HDR Fundamentals & Core Principles 3 — Questions and Answers
Question 1: What is the key difference between HDR10 and Dolby Vision in terms of metadata?
- HDR10 uses dynamic frame-by-frame metadata; Dolby Vision uses static metadata
- HDR10 uses static metadata; Dolby Vision uses dynamic scene-by-scene or frame-by-frame metadata (Correct answer)
- HDR10 has no metadata; Dolby Vision stores metadata in the audio track
- Both use identical metadata formats but differ in color primaries
Correct answer: HDR10 uses static metadata; Dolby Vision uses dynamic scene-by-scene or frame-by-frame metadata
HDR10 relies on static MaxCLL/MaxFALL metadata applied to the entire stream, while Dolby Vision supports dynamic metadata that adjusts tone mapping on a per-scene or per-frame basis.
Question 2: The Perceptual Quantizer (PQ) transfer function was developed to align with which property of human vision?
- Peak flicker sensitivity
- The absolute threshold of luminance discrimination (Barten's CSF model) (Correct answer)
- Chromatic adaptation under daylight
- Temporal resolution at high brightness
Correct answer: The absolute threshold of luminance discrimination (Barten's CSF model)
PQ (SMPTE ST 2084) is based on Barten's Contrast Sensitivity Function, encoding values at the threshold of human luminance discrimination to maximize perceptual efficiency.
Question 3: In HDR grading, what is a 'trim pass'?
- Removing silence from the audio mix
- A secondary grade that adapts a master HDR deliverable for a different display target (Correct answer)
- Applying LUTs to log footage to normalize exposure
- The initial color correction step before creative grading
Correct answer: A secondary grade that adapts a master HDR deliverable for a different display target
A trim pass is a targeted adjustment made to an HDR master to optimize its appearance for a specific display tier (e.g., adapting a 4000-nit master for a 1000-nit consumer TV).
Question 4: Which standard defines the PQ (Perceptual Quantizer) transfer function used in HDR10 and Dolby Vision?
- ITU-R BT.2020
- SMPTE ST 2084 (Correct answer)
- ITU-R BT.709
- ISO 22028-2
Correct answer: SMPTE ST 2084
SMPTE ST 2084 is the standard that formally specifies the PQ EOTF, supporting peak luminance up to 10,000 nits.
Question 5: What is MaxCLL in HDR10 metadata?
- Maximum Color Luminance Level — the brightest color channel value in the stream
- Maximum Content Light Level — the highest luminance of any single pixel across the entire content (Correct answer)
- Maximum Chroma Luma Level — the saturation ceiling for highlights
- Maximum Contrast Light Level — the peak-to-black ratio
Correct answer: Maximum Content Light Level — the highest luminance of any single pixel across the entire content
MaxCLL (Maximum Content Light Level) specifies the highest luminance value of any single pixel across all frames of the entire HDR content, expressed in nits.
Question 6: Why is the HLG (Hybrid Log-Gamma) transfer function described as 'backward compatible' with SDR displays?
- HLG uses the same BT.709 color primaries as SDR
- The lower portion of the HLG curve approximates a standard gamma curve, rendering acceptably on SDR displays without a separate SDR version (Correct answer)
- HLG automatically converts to SDR via metadata embedded in the signal
- HLG clips all values above 100 nits to match SDR range
Correct answer: The lower portion of the HLG curve approximates a standard gamma curve, rendering acceptably on SDR displays without a separate SDR version
HLG's lower signal range closely follows a traditional gamma response, so an SDR display can interpret the signal and produce a usable — if not optimized — image without special processing.
Question 7: What is the reference white level defined by SMPTE ST 2084 (PQ) for HDR mastering monitors?
- 100 nits
- 203 nits (Correct answer)
- 400 nits
- 1,000 nits
Correct answer: 203 nits
SMPTE ST 2084 and associated guidelines (ST 2094) define 203 nits as the reference diffuse white for HDR content, providing headroom above this level for specular highlights.
HDR Fundamentals & Core Principles 3
What is the key difference between HDR10 and Dolby Vision in terms of metadata?