Creating Color Definitions

Requires an additional license.

In GMG OpenColor, Separation Rules are used to define color separations for a fixed ink setup / ECG. The rules are basically a lookup table of input colors (spot colors) from the document and define how the input colors should be separated into the output inks of the separation target color space as defined in the project.

You can use the color definitions for multiple purposes:

  • For manual separations in any third-party application: Simply manually transfer percentage values from the Separation Rules to your image editor. You do not need to waste time playing around with different output ink configurations and percentage values anymore, but you can see right away the color definition that will provide the best match and the expected delta E.
  • For automatic or semi-automatic separations in the third party application PACKZ: PACKZ uses the Separation Rules as default settings for separations. You will still be able to finetune the separation in PACKZ, but the Separation Rules allow you to use consistent color definitions and to save time as you can reuse existing definitions.
  • For automatic separations in GMG ColorServer.
  • For statistical purposes, for example, to check the color match and look for out-of-gamut colors: You can export the color definition table and import it into a spread-sheet editor.

This video shows how you can define your spot colors in GMG OpenColor using Separation Rules. See how easily you can control the used color separations and other options. It also shows how you can apply the defined separations to your printing PDF, using GMG ColorServer, GMG ColorPlugin, or Hybrid PACKZ.

How does it work?

Per default, GMG OpenColor uses a best match algorithm for creating a color definition, that means, the application calculates the color definition with the lowest possible delta E (compared with the target values of the input colors). However, you can customize the separation rules to your needs, for example, you can remove inks with a very low percentage or limit the total number of inks used, or manually edit the percentage values.

Separation Rules dialog box.

The matrix shows the following values:

  Description
1 Input color (as it appears in the document you want to separate)
2 Output inks in percent (how the input color will be separated)
3 Target Mode (from the input project, see Correcting the Target Color and the Tone Value Curve) Use Absolute if the printed spot color should match the swatch book as closely as possible. Absolute is the best option for most applications.
4 Target Lab values (from the input project, how the input color would ideally be printed)
5 Current Lab values (actual printed color)
6 Delta E values (difference between the target color and the actual printed color)
7 Status of the color definition. When manually editing output inks, you will need to recalculate the color definition.
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Color variant: You can add new color variants by clicking the Add Ink Variant button on the right side. In the example screenshot, a variant for PANTONE 228 C, which uses Violet and Yellow instead of CMK, has been created.

To remove an output ink from the separation, click the icon next to the percentage value in the list until the cross icon appears. The ink will not be used.

To enable the output ink again, click the icon until the gearwheel icon appears.

To enter a fixed percentage value for an output ink, click the icon until the edit icon appears. Enter a custom percentage value. This value will be used for the separation of the solid color.
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You can click the Calculate button to start the calculation of new or edited color definitions (that are in status Pending Calculation). Colors in status Ready will not be recalculated.

You can change the calculation settings above the list, for example, the Max Number of Output Inks before starting a new calculation (see "Calculation settings"). These settings are applied only when a new calculation is started. Colors in status Ready will not be changed.

If you want to recalculate the entire color list, for example, because you changed a calculation option such as the number of output inks, you can reset the list by clicking the Reset Calculation button. Custom values will be preserved.

In the Separation Rules window, you will be notified if the separation rules are not synchronized with the input project, i.e. if input colors have been changed without recalculating the color list. The message Show Changes and the number of different input colors will be displayed (see "Changing colors").

You can click the Save data and jump to input project button to navigate directly to the input project to change the input colors.

You can export a Separation Rule as a .txt file to analyze it in a spreadsheet application such as Microsoft Excel, e.g. to detect "out of gamut" colors. You can export it as a db3 spot color database for use in GMG ColorServer.

You can click the Generate ColorBook button to create a ColorBook PDF and then print it directly on your press (see "Show the Full Potential of Your Press").
10 Ink priorities: The preference to use an output ink over the other is indicated by the order of sequence from left to right. You can change the ink priority by drag-and-drop. In the example screenshot, the CMYK inks have a higher priority than the additional inks. Of course, GMG OpenColor still prefers an ink with a lower priority if a better match with the target values can be found.

When saving Separation Rules, make sure that all color definitions are in status Ready. Otherwise, you will not be able to select or use the Separation Rules in PACKZ.

  1. In a Project, click Separation on the main panel.
  2. Click Separation Rule on the Tools & Actions panel.
    The Select Project dialog box lists all projects that are available as input color spaces. You can define only one Separation Rule per input and output project combination. Therefore, projects that are already used in a Separation Rule for the currently active project will not be shown in this list. (To edit an existing Separation Rule, click the Edit button on the right side.)
  3. Select the input color space.
    The shown Separation Rules matrix defines the relationship between the input inks on the left and the output inks on the right.
  4. Start the calculation.
    GMG OpenColor will calculate best match values for each input/output combination, i. e. find the best match with the target value as defined in the characterization of the input color space. This means, the input inks will be reproduced as good as technically possible in the target printing process.

You can define the Total Area Coverage and the overprint behavior under Screening and Usage in the Ink Settings dialog box in the project.

Existing separation rules will not be updated when the Total Area Coverage or overprint behavior in the Ink Settings are changed. There will be no information on inconsistencies. You will need to update separation rules manually by clicking the Reset Calculation button in the Edit Separation Rules dialog box.

