1. Definition
CMS (Camera Monitor System), commonly referred to in the industry as an electronic rearview mirror, uses a camera + monitor combination to replace traditional optical rearview mirrors. In this display mode, images captured by external cameras are processed and displayed on an in-cabin screen, while also integrating features such as blind-spot warnings and obstacle alerts.

CMS Directional Uniformity measures the luminance consistency of the same area on the CMS monitor across different viewing angles compared to the designed viewing angle. By measuring the luminance deviation at various viewing angles of the CMS monitor, it ensures that the displayed information remains clearly legible from any reasonable viewing angle during driving.

2. Test Method
Test KPIs:
According to regulatory standards such as ISO 16505 and GB 15084, the directional uniformity of CMS must meet the following requirements:
Standard directional uniformity range (±6° vertically and ±7° horizontally from the monitor's designed viewing angle): the luminance deviation between different viewing angles and the designed viewing angle must be <35%;
Extended directional uniformity range (an additional ±5° in both vertical and horizontal directions beyond the standard isotropic range): the luminance deviation between different viewing angles and the designed viewing angle must be <50%.

The formulas for calculating luminance deviation are as follows:
Standard isotropic range: $$\frac{\max\left\{ \left| L_i - L\left( \Theta_{\text{monitor}/D}, \Phi_{\text{monitor}/D} \right) \right| \right\}}{L\left( \Theta_{\text{monitor}/D}, \Phi_{\text{monitor}/D} \right)} < 35\%$$

Extended isotropic range:
$$\frac{\max\left\{ \left| L_{i'} - L\left( \Theta_{\text{monitor}/D}, \Phi_{\text{monitor}/D} \right) \right| \right\}}{L\left( \Theta_{\text{monitor}/D}, \Phi_{\text{monitor}/D} \right)} < 50\%$$

Measurement points at different viewing angles:
The standard isotropic range refers to the specific vertical range of 6° upward and 6° downward from the monitor's designed vertical viewing angle, as well as the specific horizontal range of 7° to the right and 7° to the left from the monitor's designed horizontal viewing angle.
The extended isotropic range refers to an additional 5° in both the vertical and horizontal directions beyond the standard isotropic range.

Test Procedure:
Display a 70% grayscale image on the monitor. Aim an imaging luminance meter equipped with a conoscope lens at the center of the monitor (at a distance of 3 mm) to capture the image. Use RIQA software to measure the luminance deviation between different viewing angles and the designed viewing angle. The test passes if the deviation is <35% for the standard range and <50% for the extended range.

Test Setup:
Camera side: Switch to a 70% gray chart. The optical axis of the DUT camera should be perpendicular to the chart and fill the monitor screen. The recommended light source color temperature is 6500K±1500K, with an illuminance of 800±80 lx (no supplemental lighting is needed if the screen is self-illuminating);
Monitor side: A dark environment with an illuminance below 10 lx is recommended. The conoscope lens must be positioned close to the monitor (at a distance of 3 mm).

Recommended Equipment:
Automated Chart Switching Mount Test System, Multi-CCT LED Supplemental Light Source (Visible and NIR), 70% Gray Chart (Optimal for Self-illuminating Screens), 2D Imaging Luminance Meter (Conoscope Lens), RIQA-CMS Image Quality Analysis Software, Mobile Mount for Monitor and Luminance Meter

Why is a conoscope lens required for measuring directional uniformity?
Because directional uniformity requires measuring luminance differences across varying viewing angles, which standard lenses cannot accommodate. A conoscope lens can measure a viewing angle range covering ±70° in a single capture, far exceeding the angular range required by the standard, thus fully meeting the testing needs. An imaging luminance meter equipped with a conoscope lens is the optimal solution for fast, accurate, and cost-effective viewing angle performance testing. The goniometer mentioned in the standard can also be used to measure directional uniformity, but it requires point-by-point measurements at each viewing angle, making the test procedure relatively cumbersome.

Result Analysis and Interpretation
a. Open the RIQA software, select the corresponding module (RIQA-CMS), and create a new project name or open an existing project. b. Fill in the relevant parameters of the DUT; c. Click “6 Directional Uniformity” to add the images to be tested. d. For “Analysis Method”, select the corresponding “Luminance File”. (TrueTest refers to the Konica Minolta X-Y luminance meter). e. Click “Start Analysis” to perform the test and obtain the results. The test passes if the luminance deviation is <35% for the standard range and <50% for the extended range.