[Bf-docboard-svn] bf-manual: [7285] trunk/blender_docs/manual: Brown-Conrady lens distortion model

[Aaron Carlisle]

Revision: 7285
          https://developer.blender.org/rBM7285
Author:   Blendify
Date:     2020-10-28 19:40:10 +0100 (Wed, 28 Oct 2020)
Log Message:
-----------
Brown-Conrady lens distortion model

Author: @Ssh4

Differential Revision: https://developer.blender.org/D9296

Modified Paths:
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    trunk/blender_docs/manual/movie_clip/tracking/clip/properties/track/camera.rst

Added Paths:
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    trunk/blender_docs/manual/images/movie_clip_tracking_clip_properties_track_camera_lens_distortion_k.png
    trunk/blender_docs/manual/images/movie_clip_tracking_clip_properties_track_camera_lens_distortions_p.png

Added: trunk/blender_docs/manual/images/movie_clip_tracking_clip_properties_track_camera_lens_distortion_k.png
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--- trunk/blender_docs/manual/images/movie_clip_tracking_clip_properties_track_camera_lens_distortion_k.png	2020-10-28 06:53:04 UTC (rev 7284)
+++ trunk/blender_docs/manual/images/movie_clip_tracking_clip_properties_track_camera_lens_distortion_k.png	2020-10-28 18:40:10 UTC (rev 7285)

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--- trunk/blender_docs/manual/images/movie_clip_tracking_clip_properties_track_camera_lens_distortions_p.png	2020-10-28 06:53:04 UTC (rev 7284)
+++ trunk/blender_docs/manual/images/movie_clip_tracking_clip_properties_track_camera_lens_distortions_p.png	2020-10-28 18:40:10 UTC (rev 7285)

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Modified: trunk/blender_docs/manual/movie_clip/tracking/clip/properties/track/camera.rst
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--- trunk/blender_docs/manual/movie_clip/tracking/clip/properties/track/camera.rst	2020-10-28 06:53:04 UTC (rev 7284)
+++ trunk/blender_docs/manual/movie_clip/tracking/clip/properties/track/camera.rst	2020-10-28 18:40:10 UTC (rev 7285)
@@ -23,7 +23,9 @@
    but it can be different in some special cases. Check camera/lens specifications in such cases.
    To set the optical center to the center of image, there is a *Set Center* button below the sliders.
 
+   .. tip:: Optical Center also know as Principal Point in photogrammetry.
 
+
 Lens
 ====
 
@@ -35,20 +37,44 @@
    Mathematical function to convert distorted to undistorted coordinates.
 
    Polynomial
-      Polynomial radial distortion.
+      Polynomial radial distortion. Uses three distortion coefficients: K1, K2, and K3.
    Division
       It defines high distortions, which makes this model suitable much better for cameras with fisheye lenses.
+      Use two distortion coefficients: K1, K2.
    Nuke
-      Distortion model used by the Nuke compositor.
+      Distortion model used by the Nuke compositor. Use two distortion coefficients K1, K2.
+   Brown
+      Brown-Conrady is one of most advanced mathematical lens distortion models.
+      Used to model both radial and tangential distortion. Can use up to four
+      radial distortion coefficients: K1-K4 and up to two tangential distortion coefficients: P1 and P2.
 
 Coefficients
    Coefficients are used to compensate for lens distortion when the movie was shot.
    Currently these values can be tweaked by hand only (there are no calibration tools yet)
-   using tools available in Distortion mode.
-   Basically, just tweak K1 until solving is most accurate for the known focal length
-   (but also take grid and annotations into account to prevent "impossible" distortion).
+   using tools available in Distortion mode. Basically, just tweak K1 until solving is most
+   accurate for the known focal length (but also take grid and annotations into account
+   to prevent "impossible" distortion).
 
-   The coefficients of the division model work independent from each other and
-   positive values will give a barrel distortion.
+   Radial distortion coefficients (K1-K4)
+      The coefficients in lens distortion models work independent from each other
+      and positive values will give a barrel distortion. Negative values give pincushion distortion.
+      A mixture of both negative and positive coefficients allow define more complicated
+      mustache distortions or complex distortion, that is less common but not rare.
 
-   K1, K2 and K3
+      .. figure:: /images/movie_clip_tracking_clip_properties_track_camera_lens_distortion_k.png
+
+         Example of radial distortion for positive and negative K coefficients
+
+   Tangential distortion coefficients (P1,P2)
+      Work independent and allow compensate situations when sensor is not perpendicular to a group of lens.
+      P1 is used to compensate for sensor rotation in Z (vertical) axes,
+      while P2 is for compensating sensor rotation in X (horizontal) axes.
+      Such distortions can be found in source from cameras with sensor stabilization system.
+
+      .. figure:: /images/movie_clip_tracking_clip_properties_track_camera_lens_distortions_p.png
+
+         Example of tangential distortion for P1, P2 coefficients
+
+Optical Center (Principal Point) is important value in camera lens distortion,
+it can be shifted (distorted) from sensor center in images from cameras with sensor stabilization.
+And using correct values can increase quality of clip undistortion results.