# What colour information survives export to PNG/web, which chunk wins when several are present, and what is assumed when an image is untagged?

- id: art_01M5MDGD237E2SDPDZMAKEGR37
- 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 · tags: none
- updated: 2026-10-23T12:59:22.045Z
- url: https://veyrul.com/articles/art_01M5MDGD237E2SDPDZMAKEGR37

PNG Third Edition (W3C Recommendation, 24 June 2025) ranks colour chunks cICP 1, iCCP 2, sRGB 3, cHRM+gAMA 4 and says the lowest number 'should' take precedence with the others ignored (decoders use the highest-precedence chunk they understand); mDCV is informative mastering-display metadata that must be accompanied by cICP; CSS Color 4 says untagged images must be treated as sRGB.

PNG Third Edition (W3C Recommendation, 24 June 2025) ranks colour chunks cICP 1, iCCP 2, sRGB 3, cHRM+gAMA 4 and says the lowest number 'should' take precedence with the others ignored (decoders use the highest-precedence chunk they understand); mDCV is informative mastering-display metadata that must be accompanied by cICP; CSS Color 4 says untagged images must be treated as sRGB.

Curator qualifications: Normative strength: the precedence rule uses 'should', and decoders that do not understand cICP fall back to the next chunk they understand; do not render it as an absolute 'wins'. ICC v2/v4 PCS statements (S23, E5/F2) and PNG decoder gamma section (E6) not reinspected. CSS Color 4 is a Candidate Recommendation Draft; live TR text. Specification reading only; no PNG encoded or decoded.

Limitations: Specification reading only; no PNG encoded or decoded.

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/png-3/",
      "note": "w3.org/TR/png-3 (REC 2025-06-24), section 4 colour-chunk paragraph and Table 1; section 11.3.2.7 mDCV; CSS Color 4 (TR copy fetched 2026-10-22) section on untagged images"
    },
    {
      "url": "https://www.color.org/specification/ICC.1-2022-05.pdf",
      "note": "w3.org/TR/png-3 (REC 2025-06-24), section 4 colour-chunk paragraph and Table 1; section 11.3.2.7 mDCV; CSS Color 4 (TR copy fetched 2026-10-22) section on untagged images"
    },
    {
      "url": "https://www.w3.org/TR/css-color-4/",
      "note": "w3.org/TR/png-3 (REC 2025-06-24), section 4 colour-chunk paragraph and Table 1; section 11.3.2.7 mDCV; CSS Color 4 (TR copy fetched 2026-10-22) section on untagged images"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] PNG Third Edition (W3C Recommendation, 24 June 2025) ranks colour chunks cICP 1, iCCP 2, sRGB 3, cHRM+gAMA 4 and says the lowest number 'should' take precedence with the others ignored (decoders use the highest-precedence chunk they understand); mDCV is informative mastering-display metadata that must be accompanied by cICP; CSS Color 4 says untagged images must be treated as sRGB. · locator: w3.org/TR/png-3 (REC 2025-06-24), section 4 colour-chunk paragraph and Table 1; section 11.3.2.7 mDCV; CSS Color 4 (TR copy fetched 2026-10-22) section on untagged images · source: https://www.w3.org/TR/png-3/

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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