See also:

Available options Description
First Printing Dot Affects the Separation Rules calculation. Output channel values below this percentage value will be set to 0%. Helps to avoid Min Dot problems in flexo printing.
Last Printing Dot Affects the Separation Rules calculation. Output channel values above this percentage value will be set to 100%.
Output Inks (Max) Defines the maximum number (between 1 and 4) of output inks that will be used in the separation of the input color. The priority of the output inks is defined by the order of sequence from left to right and can be changed by the user. For example, if you have 5 output inks available in the separation Target Color Space, you can enter the number "3" to use only 3 inks per input color. Limiting the number of output inks can be a requirement for special packaging applications. It also can enhance the stability of the printing process and save money, because less inks are used. On the other hand, this means a compromise on matching the input color as defined by the designer. GMG OpenColor shows you the expected deviation in delta E and helps you to make the best decision for your specific project.
Controlled Ink Reduction

Under Controlled Ink Reduction, you can basically choose between low delta E and reduced number of output inks.

If No Reduction is selected, the number of output inks will be limited only by Output Inks (Max). GMG OpenColor will use a best match algorithm for calculating the solids, that means, the application calculates the color definition with the lowest possible delta E (compared with the target values of the input colors). For the tints, the same output colors will be used as for its parent solid, even if this is not the best match.

With the following options, you can reduce the number of output inks. This will generally result in a higher delta E.

Use the option Generate Preferably CMYK to separate colors into CMYK if the color deviation is not bigger than the set tolerance. Only if the deviation is bigger than the entered delta E, GMG OpenColor will use all available output inks. Generate Preferably CMYK saves costs, but decreases color accuracy.

Generate Preferably CMYK supersedes the ink priority. If this option is selected, CMYK will be used preferably even if, for example, Blue has the highest priority. However, if the priority is set to KCMY, K will have the highest priority.

If you selected Custom Reduction, GMG OpenColor will check for each color, whether it is possible to reduce the number of output inks without exceeding the set delta E tolerance.

Example: If Custom Reduction is selected and the tolerance is set to 1.00, GMG OpenColor will check whether the number of inks can be reduced to one. If the predicted color difference is below 1 delta E, only one output ink will be used. If this is not the case, GMG OpenColor checks next whether the number of inks can be reduced to two. If the predicted color difference is below 1 delta E, only two output inks will be used. And so on.
Icon Output Ink Usage Description
Automatic (best match) GMG OpenColor will calculate the percentage value of this ink to achieve a best match with the target color.
Disabled This output ink will not be used for the separation of the input color.
Fixed custom value The custom percentage value will be used for the separation of the solid input color. You can use this feature to fix or manually change the current percentage value. When recalculating the color definition, fixed values will not be changed. (Of course the color definition needs to be adapted when a tint of the input color is going to be separated.)
Icon Action Description
Show tints Shows the tints of the color.
Add ink alternative Adds a new variant (with alternative output ink values) of the color.

You might want to do the following after the color definitions have been initially calculated:

  1. Change the scope of available spot colors in the spot color library (on characterization level), i.e. add a new spot color, delete a spot color, activate and deactivate a spot color.
  2. Apply Color Corrections to spot colors (on characterization or project level).
  3. Edit the Inks list in the input project.
  4. Change the ink set (output inks) your press is using in the output project.

All colors affected by those changes need to be recalculated. In case (a), i.e. editing the spot colors in a spot color library, GMG OpenColor will automatically update all depending separation rules (see "Automatic update of Separation Rules"). In all other cases, you will need to open all separation rules using this spot color library as input color space and manually start the update (see "Manually updating Separation Rules").

When a spot color has been added to, deleted from, activated or deactivated within a spot color library, GMG OpenColor will automatically update all depending Separation Rules.

GMG OpenColor will notify you with the option to Update if the spot color library is used in at least one set of Separation Rules.

After you clicked Update, GMG OpenColor will automatically recalculate all depending Separation Rules.

After you clicked the Cancel button, you will not be able to trigger the automatic update anymore. You will need to open all separation rules using this spot color library as input color space and manually start the update (see "Manually updating Separation Rules").

Waiting and ongoing recalculations are listed in the Tasks dialog box. The affected sets of Separation Rules will be locked for editing until the update will have been finished. GMG ColorServer will automatically synchronize all depending spot color libraries (in case the automatic synchronization has been activated in GMG ColorServer) after the update will have been finished.

You can manually update the Separation Rules list by opening it from the output project.

In the Separation Rules window, you will be notified if the separation rules are not synchronized with the input project, i.e. if input colors have been changed without recalculating the color list. The message Show Changes and the number of different input colors will be displayed.

You can click the eye button to show only the differences between the current list and the input project.

In the differences view, you can you can click the Sync with input project button to update the entire color list. You can also pick a specific color and update only this color.

Input colors that are not available anymore, because they have been removed or deactivated in the project used as input color space will be removed from the Separation Rule list. New input colors will be added to the list. Changes to the target Lab values coming from changes applied to the Media or as a result of Color Corrections on the Project level will be applied. Your target values will be up-to-date and in line with the target values of the proof profile created from this project.

You can also click the Save data and jump to input project button (2) to navigate directly to the input project, to change the input colors there.

All custom values will be kept when a recalculation takes place.

See also: