Dynamic range
Not merely a brighter picture but a complete system: BT.2100, reference white, PQ/HLG, wide colour, mastering displays, tone/gamut mapping, metadata and delivery control.
HDR expands display-light range and colour volume while keeping diffuse objects at a sensible level. The core idea is not to raise the whole image but to leave room between ordinary white and very bright highlights.
Quick reference
Two HDR systems: PQ and HLG; BT.2020/D65 colorimetry.
Diffuse/graphics white in ITU production guidance.
ST 2084; mathematical ceiling 10,000 cd/m².
75% HLG = reference white; ≈203 cd/m² on a nominal 1000-nit display.
HDR SYSTEM MAP
In professional video, HDR describes a coordinated capture/rendering/display chain. ITU-R BT.2100 defines two HDR systems, PQ and HLG, and uses BT.2020 colorimetry. A file must still signal transfer characteristics, matrix, range and other states correctly. An 'HDR' label alone is therefore not enough for diagnosis.
BT.2100 combines UHD/HDR colorimetry, transfer-system parameters and digital representation. Its primaries correspond to BT.2020 and its white point is D65. That does not mean a real display must physically cover the entire Rec.2020 triangle; mastering/display gamut can be smaller and the output pipeline must handle unavailable colours gracefully.
In current ITU production practice, HDR Reference White is the nominal signal level from a 100% reflectance white card that produces 203 cd/m² on a PQ display or an HLG display with a nominal 1000 cd/m² peak. It is a reference for diffuse white and graphics white, not the HDR ceiling. That is why ordinary faces, walls and white shirts should not automatically jump to 1000 nits.
Most of the picture can retain a familiar tonal hierarchy while extra HDR headroom is used for glints, fire, the sun, practical lights and other objects that should feel brighter than a white diffuse surface. This preserves natural visual hierarchy instead of turning HDR into an exhausting bright version of SDR.
PQ/ST 2084 is display-referred absolute-luminance encoding: a signal value relates to a defined luminance. HLG/STD-B67 is a more scene-oriented relative system with a hybrid OETF and display system gamma. A PQ master and an HLG broadcast signal are therefore not two names for the same gamma preset.
BT.2100 uses BT.2020 colorimetry, so an output may differ from SDR both in luminance and in available saturation at different brightness levels. A 2D gamut triangle shows chromaticity only. The real HDR problem is three-dimensional colour volume: gamut × luminance × display limits.
1000, 2000 or 4000 cd/m² in a mastering-display description refers to an upper capability of the reference display/workflow, not a requirement for every frame to use that level. Content peak, mastering peak, HDR Reference White and average picture brightness are four different concepts.
Final evaluation needs a monitor path that receives the target HDR signal correctly and can actually reproduce the intended range. A GUI Viewer is useful for work but does not replace a calibrated HDR reference display. Scopes also need the right scale: 0–1023 code values, IRE-like scales and nits answer different questions.
White titles and interface elements are not specular highlights. ITU production guidance aligns Graphics White with HDR Reference White. If a title is encoded much brighter without reason, it can dominate faces and the scene and may behave poorly during HDR-to-SDR conversion.
PQ-based distribution ecosystems can carry mastering/display metadata and content-light metadata, while some dynamic-HDR systems add scene/shot guidance. Such data can assist downstream display mapping but cannot replace a correct grade, output transform and signal-state control.
Moving to SDR requires simultaneous decisions about luminance compression, highlight hierarchy, possible gamut reduction and graphics behaviour. Good conversion preserves intent: important detail and relative relationships remain readable. Simple gain or clipping destroys the very information HDR was meant to preserve.
Identify every clip's source state, choose a wide scene-referred timeline/working space, define a specific HDR output such as BT.2100 ST2084/PQ or BT.2100 HLG, and only then evaluate tone/gamut mapping. In managed RCM, output rendering is handled by the system transform; in a manual CST workflow, make sure CST does not duplicate a project-level transform. For HDR10-like delivery, separately verify mastering metadata and encoder/container signalling.
Verify five things independently: target primaries/colorimetry, transfer (PQ or HLG), signal range, bit depth/chroma format, and mastering/stream metadata. Then inspect the actual render with scopes and the target display path. A correct-looking picture in one window does not prove the file is correct.
HDR is built around signal states and display intent. If you cannot name the target transfer, target colorimetry, reference white and monitoring path, the workflow is not fully defined yet.
Technical definitions are anchored to standards bodies and primary specifications wherever that distinction matters.
Current Recommendation covering PQ, HLG, BT.2020 colorimetry and digital representation.
Current operational guidance for HDR Reference White, monitoring, graphics and HDR/SDR conversion.
Background and practical detail for PQ/HLG, display mapping and production.
Colour Management, CST, HDR grading, scopes and delivery settings.
