# Where does OpenEXR v3.5.2's default scanline deep compositor differ from the tidy/flatten procedure in the documents?

- id: art_01M5MEJGQRWJVTDB2R8GZEGMW5
- 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 · tags: none
- updated: 2026-10-23T13:17:59.923Z
- url: https://veyrul.com/articles/art_01M5MEJGQRWJVTDB2R8GZEGMW5

OpenEXR's default deep compositor sorts samples by Z, then ZBack, then input index (only when compositing more than one source) and accumulates them front to back with an early exit at full alpha; it has no split or merge step, so for overlapping volumes it does not implement the documented tidy-then-flatten procedure, and a single-source pixel is assumed already sorted.

OpenEXR's default deep compositor sorts samples by Z, then ZBack, then input index (only when compositing more than one source) and accumulates them front to back with an early exit at full alpha; it has no split or merge step, so for overlapping volumes it does not implement the documented tidy-then-flatten procedure, and a single-source pixel is assumed already sorted.

Curator qualifications: Code read 2026-10-22; no images composited. InterpretingDeepPixels.rst tidy/flatten definitions from producer reading (CA-B235 covered the docs).

Limitations: Code read 2026-10-22; no images composited.

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/openexr/blob/69b2604fc76e370615438bdc8d2cd95b9349c12e/src/lib/OpenEXR/ImfCompositeDeepScanLine.h",
      "note": "ImfDeepCompositing.cpp at 69b2604f L37-73"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/openexr/blob/69b2604fc76e370615438bdc8d2cd95b9349c12e/website/InterpretingDeepPixels.rst",
      "note": "ImfDeepCompositing.cpp at 69b2604f L37-73"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/openexr/blob/69b2604fc76e370615438bdc8d2cd95b9349c12e/src/lib/OpenEXR/ImfDeepCompositing.cpp",
      "note": "ImfDeepCompositing.cpp at 69b2604f L37-73"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/openexr/blob/69b2604fc76e370615438bdc8d2cd95b9349c12e/src/lib/OpenEXR/ImfCompositeDeepScanLine.cpp",
      "note": "ImfDeepCompositing.cpp at 69b2604f L37-73"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] OpenEXR's default deep compositor sorts samples by Z, then ZBack, then input index (only when compositing more than one source) and accumulates them front to back with an early exit at full alpha; it has no split or merge step, so for overlapping volumes it does not implement the documented tidy-then-flatten procedure, and a single-source pixel is assumed already sorted. · locator: ImfDeepCompositing.cpp at 69b2604f L37-73 · source: https://github.com/AcademySoftwareFoundation/openexr/blob/69b2604fc76e370615438bdc8d2cd95b9349c12e/src/lib/OpenEXR/ImfCompositeDeepScanLine.h

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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