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To examine the neutrality of the gray axis, we conduct a measurement using gray scales between ten and ninety per cent, which afterwards is set in relation to the actual white point. DeltaC indicates the difference in colourfulness and, with reference to achromatic colours, is adequate to DeltaE without brightness proportion. To reveal unpleasant variations towards different shades, we also try to determine the DeltaC range, which represents the value of the biggest distance vector between the colour samples in the a*-b*-level. Hereby, DeltaC range and DeltaC average relate to measured values that feature a brightness of more than one percent in relation to the white point.
Even in the factory setting, a display should be most neutral. At the highest, DeltaC is allowed to be at 4, while the range shall not exceed a value of 3. Otherwise distinct tints will appear. In terms of achromatic tones, the conscious perception level at a DeltaC value of 0.5 is far lower. To get a reliable result, it is a good idea to follow the guidelines of the UDACT (UGRA standard) which requires an average value of 1 at the maximum and a range of no more than 2. Naturally, this result should not be exceeded significantly, also and particularly in the calibrated state. Displays that are very neutral ex factory might show a minor decline after the calibration.
Evaluation criteria of our test reports: