Iterate

Improve DeviceLink profiles

Iterate

Overview

An existing DeviceLink profile can be optimized based on measured color values by using a test chart of your choice (can be created with ColorAnt/Custom Chart). The test chart needs to be converted from source to target profile using the original DeviceLink profile and printed on the target printer. The measured color values of the printed test chart are then used to improve the conversion in order to achieve lower color differences and a more accurate reproduction of the source color space. Based on the measured values, it is automatically determined whether the target values are reached (which are determined by the source and target profiles) and a correction is made for deviations. Iteration is therefore particularly useful in proofing situations with absolute or relative colorimetric rendering intents. Perceptive rendering intents can also be used as a special feature of DeviceLink iteration in CoPrA. The iteration calculates a new DeviceLink profile based on the original DeviceLink profile and the measured values. The new profile can be reinserted for iteration until the desired result is achieved.

Notes

  • Iterate requires a DeviceLink license.
  • The test chart must match the color space of the source profile. 
  • Out-of-gamut colors of the original color space can only be improved to a limited extent. 
  • In proofing situations, the gamut of the target color space ought to be larger than that of the source color space, which makes iteration particularly interesting for DeviceLink profiles in proofing applications.
  • Iterations cannot be repeated arbitrarily due to fluctuations in print output, print material and the reproducibility of measuring instruments. More than 2-3 iterations are usually not necessary and not recommended.
  • Only DeviceLink profiles whose source and target profiles are available and referenced in the DeviceLink profile can be iterated. A warning is issued if the required source and target profiles are missing.
  • Third-party DeviceLinks that reference the used source and target profiles can also be iterated.
  • DeviceLinks that use color Exceptions and perceptive rendering options (such as conversion and separation profiles) should not be iterated. Optimization allows the target values to be reached more accurately, which can result in a loss of channel purity. Perceptive rendering intents require an interpretation of the measurement data, which can lead to slight shifts during iteration.
  • With a DeviceLink and a Multicolor license Multicolor DeviceLinks can be iterated, too.

Procedure

Procedure

Procedure

  1. Select Iterate in the sidebar or DeviceLink Iteration in the Navigation menu.
  2. Select the DeviceLink profile that you would like to iterate from the drop-down menu. Make sure that both the source and target profiles used in the DeviceLink are available in the ICC profile folder of your operating system, as CoPrA needs those to calculate the iterated profile. 
  3. Convert the test chart to be used for iteration with the DeviceLink profile and print it on the printer using the same settings as for the profiling test chart for this printer. The test chart can be converted using CoPrA’s Image Conversion tool.
    
Note: Use a test chart that contains the colors you would like to optimize. Typically, test charts with few color patches will suffice, but those patches must reflect the colors to be optimized. Therefore, using large profiling test charts is not required. Instead of using large test charts, use charts that can also be used to update profiles (see ColorAnt/Custom Chart tool). The color space of the test chart must correspond to the color space of the source profile of the DeviceLink.
  4. Measure the printed test chart in ColorAnt, save the measurement data and open it in CoPrA’s Iterate tool, either via drag-and-drop or via the Load button. Alternatively, click Measure and measure the test chart with CoPrA’s integrated Measure Tool.
  5. CoPrA suggests a profile name if the source and target profiles are available and the measurement data has been loaded. Settings cannot be selected for profile creation.
  6. Click Save to calculate the new DeviceLink profile and save it in the ICC profile folder.
 Note: The newly created DeviceLink will have a more accurate color rendering for most in-gamut colors compared to the original DeviceLink profile. You can now use it in exactly the same way as the original one or use it for further iterations.
  7. If you would like to further optimize the DeviceLink, proceed as described above. However, select the previously iterated DeviceLink instead of the original one. Now convert the original test chart with the iterated DeviceLink (do not take the already converted test chart from point 3!) and use the measurement data of this printout to calculate a further optimized DeviceLink profile.

Verifying the optimization

Verifying the optimization

ColorAnt can be used to verify a successful optimization. First create a “Lab Reference” to compare the measured values of the printouts to the values of the DeviceLinks. Use the ICC Transformation tool to create the Lab reference values by using the device values of the original test chart and the source profile and rendering intent of the DeviceLink. These Lab reference values now serve as comparison values after each application of the iterated DeviceLinks on your test chart. Compare the measurements of the iteration with the “Lab Reference” using the Compare tool in ColorAnt. 

You will notice that in-gamut colors of the iterated DeviceLink are closer to the Lab reference than those of the original DeviceLink.