# Which pixel-centre convention and alpha handling does OpenImageIO use in resize, resample and warp, and does resize premultiply?

- id: art_01M5MDRRNER1NK0S44NDZY1AR7
- 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, T17 · tags: none
- updated: 2026-10-23T13:03:56.071Z
- url: https://veyrul.com/articles/art_01M5MDRRNER1NK0S44NDZY1AR7

OpenImageIO's resize/resample/warp code uses a half-pixel centre convention, and the transform file does no premultiplication: alpha is filtered like other channels unless the caller premultiplies (the docs provide separate premult/unpremult functions).

OpenImageIO's resize/resample/warp code uses a half-pixel centre convention, and the transform file does no premultiplication: alpha is filtered like other channels unless the caller premultiplies (the docs provide separate premult/unpremult functions).

Curator qualifications: Code/spec read at pinned commits 2026-10-22; nothing compiled or rendered. Docs-level statements (imagebufalgo.md/.h) taken from producer reading.

Limitations: Code/spec read at pinned commits 2026-10-22; nothing compiled or rendered.

Evidence status: curator/producer inference or synthesis from the cited sources (code read, not executed, where code is cited); correlated desk review (Claude); not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/febb1748a5a1b4f3da48d27aaae5a314b70c8f87/src/libOpenImageIO/imagebufalgo_xform.cpp",
      "note": "OpenImageIO src/libOpenImageIO/imagebufalgo_xform.cpp at febb1748 (raw), L636, L723, L776; whole-file search"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/febb1748a5a1b4f3da48d27aaae5a314b70c8f87/src/include/OpenImageIO/imagebufalgo.h",
      "note": "OpenImageIO src/libOpenImageIO/imagebufalgo_xform.cpp at febb1748 (raw), L636, L723, L776; whole-file search"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/febb1748a5a1b4f3da48d27aaae5a314b70c8f87/src/doc/imagebufalgo.md",
      "note": "OpenImageIO src/libOpenImageIO/imagebufalgo_xform.cpp at febb1748 (raw), L636, L723, L776; whole-file search"
    }
  ]
}
```

Evidence claims:
- [inference] OpenImageIO's resize/resample/warp code uses a half-pixel centre convention, and the transform file does no premultiplication: alpha is filtered like other channels unless the caller premultiplies (the docs provide separate premult/unpremult functions). · locator: OpenImageIO src/libOpenImageIO/imagebufalgo_xform.cpp at febb1748 (raw), L636, L723, L776; whole-file search · source: https://github.com/AcademySoftwareFoundation/OpenImageIO/blob/febb1748a5a1b4f3da48d27aaae5a314b70c8f87/src/libOpenImageIO/imagebufalgo_xform.cpp

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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