# What are the WCAG 2.2 contrast-ratio and relative-luminance formulas and thresholds (1.4.3, 1.4.11), and what in them applies to text burned into video?

- id: art_01M5MV0VK6FP2G5JHZ4J3GT73B
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T12, T17, T20 · tags: none
- updated: 2026-10-23T16:55:32.704Z
- url: https://veyrul.com/articles/art_01M5MV0VK6FP2G5JHZ4J3GT73B

WCAG 2.2 (Recommendation, 12 Dec 2024) defines contrast ratio as (L1 + 0.05) / (L2 + 0.05) with sRGB relative luminance L = 0.2126 R + 0.7152 G + 0.0722 B (linearised with the 0.04045 piecewise function). 1.4.3 requires 4.5:1 for text and 3:1 for large-scale text (18 pt or 14 pt bold); 1.4.11 requires 3:1 for UI components and graphical objects. These are web-content criteria: the criteria and Understanding pages read say nothing about video frames or captions, exempt text that is 'part of a picture that contains significant other visual content', and tell authors to evaluate in sRGB unless another colour space is known. For video, the specs read (BBC, DPP/Channel 4, Netflix) give no contrast ratios, so a WCAG ratio applied to burned-in text is a borrowed rule, not a video rule.

WCAG 2.2 (Recommendation, 12 Dec 2024) defines contrast ratio as (L1 + 0.05) / (L2 + 0.05) with sRGB relative luminance L = 0.2126 R + 0.7152 G + 0.0722 B (linearised with the 0.04045 piecewise function). 1.4.3 requires 4.5:1 for text and 3:1 for large-scale text (18 pt or 14 pt bold); 1.4.11 requires 3:1 for UI components and graphical objects. These are web-content criteria: the criteria and Understanding pages read say nothing about video frames or captions, exempt text that is 'part of a picture that contains significant other visual content', and tell authors to evaluate in sRGB unless another colour space is known. For video, the specs read (BBC, DPP/Channel 4, Netflix) give no contrast ratios, so a WCAG ratio applied to burned-in text is a borrowed rule, not a video rule.

Curator qualifications: Excerpted evidence located; WCAG 2.2 contrast/relative luminance formulas and thresholds (links T17.03).

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

```json
{
  "citations": [
    {
      "url": "https://www.w3.org/TR/WCAG22/",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://www.w3.org/WAI/WCAG22/Understanding/contrast-minimum.html",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://www.w3.org/WAI/WCAG22/Understanding/non-text-contrast.html",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://web.archive.org/web/20260713055110id_/https://partnerhelp.netflixstudios.com/hc/en-us/articles/360034536253-Titles-Graphics-Requirements-Best-Practices",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://www.bbc.co.uk/accessibility/forproducts/guides/subtitles",
      "note": "candidate evidence excerpts"
    },
    {
      "url": "https://eastoverhill.co.uk/techref/technical_delivery_standards.pdf",
      "note": "candidate evidence excerpts"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] WCAG 2.2 (Recommendation, 12 Dec 2024) defines contrast ratio as (L1 + 0.05) / (L2 + 0.05) with sRGB relative luminance L = 0.2126 R + 0.7152 G + 0.0722 B (linearised with the 0.04045 piecewise function). 1.4.3 requires 4.5:1 for text and 3:1 for large-scale text (18 pt or 14 pt bold); 1.4.11 requires 3:1 for UI components and graphical objects. These are web-content criteria: the criteria and Understanding pages read say nothing about video frames or captions, exempt text that is 'part of a picture that contains significant other visual content', and tell authors to evaluate in sRGB unless another colour space is known. For video, the specs read (BBC, DPP/Channel 4, Netflix) give no contrast ratios, so a WCAG ratio applied to burned-in text is a borrowed rule, not a video rule. · locator: candidate evidence excerpts · source: https://www.w3.org/TR/WCAG22/

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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