by Denis Trutanic, lead camera td @ Weta Digital on King Kong

Weta Digital's camera department has used 3D-Equalizer (3DE) to complete more than 2200 complex matchmoving tasks on King Kong. I would like to describe some key features, which in my opinion are responsible for 3DE's accuracy, efficiency and reliability.


At the beginning of every matchmove I created a 'buffer compression file'. This means, that the entire sequence is compressed and stored in one single file, which is loaded into memory. Images are decompressed on demand, during tracking or scrubbing through the sequence. Don't worry about quality, the compression doesn't affect the tracking accuracy at all!
Due to the compression file it's possible to load about 15 times more images into RAM, so that even very long 2k-sequences can be completely kept in memory.
This feature speeds up the workflow dramatically, particularly on dual core/CPU systems, since it's multithreaded!


To increase tracking accuracy, it's important to have tracking pattern/markers on a contrasting background.
A quite interesting way to enhance image contrast in 3DE is the Sequence requester's '8 bit Color Conversion' section, where Black/White Point, Gamma and SoftClip are adjustable. This even works fine with 8-bit images, but unfolds it's power on higher bit depths.
On simple tasks I used Equalizer's 'Image Controls' feature since it's a little bit limited and odd to use, but a highly improved 'Image Controls' feature is currently under development! However, 3DE is not a compositing software!
On difficult plates I used Shake to convert them into a kind of black and white high contrast images. Equalizer offers a very elegant way to add these images as an alternative sequence to the original sequence node. 3DE accepts up to 4 sequences per sequence node, function keys F5-F8 allow to switch between them quickly.


Equalizer's tracker is very accurate, robust and easy to use - not overloaded with tons of adjustable parameters. Additional to pattern tracking 3DE offers a unique marker tracking mode as well. To control tracking I always turned on the smart 'auto center' option, so that the currently selected point is automatically centered in the Zoom Window’s display area and visible during the whole tracking process.
Although there have been survey data for all sets, I sometimes used 'Reference Frames' or a second sequence, shot from a different point of view, to create further survey information. In almost all shots I additionally tracked survey-free features as well. 3DE is very flexible, it can handle surveyed, survey-free and auto tracked points in one project.
Point weighting was also a very powerful feature on challenging shots. The 'Point Weight' parameter makes a point more or less important with respect to other points.
A TCL script (3dequalizer.com -> tech articles) enabled the export of 2D tracking data to Shake. 2D tracking curves can also be exported in ASCII format, in order to import them e.g. into Nuke (a TCL 3D camera path export to Nuke is also available). Due to 3DE's TCL scripting capability it's possible to create custom export filters for 2D curves as well as 3D camera paths for almost every software.
That's why other departments could benefit from Equalizer's very precise 2D tracks as well. I also used the auto tracker to create point clouds for terrain modeling.


Actually editing the 3D motion curves should always be the last step in a matchmoving process and should be avoided if possible! But life isn't perfect and by lack of useful tracking features, this could become necessary. Equalizer saved me a lot of time on a couple of shots with it's 'Make Rot. & Pos. Curves Consistent' feature in the 'Motion Path Window'. Each time a position curve has been edited, the rotation curves are made consistent, or vice versa. In combination with geo-data as a visual reference (3DE offers OBJ import), this feature relieves the motion curves editing vastly.


There were a lot of set extensions on Kong, particularly on New York shots. The accuracy demanded for these shots couldn't have been achieved without taking lens distortion into account. Usually it was sufficient to calculate focal length and the basic lens distortion parameter, but some lenses required the use of quartic distortion parameter as well. In theses cases I imported lens information which has been determined by alining Equalizer's distortion grid to grid shots (quartic distortion can't be calculated). Anyhow I recalculated focal length and basic distortion parameter of these library data to fine adjust the solve. The recalculation was necessary since focal length alters slightly with different focus and lens distortion depends on focal length.
To check the accuracy of my matchmoves I de-warped the sequence with Equalizer's 'Warp Distort' software before playblasting a preview in Maya. It's very handy to use Warp Distort, just open Equalizer's project file and all distortion values are set up. Warp Distort can be used as command line tool as well.


Last but not least I shouldn't forget to mention Equalizer's excellent solver, which made it possible to get the most challenging shots done.



Images: KING KONG © UNIVERSAL PICTURES. All Rights Reserved. FX by Weta Digital.