# What is a deep sample in OpenEXR, and how do I tell a point sample from a volume sample and which channels a deep file must have?

- id: art_01M5ME82N4WET4MNXFVMXH1KAT
- 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: 2026-10-23T13:12:17.821Z
- url: https://veyrul.com/articles/art_01M5ME82N4WET4MNXFVMXH1KAT

An OpenEXR deep pixel holds any number of samples (all channels share the count), each with a depth; Z is required and ZBack optional (copied from Z if absent); Z >= ZBack is a point sample (zero-thickness surface hit) and Z < ZBack a volume sample over [Z, ZBack); each colour or auxiliary channel needs an associated alpha found through its layer and enclosing layers. The library stores the data; the Interpreting Deep Pixels document defines the meaning.

An OpenEXR deep pixel holds any number of samples (all channels share the count), each with a depth; Z is required and ZBack optional (copied from Z if absent); Z >= ZBack is a point sample (zero-thickness surface hit) and Z < ZBack a volume sample over [Z, ZBack); each colour or auxiliary channel needs an associated alpha found through its layer and enclosing layers. The library stores the data; the Interpreting Deep Pixels document defines the meaning.

Curator qualifications: Docs and code read 2026-10-22; nothing composited (code reading, not execution).

Limitations: Docs and code read 2026-10-22; nothing composited (code reading, not execution).

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/website/InterpretingDeepPixels.rst",
      "note": "OpenEXR website/InterpretingDeepPixels.rst at 69b2604f (raw), L24, L139-216"
    },
    {
      "url": "https://github.com/AcademySoftwareFoundation/openexr/blob/69b2604fc76e370615438bdc8d2cd95b9349c12e/website/TechnicalIntroduction.rst",
      "note": "OpenEXR website/InterpretingDeepPixels.rst at 69b2604f (raw), L24, L139-216"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] An OpenEXR deep pixel holds any number of samples (all channels share the count), each with a depth; Z is required and ZBack optional (copied from Z if absent); Z >= ZBack is a point sample (zero-thickness surface hit) and Z < ZBack a volume sample over [Z, ZBack); each colour or auxiliary channel needs an associated alpha found through its layer and enclosing layers. The library stores the data; the Interpreting Deep Pixels document defines the meaning. · locator: OpenEXR website/InterpretingDeepPixels.rst at 69b2604f (raw), L24, L139-216 · source: https://github.com/AcademySoftwareFoundation/openexr/blob/69b2604fc76e370615438bdc8d2cd95b9349c12e/website/InterpretingDeepPixels.rst

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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