Test Method:
Display the gray scale test chart on the monitor, measure the luminance of each gray patch displayed on the monitor, calculate the lightness of each gray patch according to Formula (1), and then calculate the lightness difference between adjacent gray patches according to Formula (2). The requirement is that the lightness difference $\Delta L^*$ for at least 8 adjacent gray patches on the chart must be ≥ 3.

Conversion from luminance to lightness:

\[ L_i^* = \begin{cases} 116 \times \left( \dfrac{Y_i}{Y_{12}} \right)^{1/3} - 16, & \dfrac{Y_i}{Y_{12}} > 0.008856 \\ 903.3 \times \left( \dfrac{Y_i}{Y_{12}} \right)^{1/3}, & \dfrac{Y_i}{Y_{12}} \leq 0.008856 \end{cases} \tag{1} \]

Lightness difference: $\Delta L^* = L_{i+1}^* - L_i^* \tag{2} $

Environment Setup:

Camera Side:
The illuminance on the test chart is 500 lx, and the light source color temperature is 6500 K ± 1500 K.

Monitor Side: The ambient illuminance shall not exceed 10 lx.

Recommended Equipment:
Automated Chart Switching Bracket Test System, Multi-CCT LED Fill Light Source (Visible and Near-Infrared), Reflective 12-Step Gray Scale Test Chart, 2D Imaging Luminance Meter, RIQA-CMS Image Quality Analysis Software, Monitor and Luminance Meter Mobile Stand

Test Chart:

The gray scale reproduction chart must include 12 gray patches with different tone densities; the density values Di must conform to the defined values for a low contrast ratio of 20:1 as specified in ISO 14524:2009. The background of the patches must be covered with a neutral gray having a density value Di of 0.54 ± 0.05. Reflective and transmissive charts with Lambertian characteristics may be used.

Test Procedure:
a) Ensure that the gray patches of the gray scale chart are visible at the defined center of the monitor;
b) Adjust the distance between the camera under test and the chart so that the monitor under test displays the chart patches with at least 50×50 pixels (for Class IV CMS, the display pixels of the chart patches may be reduced);
c) Adjust the color temperature of the light source on the camera side to 6500 K ± 1500 K, and the illuminance on the chart to 500 lx; the ambient illuminance on the monitor side should be less than 10 lx;
d) Use a luminance testing device (imaging luminance meter) perpendicular to the monitor to capture the test image;
e) Use the RIQA-CMS image quality analysis software to analyze the test image and obtain the lightness difference data of adjacent gray patches. If the number of distinguishable gray levels is greater than or equal to 8, it meets the requirements of the standard (GB 15084).

RIQA displays the lightness variation curve from the 1st to the 12th patch, the lightness difference between adjacent gray level patches, and the specific data for the number of distinguishable gray levels.