# What is the normative definition of MaxCLL and MaxFALL that is openly readable, and what does it say about how they are measured?

- id: art_01M5MSSFWZ1NJNCWGSCBAF93CC
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T10, T12, T19 · tags: none
- updated: 2026-10-23T16:34:02.736Z
- url: https://veyrul.com/articles/art_01M5MSSFWZ1NJNCWGSCBAF93CC

The CTA-861.3 text is paywalled, but ITU-T H.265 (V11, 01/2026) clause D.3.35 is a free primary text that defines the content light level SEI in terms CTA-861.3 relies on. Per pixel, take EMax = max(R,G,B) in linear light, convert to a light level as the CIE 1931 luminance of equal-amplitude RGB at EMax, scaled so peak white is 10,000 cd/m2 for PQ. max_content_light_level is an upper bound over all samples of the coded video sequence; max_pic_average_light_level is an upper bound on the maximum, over pictures, of the average over samples. The SEI does not itself specify the conversion from decoded samples to linear light.

The CTA-861.3 text is paywalled, but ITU-T H.265 (V11, 01/2026) clause D.3.35 is a free primary text that defines the content light level SEI in terms CTA-861.3 relies on. Per pixel, take EMax = max(R,G,B) in linear light, convert to a light level as the CIE 1931 luminance of equal-amplitude RGB at EMax, scaled so peak white is 10,000 cd/m2 for PQ. max_content_light_level is an upper bound over all samples of the coded video sequence; max_pic_average_light_level is an upper bound on the maximum, over pictures, of the average over samples. The SEI does not itself specify the conversion from decoded samples to linear light.

Curator qualifications: 'the maximum component intensity is defined as EMax = Max( ER, Max( EG, EB ) )'; light level = CIE 1931 luminance of equal-amplitude EMax 'with appropriate scaling ... peak white with 10 000 candelas per square metre when transfer_characteristics is equal to 16'; 'this SEI message does not, by itself, identify a conversion process'; max_content_light_level 'an upper bound on the maximum light level among all individual samples'; max_pic_average_light_level 'an upper bound on the maximum average light level among the samples ... for any individual picture of the CLVS'.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.265-202601-I!!PDF-E&type=items",
      "note": "ITU-T H.265 (01/2026) clause D.3.35 (curator pdftotext line 45488; printed page 389 per TOC)"
    },
    {
      "url": "https://aomediacodec.github.io/av1-spec/",
      "note": "ITU-T H.265 (01/2026) clause D.3.35 (curator pdftotext line 45488; printed page 389 per TOC)"
    },
    {
      "url": "https://docs.kernel.org/7.1/_sources/userspace-api/media/v4l/ext-ctrls-colorimetry.rst.txt",
      "note": "ITU-T H.265 (01/2026) clause D.3.35 (curator pdftotext line 45488; printed page 389 per TOC)"
    },
    {
      "url": "https://journal.smpte.org/periodicals/SMPTE%20Motion%20Imaging%20Journal/130/7/15/",
      "note": "ITU-T H.265 (01/2026) clause D.3.35 (curator pdftotext line 45488; printed page 389 per TOC)"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] The CTA-861.3 text is paywalled, but ITU-T H.265 (V11, 01/2026) clause D.3.35 is a free primary text that defines the content light level SEI in terms CTA-861.3 relies on. Per pixel, take EMax = max(R,G,B) in linear light, convert to a light level as the CIE 1931 luminance of equal-amplitude RGB at EMax, scaled so peak white is 10,000 cd/m2 for PQ. max_content_light_level is an upper bound over all samples of the coded video sequence; max_pic_average_light_level is an upper bound on the maximum, over pictures, of the average over samples. The SEI does not itself specify the conversion from decoded samples to linear light. · locator: ITU-T H.265 (01/2026) clause D.3.35 (curator pdftotext line 45488; printed page 389 per TOC) · source: https://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-H.265-202601-I!!PDF-E&type=items

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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