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Calibration

Stereo 3D calibration is the process of calculating the position and orientation of two cameras relative to each other.

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It is recommended that before any work using stereo 3D is done, this calibration process be completed first.

Setting Up Cameras for Calibration

Calibration uses the same setup as stereo 3D capture. Refer to the Decapod Stereo 3D Guide.

Connect Right Camera First (Applies to Tethered Capture Only)

Before doing any calibration of capturing, the right camera must be attached to the Decapod system first, then the left camera. Doing this out of order may cause stereo capture and subsequent dewarping to not perform properly.

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Note:
If any camera is disconnected during capture, both cameras should be disconnected and reconnected in the manner stated above (left camera first, then right camera). If this is done in reverse order, stereo 3D dewarp may not perform properly.

Taking Calibration Photos

To perform calibration, a 10x7 checkerboard pattern is held in full view of both cameras and pictures are taken. Between taking each pair of photos, the checkerboard is tilted differently or its position changed before another photo is taken.

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Warning

When the cameras are in place, do not change their positions or orientation relative to each other during the calibration process or during stereo capture. If camera positioning is changed, the images captured up to this point should be deleted and the calibration process restarted.

Calibration capture procedure:

  1. Position checkerboard in front of cameras, and ensure checkerboard is visible from both cameras. If checkerboard is not completely visible, then adjust the cameras higher, or place the subject lower.
  2. Take test captures to ensure proper positioning. These test captures should be deleted and not be included in the final set calibration images.
  3. While holding the checkerboard still, take a picture with both cameras. The Decapod capture tool can be helpful in this situation as it can take pictures from both cameras simultaneously.
  4. Change the tilt / position / orientation of the checkerboard while ensuring it is viewable by both cameras.
  5. Repeat Steps 3 to 4 until at least 23 pairs of photos are taken.
  6. If cameras are bumped or change positions, delete all calibration photos taken so far and start again from step 1.

Example Calibration Capture Process

Calibration Image Filename Convention (Applies to Untethered Capture Only)

Stereo 3D Calibration expects at least 23 image pairs that follow this filename format:

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  • taking photos simultaneously from both cameras which can be faster than triggering the cameras manually.
  • the Decapod Capture tool also creates a ZIP file of the images (with proper file names) so it can be used directly in the Stereo 3D Calibration tool without additional work.

Important: Do not Change Relative Camera Positions

Once the calibration photos are taken, do not change the relative positions of cameras. Treat the pair of cameras as a single unit and do not turn or twist any cameras once mounted. Do not bump them accidentally.

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Mixing and matching different stereo image sets and different calibration data is strongly discouraged.

How Run Stereo 3D Calibration

Once all checkerboard calibration images are taken, calibration data needs to be generated by running the Decapod Stereo 3D Calibration tool.

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<code>calibration.zip</code> file is needed later for stereo dewarping, so it is recommended that the file be saved in a safe location, preferably the same directory where work is being done. This way it is clear that certain calibration data belongs with a particular unit of work.

Capture stuff below

By default the address for Decapod Capture is: http://localhost:8081.

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Note
titleNote:

Remove any memory cards from the cameras prior to attaching to the Decapod system. If a memory card is present in the camera and the camera is connected to Decapod, the operating system may mount the memory card and prevent Decapod from using the cameras. You will have to disconnect the USB cable, remove the memory card, and then reconnect the cable.

Page Seperator and Background Colour

Stereo 3D capture in Decapod requires a solid coloured background, and an object to serve as a page seperator.

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The page seperator is placed in the centre spine (or "gutter") of the book while it is photographed. The page seperator can be a string, a drinking straw, or a pipe cleaner, and must be a solid colour different than the background colour and the colours in the book. Bright red is a good colour if the background is blue or green.
An open book on a green background. Down the middle gutter / spine of the open book is a red string which acts as a page seperator.A solid background and a page seperator is required during stereo 3D capture.

Running Stereo Capture

Filename convention (Untethered capture only)