HLG Paper White Calculator

Calculate HLG diffuse white (paper white) and extended range (109%) luminance based on display peak brightness and viewing environment.

1. Viewing Environment

Room Lux & Reflectivity Ambient Nits Directly

Room Illuminance (Lux) ? Typical Values (ITU-R BT.2408-7 Table 5): - Office (Sunny Day): 130 Lux - Office (Cloudy Day): 75 Lux - Edit Suite: 50 Lux - Grading Suite: 25 Lux - Prod. Gallery/Dark Grading: 3 Lux (Perpendicular to the monitor surface)

Surround Reflectivity (0.0 to 1.0) ? Common Reflectivity Estimates: - Fresh Matte White Wall: ~0.8 to 0.9 - Light Grey / Off-White Wall: ~0.6 to 0.7 - ITU-R BT.2408-7 Table 5 assumes ~0.6 for "light-coloured walls". - 18% Grey Card: 0.18 - Darker surfaces have lower values.

Ambient Surround Luminance (cd/m² or nits) ? Typical Values (ITU-R BT.2408-7 Table 5): - Office (Sunny Day): 25 cd/m² - Office (Cloudy Day): 15 cd/m² - Edit Suite: 10 cd/m² - Grading Suite: 5 cd/m² - Prod. Gallery/Dark Grading: 0.5 cd/m² (Perpendicular to the monitor surface)

2. Display

Display Peak Luminance (L_W for 100% HLG Signal, cd/m²) ? Enter the luminance your display produces for a 100% HLG signal. This is the L_W used for gamma calculations. For EBU R 167 "ext" modes (e.g., "1000ext"), this would be the nominal L_W (e.g., 1000), not the extended peak. Sources for Peak Luminance - Physical Measurement Device - Reviews/Tests - Windows HDR Calibration Tool - Display EDID / CTA-861 HDR Metadata - Manufacturer Specs (Website/Box)

Advanced Settings

HLG Signal Level for Paper White (%) ? The HLG signal level representing diffuse white. ITU-R BT.2408-7 recommends 75%. Adjusting this changes the target brightness for diffuse white.

Default and ITU recommendation is 75%.

Black Level Luminance (L_B, cd/m²) ? The measured or specified black level of your display. Common examples: - Dolby Cinema P3 PQ: 0.0001 cd/m² - High-end OLED: ~0.0005 to 0.001 cd/m² - Good LCD with FALD: ~0.005 to 0.02 cd/m² - Typical LCD: ~0.05 to 0.1 cd/m² ITU-R BT.2100 suggests using PLUGE (BT.814) to determine L_B. Setting to 0 effectively disables black level lift.

Enter display's minimum black luminance. Default 0.0001 (Dolby Cinema). 0 to disable.

Approximate QD-OLED Ambient Black Level (Experimental) ? When checked, this approximates a useful black level approximation for some QD-OLED displays using the formula: Room Lux * (nit black level raise per lx - bias) with a raise of 0.0022 nits / lx and a bias of 0.0002 nits / lx. Reasoning: QD-OLED: 0.0022 nits ambient black level raise / lx minus 0.0002 nits / lx for other displays, to compensate for bias, as I don't think ambient black level raise has been used in the ITU formulas. This will override and disable the manual L_B input. I do not know if this adjustment will result in more accurate results. This option is only active when "Room Lux & Reflectivity" is selected for viewing environment.

Force Extended Gamma Formula Always ? ITU-R BT.2100-3 Note 5f specifies a piecewise function for System Gamma based on Display Peak Luminance: one formula for the 400-2000 cd/m² range and an 'extended' formula for values outside this range. Enabling this option forces the continuous 'extended' formula (γ = 1.2 * κ^(log2(Lw/1000))) to be used across all peak luminance values. This will deviate from the strict ITU standard for the 400-2000 cd/m² range but provides a smoother, continuous curve.

Show Calculated 109% HLG Signal Luminance ? Calculates and displays the luminance produced by a 109% HLG signal level, based on the current L_W (for 100% signal) and system gamma. This utilizes the "super-white" headroom defined in EBU R 103. The 109% signal is (1019-64)/(940-64) for 10-bit narrow range.

Results

Using HLG Paper White Signal
Calculated Ambient Surround Luminance (L_amb)
Black Level Lift (β)
Peak L_W Adjusted Gamma (Base)
Surround L_S Gamma Offset Comp.
Effective System Gamma
Luminance at 109% HLG Signal
Recommended HLG Paper White (75% HLG)

Formulas based on ITU-R BT.2100, BT.2390, and BT.2408 & EBU R 167.

This is a simplified tool for educational and estimation purposes. View on GitHub