# How do the despill formulas in Blender (Color Spill and Keying) and Natron/openfx-misc (Despill) compare, and what do openfx-misc's ChromaKeyer documents cite?

- id: art_01M5MS0N06P29TZA13532Z6E6W
- 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: 2026-10-23T16:20:28.800Z
- url: https://veyrul.com/articles/art_01M5MS0N06P29TZA13532Z6E6W

Blender's Color Spill subtracts from the spill channel the positive excess factor*spill - limit_strength*(average of the limit channels), and Natron's Despill (credited to Wright's Digital Compositing for Film and Video, section 4.5) builds a comparable spill map with mix and expand controls and can also add red and blue into the spill area; equivalence under matched parameters is producer synthesis.

Blender's Color Spill subtracts from the spill channel the positive excess factor*spill - limit_strength*(average of the limit channels), and Natron's Despill (credited to Wright's Digital Compositing for Film and Video, section 4.5) builds a comparable spill map with mix and expand controls and can also add red and blue into the spill area; equivalence under matched parameters is producer synthesis.

Curator qualifications: Code read 2026-10-22; nothing keyed. Natron spillmap formula line and Blender Keying despill not re-read.

Limitations: Code read 2026-10-22; nothing keyed.

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/blender/blender/blob/f46990f5f55e36cc771b0ce476512b89ecfcea23/source/blender/compositor/shaders/compositor_keying_compute_image.glsl",
      "note": "library/gpu_shader_compositor_color_spill.glsl L35-56; openfx-misc Despill/Despill.cpp L45-97"
    },
    {
      "url": "https://github.com/blender/blender/blob/f46990f5f55e36cc771b0ce476512b89ecfcea23/source/blender/compositor/shaders/library/gpu_shader_compositor_color_spill.glsl",
      "note": "library/gpu_shader_compositor_color_spill.glsl L35-56; openfx-misc Despill/Despill.cpp L45-97"
    },
    {
      "url": "https://docs.blender.org/manual/en/latest/compositing/types/keying/color_spill.html",
      "note": "library/gpu_shader_compositor_color_spill.glsl L35-56; openfx-misc Despill/Despill.cpp L45-97"
    },
    {
      "url": "https://github.com/NatronGitHub/openfx-misc/blob/850b3fff65463c073bd64683e5d97a7dec2586c5/Despill/Despill.cpp",
      "note": "library/gpu_shader_compositor_color_spill.glsl L35-56; openfx-misc Despill/Despill.cpp L45-97"
    },
    {
      "url": "https://github.com/NatronGitHub/openfx-misc/blob/850b3fff65463c073bd64683e5d97a7dec2586c5/ChromaKeyer/ChromaKeyer.cpp",
      "note": "library/gpu_shader_compositor_color_spill.glsl L35-56; openfx-misc Despill/Despill.cpp L45-97"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Blender's Color Spill subtracts from the spill channel the positive excess factor*spill - limit_strength*(average of the limit channels), and Natron's Despill (credited to Wright's Digital Compositing for Film and Video, section 4.5) builds a comparable spill map with mix and expand controls and can also add red and blue into the spill area; equivalence under matched parameters is producer synthesis. · locator: library/gpu_shader_compositor_color_spill.glsl L35-56; openfx-misc Despill/Despill.cpp L45-97 · source: https://github.com/blender/blender/blob/f46990f5f55e36cc771b0ce476512b89ecfcea23/source/blender/compositor/shaders/compositor_keying_compute_image.glsl

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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