Adding Gradations to a Configuration
Gradations are curves that can be applied to the individual data channels after color conversion. The procedure is similar to that for controlling the curves when imaging printing plates. Tone value corrections can be applied to both CMYK channels and to spot color channels with the help of gradations.
To apply gradation curves to otherwise print ready data with ZePrA, create corresponding configurations using the Auto Setup Wizard. The document color space will not be changed.
It is best to apply pure gradation corrections to print ready PDF/X 1a files that are comprised of only CMYK and possibly spot colors. For more detailed information Special Settings/Create Gradations and Automatic Setup Wizard – Apply gradation curves only.
Via the Configurations option on the Navigation Panel, access the Define Configuration window and the Gradations tab. Not only can gradation adjustments be applied in the form of predefined gradation curves, but also gradation adjustments can be imported from an external file and automatically applied to process and spot colors. This is also possible without any prior color management on process and/or spot colors. When updating the curves in this external file, the gradation curves are automatically adopted in the ZePrA configuration and applied to the printing data being processed. This enables short term adjustments of the pronging data without having to change the CTP curves in the RIP. With ZePrA, automatic color and printing control is possible not only for standard printing processes but also for digital printing machines. The gradation curves can be applied to both CMYK and the spot color changes of the file to be converted.
Use the checkboxes to specify whether the gradations are applied only to Images or also to Vector Graphics. The basic colors Cyan, Magenta, Yellow, Black, as well as the entry All Spot Colors appear as fixed values at the top of the list and cannot be deleted or renamed. With the All Spot Colors entry, many spot colors can be adjusted in the document quickly. When activating All Spot Colors and assigning a gradation, all DeviceN spot colors will be adjusted using the same gradation curve. Further entries for adjusting the gradation of spot colors can be in the bottom of the window by creating a new spot color via New, enabling the checkbox and entering the Channel Name and selecting the required gradation curve.
Importing CTP Compensation Curves
Utilizing ZePrA to automate a workflow using external gradation files and import existing CTP compensation curves or correction gradations into ZePrA, a separate tool will be necessary that calculate the respective correction curves based on measurements on printed sheets and saves them into the following form as text or XML files:
GRAY CMYK_C CMYK_M CMYK_Y CMYK_K
0.00 0.00 0.00 0.00 0.00
1.00 0.69 0.58 0.53 0.65
3.00 2.02 1.76 1.62 1.92
5.00 3.23 2.60 2.38 3.28
10.00 6.95 5.92 5.52 7.41
15.00 10.80 9.64 9.02 11.93
20.00 15.10 13.29 12.43 16.68
25.00 19.53 17.19 16.06 21.52
30.00 24.07 21.88 20.37 26.37
35.00 29.08 26.91 24.94 31.26
40.00 34.12 31.50 28.69 36.24
45.00 39.33 36.43 32.94 41.68
50.00 43.80 41.84 37.96 46.59
55.00 49.20 47.98 43.81 51.42
60.00 55.37 54.01 50.29 57.48
65.00 61.91 60.59 57.36 63.44
70.00 68.46 66.28 63.78 69.11
75.00 74.90 72.54 70.73 74.58
80.00 79.24 78.89 77.66 79.52
85.00 85.08 83.09 82.28 84.93
90.00 89.42 87.13 86.64 89.33
95.00 93.74 92.60 92.40 94.02
97.00 95.66 95.25 95.13 96.03
99.00 98.18 98.01 97.98 98.31
100.00 100.00 100.00 100.00 100.00
In this example, Gray stands for the input values in percent (0-100%) and CMYK_C stands for the output values of the Cyan channel in percent (0- 100%). The example shows a step wedge with 25 gradations of the process colors in CMYK. The number of levels is arbitrary and depends on the measuring wedge.
