Tier: SMT200: Systems
Related: SMT100: Core Principles · SMT300: Research

SMT207: Exposure & Reference Display Anchors

Exposure defines structural boundaries. Reference display evaluation determines how those boundaries are judged.

This document outlines the non-negotiable anchors used in a DWG scene-referred HDR + SDR workflow.

1. Reference Anchors (Non-Negotiable)

Middle Grey (Scene-Referred)

  • 18% grey = L = 0.18 (linear scene light)
  • Rec.709 reference display: ~41–43 IRE
  • HDR PQ (1000 nit target): ~100 nits

If grey is wrong, everything downstream is wrong.

Structural Note
In scene-referred space, exposure behaves linearly:

Y = k \cdot L

Where:
L = scene radiance
k = exposure gain
Y = output signal

Exposure scaling is linear in scene space. It is not perceptual.

2. Skin Tone Anchors (Before Creative)

Skin is the narrative anchor. These ranges are structural starting points, not aesthetic ceilings.

Lighting Context SDR (IRE) HDR (1000 nit)
Dark skin key 35–45 60–120 nits
Medium skin 45–60 120–220 nits
Light skin 55–70 200–350 nits

Live: Reference Display Anchor Explorer

Drag the exposure slider. Watch where skin tones, middle grey, and highlights land across SDR and HDR simultaneously. The structure is the same. The rendering is not.

3. Highlight Philosophy

Highlight handling defines fatigue, not brightness.

SDR (Rec.709 — 100 nit)

  • Legal ceiling: 100 IRE
  • Practical ceiling: 95–98 IRE
  • Texture often disappears above ~92 IRE on consumer displays

HDR (PQ — 1000 nit master)

  • Diffuse white ≈ 200 nits
  • Highlight detail zone: 200–600 nits
  • Specular highlights: 600–1000 nits
  • If everything lives above 400 nits → viewer fatigue

HDR is about separation, not brightness.

4. Shadow Discipline

  • SDR black: 0 IRE legal, protect 2–4 IRE for stability
  • HDR near black: do not decorate the noise floor
  • If noise is visible before emotion is visible → exposure was wrong

Scene-referred rule:
Lift with structure, not with gain.

5. Reference Display Order of Operations

  1. Balance in DWG (scene-referred)
  2. Confirm grey anchor
  3. Confirm skin
  4. Evaluate highlight distribution
  5. Then apply creative look
  6. If delivering HDR + SDR: trim to SDR (PQ pipelines only — see below)

Never design look in SDR first if HDR is master.

PQ vs HLG: Not the Same Trim

PQ is an absolute system. Code values map directly to nit values via the ST 2084 curve. Diffuse white sits at approximately 203 nits (around 58% of the PQ signal range). An SDR trim pass is required: no automatic relationship exists between the PQ master and an SDR display. ST 2086 mastering metadata is required, and the trim pass sets the rendering intent for downstream mapping.

HLG is a relative system. The OOTF adapts dynamically to the peak luminance of the target display via a system gamma parameter. Reference white sits at approximately 75% of the HLG signal range. Because of this relative design, HLG natively adapts to legacy displays without a manual trim pass in most broadcast scenarios.

Treating PQ and HLG as equivalent HDR trims is a workflow error. Step 6 (trim to SDR) applies to PQ pipelines. HLG pipelines handle SDR backwards compatibility through the OOTF.

PQ (ST 2084) HLG (BT.2100)
Transfer architecture Absolute: code value = nits Relative: adapts to display peak
Diffuse white anchor ~203 nits (~58% signal) ~75% HLG signal
Peak luminance ceiling Fixed at 10,000 nits Display-dependent (OOTF system gamma)
Legacy display compatibility None: requires ST 2086 metadata High: native SDR compatibility via OOTF
SDR trim requirement Manual pass required Usually not required for broadcast

6. Remote Session Reality Check

  • Assume client sees Rec.709 gamma 2.4
  • Assume unknown brightness
  • Assume non-calibrated display
  • Assume ambient light contamination

Judge contrast decisions on the reference display (Sony BVM-HX310).
Use the remote stream for creative direction only.
Never let browser blacks dictate reference decisions.

7. Creative Safety Checks

  • Toggle bypass on look node
  • Check waveform symmetry
  • Check YRGB parade neutrality in key neutrals
  • Check 10-step greyscale response
  • Confirm no channel-weighted toe bias (unless intentional)

8. The SMAK Rule

Technology is the tool.
Exposure is the foundation.
Reference display evaluation is the truth.

If the reference display lies, creativity lies.

Related Concepts

Principles
SMT101: Exposure Is Structural
SMT102: LUTs Are Constraint Systems
SMT106: The Pipeline Didn’t Change. The Material Did.