ZePrA’s Spot Color Iteration
Spot Color Iteration is a process that involves printing of the spot colors converted from ZePrA on the printer to be used for the print job, followed by measuring test charts and optimizing the color differences (expressed in deltaE2000) until the measured deltaE values are within the desired tolerances. Printing the test chart and applying the Iterate Spot Colors feature once only already results in an improved spot color rendering which is usually close to the optimum of this printer.
Why can spot color iteration be required?
First of all, be assured that ZePrA already calculates the best possible spot color conversion based on the target profile set under Configuration/Target Color Space. However, printers, inks and papers drift over time so that there are always some deviations from the state the printer was profiled. During spot color iteration we measure how converted spot colors are actually printed in the current state, and subsequently optimize the deltaE2000 values. The iteration report shows which colors are improved and where restrictions based on the color gamut or the spot color Calculation Method occur so they can’t be optimized further or if additional iteration steps are recommendable.
Open the Iterate Spot Colors dialog right from the Spot Colors tab of the Configuration you would like to optimize or the Tools menu and follow the steps from top to bottom. A Spot Color module license is required to use the tool.
Step 1: First, select the Configuration you would like to use for printing. The option Convert Spot Colors must be enabled in this configuration.
Notes: The best approach for the iteration of spot colors is to set the Calculation Method to Precise Match or Visual Match in the appropriate Configuration.
The setting Use the least Amount of Channels may be insufficient for iterating spot colors. Importantly, spot color iteration will not work when the spot color conversion is set to Convert using Alternate Color Space from PDF.
Step 2: Select the source of the spot colors you would like to optimize. You can either choose a PDF or an image file with spot colors or a complete spot color library. In the following example we will use a PDF file with spot colors as source file.
Step 3: A test chart file will be created from either a PDF or Image File or a spot color Library. If you select a PDF file and click on the Save button, ZePrA will extract all spot colors (full tones) used in the file and convert them using the selected configuration. In this step select an Instrument Setting for your measuring instrument. In the Save dialog, choose either a PDF or TIFF file type to create a test chart which contains the spot colors as a strip optimized for your measuring instrument. In addition, the associated reference file for measuring will be created. The newly created test chart needs to be printed on the printer to be used for the print job.
Note: The test chart contains the converted spot colors as given in the Configuration using the conversion settings and Calculation Method defined in the tab Spot Colors.
Step 4: Print the test chart on your printer. Do not apply any color management when printing the test chart.
Step 5: Subsequently, measure the printed test chart using ColorAnt/Measure Tool or an appropriate software. The required reference file which is needed for measuring the spot colors will be shown in step 3. Click on Measure to open the Measure Tool in ColorAnt. The reference file will be selected automatically so that you can use the tool right away for measurements with your instrument. For information on how to use the Measure Tool in combination with your instrument follow the instruction given in the online help. Alternatively you may use the provided reference file for measurements with other tools.
Step 6: This step is optional but highly recommended. If you click on Save Report a Spot Color Iteration Report will be generated. The report provides you with information about the achieved and measured deltaE values.
The last column of the report – Status – provides status information such as improvements, recommendations about further processing or warnings. If the deltaE00 value is already very low (lower than 1) further optimization is not needed and the color is marked green. Colors that are marked yellow are higher than 1 but below 2 dE00 and colors marked orange are higher than 2 dE00. For colors that have been improved by an iteration the improved value is shown in brackets expressed as deltaE behind the status. If a spot color is out of gamut or optimization is not possible due to restraints from the selected configuration those colors are marked accordingly. A Legend below the table of the report explains the different statuses. If a color is marked as Optimizable, the value in brackets behind the status indicates the maximum improvement to be expected.
Step 7: When clicking the Apply button the optimized spot colors (based on the measurement data) will be calculated and applied in the Configuration. Only tick the checkbox Iterate all Spot Colors if you would like to iterate all spot colors. We recommend to deactivate the checkbox in order to include only those spot colors in the iteration which can actually be improved. Consequently, if the checkbox is disabled, spot colors which are already marked as Good in the report will not be optimized further.
A feedback message informs the user when a spot color iteration has been applied successfully.
You will find the optimized device values (Output values) in the table of the tab Spot Colors under Configuration. They will be marked as Iterated in the column Information of the table.
Expert tips: It is a good idea to Export the optimized spot color table of the tab Spot Colors. This will give you the chance to revert to these values in case you do some further iterations or change some values manually. Another tip in case you would like to revert to the original values without iteration is to use the Reset button in the Spot Color Iteration dialog. This deletes the iterated colors from the table.
If you would like to evaluate the improvements in terms of deltaE2000 after Step 7 you need to print the optimized spot colors once more. To do so click on the Save button in Step 3 of the Iterate Spot Colors dialog to create a new test chart file with the optimized device values and a new reference file. Make sure to use the second testchart file when printing and measuring rather than the first one! After measuring and saving a new Report you can assess the improved deltaE00 values. You can continue to iterate by simply clicking the Apply button in Step 7. Or, in case the deltaEs are fine and further iteration is not recommended, simply close the dialog without applying the new measurements.
If the selected source file does contain spot colors which have not been considered in the selected configuration, an error message will appear as the test chart cannot be created. For that reason we recommend to convert the source file containing the spot colors integrating the wanted configuration prior to the iteration, or to verify them using the Spot Color Report in order to ensure correct settings in the configuration.
If you would like to optimize the creation of the test chart for you measuring device (for Step 3 of the iteration) you can create your own settings using the tool Export Chart in ColorAnt. The newly created settings are available in the drop-down menu Instrument Setting after the dialog Spot Color Iteration has been closed and reopened.
The measurement data that has been transmitted from Measure Tool to ZePrA in Step 5 is saved for later use in the shared folder for all users under ColorLogic/SpotColorMeasurements (Windows: C:\Users\Public\Documents\ColorLogic\SpotColorMeasurements. Mac: \Users\Shared\ColorLogic\SpotColorMeasurements).