Creating Color Definitions
Note: 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 (CMYK only).
- 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.
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:
|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)|
|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.|
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 options above the list, for example, the Max Number of Output Inks before starting a new calculation. (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.
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 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. If you want to update the range of available input colors and the target Lab values, you can click the Sync with input project button (only shown in the differences view). 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. Updating the input colors and the target Lab values also means that the output inks will be reset and need to be recalculated, while keeping all custom values.
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.
|9||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 Magenta ink has a higher priority than the PANTONE 240 C ink. Of course, GMG OpenColor still prefers an ink with a lower priority if a better match with the target values can be found.|
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 Yellow 12 C has been created. The best match color uses Yellow and Magenta output inks. The variant uses Yellow and PANTONE 240 C.
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.
Note: 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.
- In a Project, click Separation on the main panel.
- 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.)
- 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.
- 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.
|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%.|
|Max Number of Output Inks||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.|
|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.)|
|Show tints||Shows the tints of the color.|
|Add ink alternative||Adds a new variant (with alternative output ink values) of the color.|