HDR transfer function
The absolute HDR EOTF without myths: ST 2084 formula, the 10,000 cd/m² design range, 203-nit reference white, perceptual quantisation, mastering/display mapping and Resolve workflow.
PQ does not encode generic brightness percentages; it encodes absolute display luminance. A signal value has meaning inside ST 2084/PQ: 1.0 maps to the mathematical ceiling of 10,000 cd/m² even though real masters normally use a much lower peak.
Quick reference
Signal value → defined display luminance.
Not a mandatory mastering peak.
Key ST 2084 exponents.
Nominal diffuse/reference white in ITU HDR production.
SMPTE ST 2084 · PQ
ST 2084 defines the relationship between a nonlinear value N/E′ and mastering/reference-display luminance. That is fundamentally different from relative gamma: the same PQ value is intended to represent the same absolute luminance before display mapping intervenes. This makes PQ especially useful for controlled mastering intent.
The reference EOTF uses five constants: m1=2610/16384, m2=(2523/4096)×128, c1=3424/4096, c2=(2413/4096)×32, and c3=(2392/4096)×32. For normalized input E′, first compute p=E′^(1/m2), then L=10000×(max(p−c1,0)/(c2−c3·p))^(1/m1). L is expressed in cd/m².
PQ ends at 10,000 cd/m², but ST 2084 does not require a display or master with that peak. The system provides one absolute scale for different target peaks. A 1000-, 2000- or 4000-nit mastering display uses only part of the mathematical range, and downstream devices perform display mapping when necessary.
Human sensitivity to luminance changes depends strongly on adaptation level. PQ is designed as a perceptually efficient quantizer, allocating code steps so quantisation remains less visible across a very large range. Thus 50% PQ does not mean 5000 nits and is not 'half brightness'.
ITU HDR production guidance uses 203 cd/m² as nominal HDR Reference White/diffuse white. This creates a useful bridge between ordinary diffuse objects and bright HDR highlights. In PQ mastering, 203 nits has a specific absolute code-value location, unlike a relative white convention in a conventional SDR gamma workflow.
ST 2084 is a transfer/EOTF. Primaries, white point, YCbCr matrix and range are separate properties. In BT.2100, PQ normally appears with BT.2020 colorimetry, but 'PQ' and 'Rec.2020' are not interchangeable names. A wrong matrix or gamut interpretation stays wrong even with a perfect PQ curve.
A camera does not have to record scene light directly into ST 2084. In a production pipeline, the source is first brought into a scene-referred working state; creative grading and the output/rendering transform then convert the scene to display-referred PQ. This is where the relationship between diffuse white, skin, highlights and display peak is created.
If a master contains luminance beyond a television's capability, the device needs an EETF/display-mapping step: preserve important tonal hierarchy and smoothly redistribute the upper range instead of hard clipping. This downstream rendering does not change the fact that the source PQ master has absolute-luminance semantics.
Static HDR ecosystems often add mastering-display characteristics and content-light information; dynamic systems can carry additional guidance. The PQ curve itself does not contain creative instructions for every display. Metadata can assist mapping, while luminance encoding remains ST 2084.
A nit scale is especially useful for PQ because it shows where diffuse white and highlights sit in the absolute domain. Code values without transfer context are less intuitive. Do not confuse signal peak with mastering-display peak, and do not judge an entire scene from one single-frame maximum.
In RCM, define the correct scene-referred timeline/working state and a BT.2100 ST2084/PQ target output. In a manual CST workflow, an input CST normalises the source while an output CST/DRT converts the working state into PQ; the same technical transform must not exist both in Project Settings and in nodes. Use HDR tools/scopes inside that deliberate target context.
For PQ delivery, separately confirm BT.2020/target colorimetry, ST2084 transfer signalling, narrow/full range, bit depth and codec/container metadata. An error in any one of these fields can make a correct grade look wrong on another player/display.
A useful habit for PQ is to think in cd/m² rather than abstract percentages. White, highlight, mastering peak and display limit then stop collapsing into one number.
Technical definitions are anchored to standards bodies and primary specifications wherever that distinction matters.
Primary specification of the PQ EOTF/inverse EOTF and digital representations.
Current ITU Recommendation for PQ/HLG HDR television.
EETF/display mapping and practical HDR context.
203 cd/m² reference white, monitoring and production practices.
HDR colour management, scopes, CST and output workflows.
