Instrument Correlation
Colorimeters have sensor metamerism due to their design. The manufacturer tries to reduce this by using prefabricated correction matrices. With the i1 Display Pro, for example, you can choose between 8 corrections for different monitor technologies, with the Spyder 5 between 4 global corrections for different backlights, with basICColor DISCUS between 30 (more are reloadable) corrections for monitor models. basICColor display 6 Pro allows you to optimize each measurement device for each individual monitor to achieve optimal results that are as close as possible to a reference device.
The table below is showing interesting data documented by basICColor (Germany) engineers, who made a state-of-art display calibration application with the correlation utility to match reference-instrument readings.
| Instrument | S/N, cond. | raw data | correlated | |||
| ∆E Avg. | ∆E Max | ∆E Avg | ∆E Max | |||
| REFERENCE |
Myiro-1 |
10001018, Spectral |
— | — | — | — |
| 1 |
i1Pro II |
1000969, Spectral |
0.41 |
0.87 |
0.30 |
0.72 |
| 2 |
i1Pro |
100201, Spectral |
2.61 |
5.26 |
0.38 |
0.95 |
| 3 |
i1Studio |
Spectral |
6.54 |
10.78 |
0.27 |
0.63 |
| 4 |
i1Display Pro |
OE-14.A-02.104248.06, White LED |
2.01 |
6.39 |
0.30 |
0.91 |
| 5 |
Spyder 5 |
50035848, White LED |
3.12 |
5.86 |
0.25 |
0.46 |
| 6 |
Spyder X |
60076575, Wide LED |
1.70 |
5.59 |
0.56 |
1.60 |
| 7 |
Eizo Sensor |
Eizo CG246 |
3.17 |
7.96 |
0.48 |
1.00 |
| 8 |
basICColor DISCUS |
084011385431F, |
4.51 |
13.66 |
0.30 |
0.54 |
Correlation - basic pripciples?
The process of correlation needs to measure the same set of color patches with two or more different instruments on a given display. It is valid only for particular monitor/instrument pair. Every single monitor and every single instrument par requires a separate procedure that finally produces a unique correction matrix. Correlation is based on 17 color samples.
Correlation ensures that the measurements of different sensors are (as far as possible) comparable to the measurements of a reference measuring device and to each other. A perfect match cannot be guaranteed due to the different designs.
How to start?
The user has to select a Reference Instrument. This is important to pick the instrument that is high-quality and can be "travel" across all locations.
Why differences?
There is a couple of reasons that explain the differences between Instruments. Some of them offer various user-selected pre-setting that can more or less compensate for issues. In this case, the user has to understand what to select and why...
- The operator doesn't understand the settings of the Instrument
- Instrument/sensor design. Colorimeters used different tri-stimulus values
- Non-perfectly human correlated 2° Standard Observer definition - used for calculations
The color matching functions are the tristimulus values of the equal-energy spectrum as a function of wavelength. This should reflect how human aye can see the color - but it is inaccurate - This definition has been created in the year... 1931, modified in 1964. Vendors are adopting calculations to get better human-correlated results when calibration/profiling is applied to the monitor. For example, DISCUS by basICColor offers the best XYZ match to the human eye but the numbers will be very different. Monitor calibrated with this instrument will operate better than most others... Also, some hi-end calibrators used in the cinema Industry are using not an official 2° Observer definition to get perfect calibration for high-demanding users.
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