With the desire to have fast profiling, low cost, and colour accuracy being a bit of an oxymoron, an alternative method is needed to increase the colour accuracy of faster, and cheaper, colourimeter probes.
This is performed by calibrating, or matching, a colourimeter based probe to a spectroradiometer on the same display.
In this way the colourimeter is accurately matched to the spectroradiometer for the specific display to be profiled, producing more accurate results.
There are two different methods available for probe matching - 4 Colour Matrix, and multi-point Volumetric Probe Matching.
Probe Matching Benefits
Using probe matching, the speed benefits of a colourimeter, and more importantly the lower-light reading capabilities, can be employed while simultaneously enjoying the greater accuracy of a spectroradiometer.
4 Colour Matrix
The 4 Colour Matrix probe matching method is the simplest, and most commonly used, process, but is limited in accuracy for displays that have a non-additive colour response, such as WOLEDs. For the majority of displays it is all that is required for accurate probe matching.
- Attach the first (colourimeter) probe, selecting standard probe parameters as required from Probe Options
(A None/Bypass/Default pre-set within the colourimeter should be used, not a display specific matrix pre-set)
- Select Configure from the Probe Matching option, and press New
- Enter a matrix name and press OK
(Use a name that includes the display and probe details)
- Place the probe on the patch window and press Measure All
(The patch window will cycle R, G, B and W patches, and save the probe/display matrix data)
- Change the probe to the second (spectro) probe, and repeat the process
(Spectro's do not use matrix pre-sets)
Note: the order the probes are measured in is not important, and you can measure the spectro first, with the colourimeter second.
- If using a separate patch window, not controlled via ColourSpace, use the RGBW << Measure buttons in-turn
(Each patch colour needs to be a value of 240 to match the ColourSpace generated patches)
- With the probe placed on a patch of the correct matching colour press the relevant << Measure button to take a measurement
(When White is measured the Luma value will be updated too)
- Alternatively, manually enter the xy values, remembering to record the Luma value when reading white
Regardless of the procedure used to take the probe measurements, the profile files are used in the same way.
- Select the spectro Reference Probe/Display Preset matrix from the Probe Matching lower drop-down menu
- Select the colourimeter Active Probe/Display Data matrix from the upper drop-down menu
- All colourimeter measurements will now be corrected to match the spectro using Probe Matching when the Active option is ticked
Multi-point Volumetric Probe Matching is unique to ColourSpace and LightSpace, and as the name suggests uses more than the 4 colour measurements of the above 4 Colour Matrix method. This is aimed at displays that have a non-additive colour response, such as WOLEDs, where the addition of the white pixel breaks the expected additive of the display.
The fundamental difference with Volumetric Probe Matching is that the entire displays colour volume is profiled to perform the match, not just 4 'bright' patches.
- For Volumetric Probe Matching a profile really needs to be cube based
(Volumetric Probe Matching will work best with uniform profiles, not random ones, and additional uniform points can be added near black to help improve accuracy with less sensitive probes)
- Best results will be attained when the display peak white is set to be close to the target peak white
(For example, 100 nits for SDR calibration)
- Profile the display with each probe in-turn as normal, with no probe selection with the Probe Matching option
(Use a None/Bypass/Default pre-set within the colourimeter, not a display specific matrix pre-set)
- After profiling both probes, open the Space Management library, and use Generate BPD to convert the profiles into Probe Matching files
The probe matching files can now be selected within the Probe Matching option, exactly as for 4 colour matrix probe matching