Reference Measurement Files
Every target manufactured is different from the next. For best results calibration should be done with custom measurements that were recently taken.
OpenQualia Labels for Automatic Custom Measurements
Using custom measurements used to be cumbersome, but DT Nexus uses the OpenQualia Label Standard which greatly simplifies the process for the end user. No action by the end user is required in DT Nexus – if an OpenQualia Label is detected it is used by default (the user can still select another measurement if desired).
DT runs its own OpenQualia server where all measurements accessible via DT Nexus can be found.
Some targets are delivered with an OpenQualia Label (such as DT Nexus Transmissive Profiling and Validation Targets). Other targets are labeled with a serial number and can be found on the OpenQualia server using that serial number.
Note this requires an internet connection (as an OpenQualia Label is a link to a reference file) and the OpenQualia Label Host has to be working correctly.
Custom Measurements via Serial Number
DT Nexus automatically includes all factory measurements (in spectral format) made of GoldenThread FADGI 19264 targets, GoldenThread ISA OLT 1x, and DT NGT2 targets.
In the case of the ColorChecker SG the manufacturer does not provide the option to purchase with custom measurement of your specific target, and does not publish an official generic spectral reference. DT has included a generic ColorChecker SG reference file based on averaging spectral measurements of several copies over the last several years. However, there have been several variations of the ColorChecker SG as the manufacturer merged or was sold several times. This greatly limits the precision of our generic reference file and we strongly suggest using a custom measurement.
The user may also choose to make their own measurements with a tool like the i1 Pro or hire a company such as Digital Transitions to measure their target as a service; professional measurement benefits from the experience of the metrologist (ours is a PhD in Color Science with a specialization in metrology) and the quality of the spectrophotometer (our measurements are made with a Konica Minolta CM-2500c or similar lab-grade spectrophotometer with annual NIST-traceable calibration).
A professional measurement is only useful if the target is still in the same physical condition as at the time it was measured. Most targets are not cleanable, so any dirt or oil or other contaminants are hard to eliminate without changing the color of the patch. The patches of the DT NGT2 are encapsulated such that they are highly cleanable without altering the color.
Custom measurements must comport with the OpenQualia Measurement File Standard which is a specific flavor of the CGATs standard. Specifications for the OQ Measurement file format, and examples for each supported target can be found here. It is usually easiest to start with one of the example files, and update the information in the header and the spectral readings in the body. Spectral measurement files of this format can be placed in the following path:
~/Library/Application Support/Digital Transitions/DT Nexus/Reference
The User Library can be accessed in the Finder by holding the Option key while selecting the 'Go' dropdown menu.
DT Nexus tracks this folder while launched, so if you want to add a new profile you do not need to restart the software.
Order of Measurement Prioritization
DT Nexus selects the default profile presented for a given serial number based on the following order of preference: OpenQualia, Other Custom measurements, Factory, Generic. That is, if a custom reference file is available for your serial number (as determined by following the name template of the example OQM files) it will be the default; if there are more than one than the one that is alphabetically last will be the default.
This means you can simply add a “b” (or “c” etc) to the end of the filename so that it sorts lower and will be the default. If a Custom Reference is not available, but a Factory Reference is then it will be used; these are packaged inside the application and cannot be modified. Finally, if no Custom Reference is available the Generic Reference for that target will be used; this will limit the precision of profiling and validation – though this will only be readily apparent if you do independent validation.