REVIEW: NEC LCD2470WNX Part 8

Colour deviation and calibration

As well as measuring the colour spaces, we checked exactly how precisely the MultiSync LCD2470WNX displays the die reproducible colours. To do this, we made three comparisons: First, we compared the sRGB colour space with the factory settings of the LCD.

Secondly, we compared the sRGB mode of the monitor with the sRGB standard profile and lastly, we compared our calibrated settings with the sRGB standard profile. The first two comparisons should show how well the LCD is suited to sRGB display without calibration, since most users do not possess the necessary calibration hardware.

Since the gamma value and white point of the factory settings are closer to sRGB than those of sRGB mode, we will only include the results of the latter here. The values of the sRGb mode, at gamma 2.09 and 6700K, are somewhat poorer, and the grey values are further off target as a result. However, the user can still work well in sRGB using the sRGB mode.

Colour deviation is given in deltaE 94; we measured numerous grey levels, the primary (RGB) basic colours and the secondary basic (CMY) colours. a deltaE value of 1 represents the smallest colour deviation that can be perceived by the human eye.
Most people notice a deviation in colour from a value of 3. However, our eyes are more sensitive to green and grey tones. The average deviation should be under 3 dE land the maximum should be under 10 dE. Up to this value, colours are still sufficiently similar to each other.

Comparison of factory settings to sRGB standard

Factory setting	Manufacturer	Measured
White point / Kelvin	n/a	6600
Brightness / cd/m²	n/a	477
Black point / cd/m²	n/a	0,40
Gamma / average	n/a	2,15
Contrast / x:1	n/a	1191

Despite the good values we measured, some colour faults can be observed for some grey tones. The deltaE values measured are all under the critical value of 10 dE, and with an average deviation of 1.6 dE, the values are even nearly in the green or excellent zone. We later checked how well the NEC monitor performs in terms of colour fidelity after calibration.

Comparison of calibrated profile with sRGB standard

Calibrated	Goal	Measured
White point / Kelvin	6500	6500
Brightness / cd/m²	140	141
Black point / cd/m²	0,00	0,10
Gamma / average	sRGB (~2,2)	2,17
Contrast / x:1	max.	1404

The last diagram shows the disadvantage of software calibration. In order to bring the greyscale closer to the sRGB gamma, the calibration software must change the graphics card output. This means that the primary colours deviate further than before calibration. However, since this affects the intensive colour tones at any one time, this compromise is acceptable.

With a little more effort, a better calibration result could certainly be achieved. The measured black point is outstanding and the resultant contrast ratio of up to 1400:1 is significantly higher than that advertised by the manufacturer.

Representation of the RGB correction curve after calibration. The closer the three coloured lines are to the 45° axis, the fewer colours have to be abandoned for correct calibration of the graphics card and the more complete the colour gradients remain. Click for enlarged view.

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