of the invention provides a way to do this. A diagrammatic flow chart of the method of the invention is shown in FIG. 3.

[0044] In a first step, the operator 1 will always need a standard reference color value as a starting point for printing. The reference color value may be taken from a spot color archive or from a so-called standard color set 17. Up to this point, the method corresponds to the prior art. In accordance with the prior art, once the desired reference coloration has been attained, the operator 1 would manually check whether or not the attained reference coloration 16, 18 matches the desired result 15. If this is not the case, the operator would continue to make manual changes until the print result looks good or matches a pre-defined sample. In general, this is done by modifying the target values in the color settings of the printing machine 3.

[0045] FIG. 1 illustrates a preferred embodiment in the form of a graphical user interface 14 of the control unit 4 for carrying out the method of the invention.

[0046] In this case, the process is different. Once the printing operation has started, reference color values 16 for all ink zones are measured by using a spectrophotometer. The reference color values 16 are then displayed to the operator 1 in the graphical user interface 14 on a display of the control unit of the printing machine 3. In the preferred embodiment shown in FIG. 1, these are the process colors orange 8, black 9, cyan 10, magenta 11, and yellow 12. The coloration overview is always geared to the target coloration 15 and indicates when the latter is attained. The control unit 4 then automatically selects a value 7 of the ink zone that is closest to the target coloration 15, simultaneously marking the selected values 7 in the graphical user interface. In the preferred embodiment shown in FIG. 1, this is illustrated for the reference color values 7. Additionally, however, the process is carried out in a similar way for the measured color density values 18.

[0047] Once the selected reference color values and reference density values have been displayed to the operator 1, the latter may make manual changes 19′. This may be desirable, for instance, if no measured reference color value of a specific ink zone 16 comes close to the target coloration 15. In this case, the operator 1 needs to make manual changes. The measured reference color values 16 for the process color orange 8 are an example of this because all of the measured reference color values 16 for all ink zones greatly deviate from the color set points 15. If the operator 1 pushes the “modify” button 13, he or she may either click on the reference color value 16 of a different ink zone in the overview or he or she may input values 16 manually. If the density values 18 are changed, the reference color values 16 need to change in a corresponding way and vice versa. The operator may likewise change the names. Then the color set 19′ is saved and is then available for all measuring systems. The selected reference color values 7 are then saved as a color set 6 in a modified version 19′ or in a non-modified version 19, respectively. Then they are used for the print job and are additionally saved in the database 5 for a future use of the same process color.

[0048] For this purpose, the button “save target values” 13 is to be provided directly on the user interface 14 for all measuring systems.

[0049] In addition, the customer's name and paper being used are automatically extracted from the job data and added to an overview. In this way, the color set 6 is unequivocally retrievable in the database 5 and associated with the customer. If a different paper than the one that has been saved is used at a later point, the operator 1 will know immediately that he or she may have to create a new color set 6.

[0050] If no customer name and/or paper type was given or is available, the job number and paper class are indicated. The font type or color is changed in order to highlight information.

[0051] In addition to its simplicity, a great advantage of this method is that at the instant of the measurement, the process color is in precisely the same state in which all future measurements and control operations of the regular color control system will be carried out. This is not the case in the prior art where process colors are remeasured at a later point and have already diffused into the paper or dried oxidatively.

[0052] The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: [0053] 1 operator [0054] 2 printing machine system [0055] 3 printing machine [0056] 4 control unit [0057] 5 database [0058] 6 color set saved in a database including reference color values and reference density values [0059] 7 selected reference color value [0060] 8 used process color “orange” [0061] 9 used process color “black” [0062] 10 used process color “cyan” [0063] 11 used process color “magenta” [0064] 12 used process color “yellow” [0065] 13 button for saving the selected reference color values [0066] 14 graphical user interface [0067] 15 color set point [0068] 16 measured reference color value [0069] 17 standard color set [0070] 18 measured color density value [0071] 19 color set including selected reference color values and reference density values [0072] 19 color set including manually modified reference color values and reference density values