Calibration is a critical part of capturing data with stereo camera pair to enable a high-quality data reconstruction. This section shows an example of how to calibrate correctly.
Calibration Board Construction
Calibration requires a calibration board (checkerboard pattern). The default settings for the calibration process are for a checkerboard pattern with a size of 89.5 mm x 134.2 mm and each square measuring 7.5 mm.
You can use the sample from the MetaHuman Calibration Processing plugin found in the following directory:
/Engine/Plugins/MetaHuman/MetaHumanCalibrationProcessing/Content/Boards
The following is a list of recommendations to ensure best results:
If possible, the pattern should be directly printed onto a white rigid surface like an aluminum composite panel. If that is not possible, a high-quality paper that is carefully attached to a rigid surface with spray adhesive may suffice.
The board should be completely flat with no warping or wrinkling of any kind.
The board should be matte to avoid strong reflections.
The corners of the grid squares on the board should be clear and sharp.
You should ensure the board has no marks or chips, especially on the grid corners.
The calibration board should have a handle on the back so the operator can hold it without occluding the pattern.
If using a board of different pattern dimensions, ensure the board has opposing colors in its diagonal corners, allowing 180 degree rotations to be detected.
Operation
Specific calibration footage should be taken at the start and the end of a capture session to bookend the shoot. Calibration footage may be captured at other times during the shoot if the helmet needs to be significantly adjusted or the cameras are otherwise compromised.
When capturing a calibration take, the board should start in a ‘neutral’, forward-facing position towards the camera. During calibration capture, you are attempting to paint the space with the calibration board. For each capture, the board should be moved across the field of view, including movements of up, down, left, right, roll, and pitch, in the plane where the performer’s face will be or was positioned. The video should be approximately 20 seconds long. See the example below.
Correct calibration
The following images show examples of poor calibration techniques.
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Too close | Too far | Out of frame | Occluded by hand | Hand visible |
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Board inverted | Board horizontal | Over-rotated | Calibration with actor |
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