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IEC TS 62977-3-1:2019 — Electronic Display Viewing Direction Dependence Based on Colour Difference
Evaluation of optical performance and angular colour shift for modern display technologies
Introduction to IEC TS 62977-3-1:2019
IEC TS 62977-3-1:2019, part of the IEC 62977 series on electronic displays, provides a standardized methodology for evaluating the viewing direction dependence of colour displays based on colour difference metrics. Unlike traditional approaches that rely solely on contrast ratio (CR > 10:1) to define viewing angle, this technical specification introduces a perceptually relevant metric that combines luminance degradation with chromaticity deviation to assess display quality from off-normal viewing directions.
The standard applies to colour matrix displays based on transmissive technologies (LCD), emissive technologies (OLED, PDP), and emerging display types including micro-LED and quantum-dot displays. It addresses the fundamental challenge that display colour appearance changes with viewing angle — a phenomenon particularly pronounced in liquid crystal displays where the inherent birefringence creates angle-dependent phase retardation.
Research cited in the standard demonstrates that correlation between metric value and visual assessment increases significantly when colour differences are included. A contrast-ratio-only approach fails to capture colour shift artifacts readily perceived by viewers, especially for large-format televisions and mobile devices viewed from oblique angles.
Measurement Methodology and Colour Difference Calculation
The measurement procedure requires a light measuring device (LMD) — either a luminance meter, colorimeter, or spectroradiometer — positioned on a goniometric stage. The standard defines a polar coordinate system with polar angle θ (0° to 90° from normal) and azimuthal angle φ (0° to 360°), enabling comprehensive characterization of angular emission profile.
| Measurement Parameter | Specification | Notes |
|---|---|---|
| LMD Type | Spectroradiometer preferred | Mandatory for narrow-spectrum sources (laser, QD, narrow-peak OLED) |
| Spectral Range | 380 nm – 780 nm | Minimum; extended range for wider gamut displays |
| Bandwidth | ≤ 5 nm (sharp peaks); ≤ 10 nm (broadband) | Narrower bandwidth improves accuracy for laser displays |
| Angular Resolution | ≤ 1° for polar angle | Critical for displays with narrow viewing cones |
| Test Signal | 4% window pattern at 100% white | Reduces stray light and APL effects |
| Measurement Area | ≥ 100 pixels per dimension | Ensures statistically significant chromaticity sampling |
| Environmental Conditions | Dark room, 23 °C ± 2 °C | No ambient light interference |
The core evaluation method is the CIEDE2000 colour difference formula (ΔE00), which quantifies perceived difference between on-axis (reference) colour and off-axis (measured) colour. The standard specifies measurement at multiple angular positions: for TV applications, polar angles of 0°, 15°, 30°, 45°, and 60°; for mobile displays, additional measurements at 75° and 80°.
Engineers should note that CIEDE2000 incorporates parametric weighting factors (kL, kC, kH) that can significantly affect results. The standard specifies kL = 1, kC = 1, kH = 1 for the reference condition. Always report which parametric factors were used.
Evaluation Criteria and Interpretation
The standard defines thresholds for acceptable colour difference: ΔE00 below 1.0 is imperceptible, 1.0 to 3.0 is acceptable, 3.0 to 6.0 represents noticeable colour shift, and above 6.0 indicates significant colour distortion. These thresholds, combined with the angular position at which they are exceeded, define the display’s useful viewing direction range.
Half-Luminance Angle vs. Colour Difference
Informative annexes provide additional parameters including half-luminance angle and gamma distortion from viewing direction. These reveal that a display may have excellent half-luminance angle (> 80°) while exhibiting unacceptable colour shift at much smaller angles (e.g., 30°), particularly in IPS-LCD panels where off-axis gamma distortion causes grey-scale inversion.
For display manufacturers, optimizing LC mode (e.g., from TN to IPS or VA) and implementing colour shift compensation algorithms in the driver IC can significantly improve colour-difference-based viewing angle. Advanced approaches include pixel-level optical compensation films, multi-domain vertical alignment (MVA), and patterned retarders.
Engineering Design Insights for Display Angular Performance
Improving viewing angle requires a multi-layered approach. At the LC cell level, liquid crystal material choice directly affects angular dependence of retardation. High-birefringence (Δn) materials enable faster switching but typically exhibit stronger viewing angle dependence. Cell gap (d) optimization involves trade-off between optical efficiency and angular stability.
Optical compensation films represent the most effective passive approach. Biaxial compensation films with negative C-plate characteristics reduce off-axis light leakage in the dark state. For VA-mode LCDs, A-plate + C-plate compensator stacks are widely used; for IPS-mode, positive A-plate with negative C-plate combinations are typical.
Active compensation through local dimming and colour shift algorithms is gaining traction in premium displays. By analyzing viewing direction and applying pre-distortion to RGB sub-pixel drive levels, colour shift can be partially compensated. The standard provides the measurement framework to validate such systems.
A critical pitfall is the trade-off between brightness uniformity and colour uniformity. Highly directional backlight systems (e.g., collimated quantum-dot enhancement films) improve on-axis brightness by up to 40% but narrow the angular distribution, creating a “hotspot” effect where colour shift increases rapidly beyond 20°. Careful balancing is essential.
Frequently Asked Questions
Q1: How does IEC TS 62977-3-1 differ from traditional viewing angle measurement (contrast ratio > 10:1)?
A: The traditional method only considers luminance-based contrast ratio, failing to capture colour shift. IEC TS 62977-3-1 uses CIEDE2000 colour difference, combining luminance degradation and chromaticity deviation into a single perceptually relevant metric that correlates significantly better with human visual assessment.
A: The traditional method only considers luminance-based contrast ratio, failing to capture colour shift. IEC TS 62977-3-1 uses CIEDE2000 colour difference, combining luminance degradation and chromaticity deviation into a single perceptually relevant metric that correlates significantly better with human visual assessment.
Q2: What are typical ΔE00 values for current display technologies at 45°?
A: Premium OLED displays achieve ΔE00 < 3.0 at 45° due to Lambertian emission. High-end IPS-LCDs with compensation films achieve 3.0-5.0. Standard VA-LCDs may exceed 8.0 due to gamma distortion. TN-mode LCDs often exceed 10.0 beyond 30°.
A: Premium OLED displays achieve ΔE00 < 3.0 at 45° due to Lambertian emission. High-end IPS-LCDs with compensation films achieve 3.0-5.0. Standard VA-LCDs may exceed 8.0 due to gamma distortion. TN-mode LCDs often exceed 10.0 beyond 30°.
Q3: What equipment is needed for compliant measurements?
A: A goniometric stage with ≤ 1° precision; a spectroradiometer with ≤ 5 nm bandwidth (for narrow-peak sources); a dark-room environment at 23 °C ± 2 °C; and test signal generation for 4% window patterns and full-field signals.
A: A goniometric stage with ≤ 1° precision; a spectroradiometer with ≤ 5 nm bandwidth (for narrow-peak sources); a dark-room environment at 23 °C ± 2 °C; and test signal generation for 4% window patterns and full-field signals.
Q4: Can this metric apply to non-emissive displays like reflective e-paper?
A: The standard’s scope is limited to emissive and transmissive displays. For reflective displays, dark-room conditions are not representative. However, the colour difference methodology itself is technology-agnostic and could be adapted with appropriate ambient illumination conditions.
A: The standard’s scope is limited to emissive and transmissive displays. For reflective displays, dark-room conditions are not representative. However, the colour difference methodology itself is technology-agnostic and could be adapted with appropriate ambient illumination conditions.