Note: The curves created using ZePrA or curves duplicated from imported text files are stored as one-channel ICC DeviceLink profiles in the profiles folder of the operating system. The drop down menu shows not only the curves supplied with ZePrA for tone value corrections from -20% to +20%, but all Gray-to-Gray DeviceLink profiles contained in the profiles folder of the operating system. Please note that only the curves created in ZePrA can be edited in ZePrA. Imported text files are stored internally and temporarily, but not as DeviceLink profiles. A separate license is necessary in order to be able to use the Gradation functions. Read-only gradation curves can be duplicated in curve management and these duplicates can be edited.
Automatic Gradation Correction of an Existing Configuration
To furnish existing configurations with the required gradation adjustments using an external file and automate the workflow, follow the listed instructions:
- Open the Apply Gradations tab in the Define Configurations window
- Click the Import button
- Select the external file with the required gradation adjustments
In some situations, the format will need to be changed in the Import dialog from configuration file (*.ccf) to text file (*.txt) to be able to import the gradation file. ZePrA assigns the gradation curves found in the file automatically to the right process colors. If spot color curves are also stored in the external gradation file, ZePrA creates the corresponding spot color channel names in the configuration and assigns the appropriate curve to each color.The curve loaded for the selected channel is displayed in a small overview chart.
The configuration is now linked with the external gradation file. If the file is updated because of new measurements on the printed sheet and needs to be overwritten with new gradation curves, ZePrA recognizes the changes and automatically adopts the updated curves.
Gradation curves that originated from loaded text files can be deleted using the Create Gradations dialog. When deleting gradations that are still being used in Configurations, a warning will appear. If this warning is ignored, the gradations in the respective configuration will be deleted and replaced with a linear gradation. Ultimately, when deleting one curve not only the single curve but all curves linked with the file will be deleted.
Applying Gradation Curves to Spot Color Channels
To be able to apply gradation curves to spot color channels, select New and enter the exact name of the spot color. The name of the spot color channel must match the name used for the spot color in the file.
Example: If the spot color names in the file have different naming conventions, work with wildcard characters when entering the channel name e.g, to process a spot color Pantone 123c or Pantone 123 CVC with the same curve, use the (?) wildcard to replace exactly one number/letter combination behind the wildcard or use the (*) wildcard to replace all combinations. Calling a spot color Pantone 123* in ZePrA will allow the set curve to be applied to spot colors in the document that are called Pantone 123C or Pantone 123 CVC.
ZePrA differentiates between upper and lower case. A spot color created in the documents in all upper case will still be adjusted using the set gradation curve even if it was lower case in ZePrA.
In the Gradations tab, choose from three options to perform a gradation correction for spot colors:
- Import existing CTP compensation curves or curves created for gradation correction (read more about this in the chapter Special Settings/Create Gradation Curves). Gradation corrections from an external file may contain more than 16 spot colors and a corresponding number of curves. The XML file format is supported.
Note: If changes are made to the gradation corrections in the external file, ZePrA incorporates them “on-the-fly”. As of now, currently added spot colors with gradation curves are not automatically added in ZePrA. To do this, the file needs to be re-imported.
- Select the Cyan, Magenta, Yellow or Black gradation under the Gradation option. Gradation corrections for spot colors are performed with the same dot gains as the color channels Cyan, Magenta, Yellow or Black during conversion from document color space to target color space.
Note: If spot colors are to be preserved and printed as additional channels, then the dot gain must also be balanced out for the spot colors for color conversion from, for example, coated to uncoated paper. If no dot gain measurements are available spot colors, many users use the Black channel as an approximation of the dot gain curve for the spot color.
- Standard curves are available with an average tvi value increase of -20% to +20% in 5% increments and all Gray ICC DeviceLinks present. The Gray-to-Gray DeviceLinks permit accurate mapping of a tone value correction curve.
Note: To apply the set spot colors and gradation corrections of one configuration to a different configuration, use the Export button to export all channel names and settings of a configuration. The Import button can be used to adopt an exported setting in a different configuration. Identical channel names are overwritten when importing.