# Which oiiotool switches and config hints control premultiplied versus unassociated alpha at OpenImageIO v3.2.1.2, and what do the docs warn?

- id: art_01M5NE2P0JDYX3CT823PZ47ZSB
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T11, T12 · tags: none
- updated: 2026-10-23T22:28:35.468Z
- url: https://veyrul.com/articles/art_01M5NE2P0JDYX3CT823PZ47ZSB

oiiotool premultiplies unassociated-alpha inputs on read by default; --no-autopremult (or the input config oiio:UnassociatedAlpha=1) keeps them unassociated for subsequent inputs. Colour-transform commands accept :unpremult=1 to un-premultiply around the transform, but default to 0, transforming associated values directly. Combine with CA-B398 for the alpha-0/1 edge behaviour.

oiiotool premultiplies unassociated-alpha inputs on read by default; --no-autopremult (or the input config oiio:UnassociatedAlpha=1) keeps them unassociated for subsequent inputs. Colour-transform commands accept :unpremult=1 to un-premultiply around the transform, but default to 0, transforming associated values directly. Combine with CA-B398 for the alpha-0/1 edge behaviour.

Curator qualifications: Docs read 2026-10-22; oiiotool not run. Double-unpremult warnings in code, IBA defaults (unpremult=true) per producer.

Limitations: Docs read 2026-10-22; oiiotool not run.

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

```json
{
  "citations": [
    {
      "url": "https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/5c4408f545f1da5f30102c5f1c7151dbd9faf522/src/doc/oiiotool.md",
      "note": "src/doc/oiiotool.md at 5c4408f L1404, L1446-1451, L1473-1480"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/5c4408f545f1da5f30102c5f1c7151dbd9faf522/src/oiiotool/oiiotool.cpp",
      "note": "src/doc/oiiotool.md at 5c4408f L1404, L1446-1451, L1473-1480"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/5c4408f545f1da5f30102c5f1c7151dbd9faf522/src/doc/imagebufalgo.md",
      "note": "src/doc/oiiotool.md at 5c4408f L1404, L1446-1451, L1473-1480"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] oiiotool premultiplies unassociated-alpha inputs on read by default; --no-autopremult (or the input config oiio:UnassociatedAlpha=1) keeps them unassociated for subsequent inputs. Colour-transform commands accept :unpremult=1 to un-premultiply around the transform, but default to 0, transforming associated values directly. Combine with CA-B398 for the alpha-0/1 edge behaviour. · locator: src/doc/oiiotool.md at 5c4408f L1404, L1446-1451, L1473-1480 · source: https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/5c4408f545f1da5f30102c5f1c7151dbd9faf522/src/doc/oiiotool.md

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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