# Where do the lens-distortion models of matchmove and compositing tools (Nuke, SynthEyes, OpenCV, Blender/libmv, COLMAP, 3DE, OpenTrackIO) disagree, and what parameters must travel with a shot for the distortion to be reproduced?

- id: art_01M5MD03M5BZFCRC1B84XSA1BA
- 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, T19 · tags: none
- updated: 2026-10-23T12:50:28.094Z
- url: https://veyrul.com/articles/art_01M5MD03M5BZFCRC1B84XSA1BA

Reading pinned vendor docs and source, the models disagree in at least five ways: direction (Blender division applies x/(1+k r^2) from ideal normalised to image; Nuke Classic and COLMAP SIMPLE_DIVISION use the same form from distorted to ideal), the meaning of k4 (OpenCV: a rational denominator term; Blender Brown: an r^8 polynomial term), the roles of p1 and p2 (Blender Brown is swapped relative to OpenCV, COLMAP and Blender Polynomial, from code reading), the normalisation (OpenCV by z with focal in pixels; Nuke width/height/diagonal/maximum; Blender Nuke model by half the larger image side; OpenTrackIO offsets in mm), and pixel origin conventions. For the shot to be reproducible the record must carry model name, direction, coefficient order and units, normalisation, centre/offset, sensor size and resolution, focal length and the focus/zoom state; an STMap or projection screen is the model-free alternative with storage and precision costs. 3DEqualizer model equations were not read...

Reading pinned vendor docs and source, the models disagree in at least five ways: direction (Blender division applies x/(1+k r^2) from ideal normalised to image; Nuke Classic and COLMAP SIMPLE_DIVISION use the same form from distorted to ideal), the meaning of k4 (OpenCV: a rational denominator term; Blender Brown: an r^8 polynomial term), the roles of p1 and p2 (Blender Brown is swapped relative to OpenCV, COLMAP and Blender Polynomial, from code reading), the normalisation (OpenCV by z with focal in pixels; Nuke width/height/diagonal/maximum; Blender Nuke model by half the larger image side; OpenTrackIO offsets in mm), and pixel origin conventions. For the shot to be reproducible the record must carry model name, direction, coefficient order and units, normalisation, centre/offset, sensor size and resolution, focal length and the focus/zoom state; an STMap or projection screen is the model-free alternative with storage and precision costs. 3DEqualizer model equations were not read (they sit in a 246 MB archive).

Curator qualifications: Nuke 17.1v2: 'Direction distortionModelDirection Forward ... Forward - estimated directly but needs to be inverted for image rendering. The NukeX Classic model is an example of a Forward model. Backward - estimated using its inverse but can be used directly for image rendering. Model inversion is not an exact process'. camdkit: default model 'Brown-Conrady D-U'; docstring lines 188-189: '"Brown-Conrady D-U" when mapping distorted to undistorted coordinates, and "Brown-Conrady U-D" when mapping undistorted to undistorted coordinates'. Code models per C3R-0049 (OpenCV k4 rational; libmv Brown k4 r^8 and p1/p2 swapped). Rights/verification notes are shown as limitations (L00 0019/ADR-0011): they restrict reuse of the cited material or record what was not verified; they are not cleared by this summary.

Limitations: [rights_conflict_record] Blender licence NOASSERTION vs libmv MIT header (rights conflict) as in C3R-0049.

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/opencv/opencv/blob/fe38fc608f6acb8b68953438a62305d8318f4fcd/modules/calib3d/include/opencv2/calib3d.hpp",
      "note": "see curator disposition"
    },
    {
      "url": "https://github.com/blender/blender/blob/95476576989343cfe4ef3bfb81dee322ff7294a7/intern/libmv/libmv/simple_pipeline/distortion_models.h",
      "note": "see curator disposition"
    },
    {
      "url": "https://learn.foundry.com/nuke/content/reference_guide/transform_nodes/lensdistortion.html",
      "note": "see curator disposition"
    },
    {
      "url": "https://github.com/colmap/colmap/blob/526ff008d2762292daa6e9dc027d7f2bc1a4aa17/src/colmap/sensor/models/division.h",
      "note": "see curator disposition"
    },
    {
      "url": "https://github.com/colmap/colmap/blob/526ff008d2762292daa6e9dc027d7f2bc1a4aa17/src/colmap/sensor/models/opencv.h",
      "note": "see curator disposition"
    },
    {
      "url": "https://borisfx.com/documentation/syntheyes/syntheyesum_files/lens_distortion_models/",
      "note": "see curator disposition"
    },
    {
      "url": "https://github.com/SMPTE/ris-osvp-metadata-camdkit/blob/0362321d03721a07029329cfc6f9e1e47bfa2bdf/src/main/python/camdkit/lens_types.py",
      "note": "see curator disposition"
    },
    {
      "url": "https://borisfx.com/documentation/syntheyes/syntheyesum_files/lens_distortion_interchange_1/",
      "note": "see curator disposition"
    },
    {
      "url": "https://borisfx.com/documentation/syntheyes/syntheyesum_files/lens_distortion_interchange_2/",
      "note": "see curator disposition"
    },
    {
      "url": "https://borisfx.com/documentation/syntheyes/syntheyesum_files/lens_distortion_profiles/",
      "note": "see curator disposition"
    },
    {
      "url": "https://www.3dequalizer.com/?site=tech_docs&id=110216_01",
      "note": "see curator disposition"
    },
    {
      "url": "https://github.com/colmap/colmap/blob/526ff008d2762292daa6e9dc027d7f2bc1a4aa17/src/colmap/sensor/models.h",
      "note": "see curator disposition"
    },
    {
      "url": "https://github.com/blender/blender/blob/95476576989343cfe4ef3bfb81dee322ff7294a7/intern/libmv/libmv/simple_pipeline/distortion_models.cc",
      "note": "see curator disposition"
    },
    {
      "url": "https://borisfx.com/documentation/syntheyes/syntheyesum_files/lens_workflow/",
      "note": "see curator disposition"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Reading pinned vendor docs and source, the models disagree in at least five ways: direction (Blender division applies x/(1+k r^2) from ideal normalised to image; Nuke Classic and COLMAP SIMPLE_DIVISION use the same form from distorted to ideal), the meaning of k4 (OpenCV: a rational denominator term; Blender Brown: an r^8 polynomial term), the roles of p1 and p2 (Blender Brown is swapped relative to OpenCV, COLMAP and Blender Polynomial, from code reading), the normalisation (OpenCV by z with focal in pixels; Nuke width/height/diagonal/maximum; Blender Nuke model by half the larger image side; OpenTrackIO offsets in mm), and pixel origin conventions. For the shot to be reproducible the record must carry model name, direction, coefficient order and units, normalisation, centre/offset, sensor size and resolution, focal length and the focus/zoom state; an STMap or projection screen is the model-free alternative with storage and precision costs. 3DEqualizer model equations were not read (they sit in a 246 MB archive). · locator: see curator disposition · source: https://github.com/opencv/opencv/blob/fe38fc608f6acb8b68953438a62305d8318f4fcd/modules/calib3d/include/opencv2/calib3d.hpp

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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