Table of Contents
Stereo 3D calibration is the process of calculating the position and orientation of two cameras relative to each other.
It is recommended that before any work using stereo 3D is done, this calibration process be completed first.
This documentation applies to Decapod 0.7.
Setting Up Cameras for Calibration
Calibration uses the same setup as stereo 3D capture. Refer to the Decapod Stereo 3D Equipment Guide for the equipment setup, and Decapod Stereo 3D Capture Guide on how to use Decapod's capture tool to take stereo images.
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.
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.
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:
- 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.
- Take test captures to ensure proper positioning. These test captures should be deleted and not be included in the final set calibration images.
- 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.
- Change the tilt / position / orientation of the checkerboard while ensuring it is viewable by both cameras.
- Repeat Steps 3 to 4 until at least 23 pairs of photos are taken.
- 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 with Untethered Cameras
Calibration for untethered cameras is similar to tethered except that the image files from the left and right camera need to be renamed and combined to make a proper matched pair set of pictures.
Stereo 3D Calibration application expects at least 23 image pairs that follow this filename format:
Left camera: capture-[capture #]-0.[camerafile #].[extension]
- capture-01-1.jpg (i.e. left image of capture #1)
- capture-01-2.jpg (i.e. right image of capture #2)
- capture-23-1.jpg (i.e. left image of capture #23)
- capture-23-2.jpg (i.e. right image of capture #23)
Right camera: capture-[capture #]-1.[file extension]
In this example, files from left and right cameras are renamed to create matched pairs. Files with "-0" are for the left images, and "-1" are for the right images.
The left image should always come before the right image in a pair (like in the above example). Reversing this order will cause calibration to give inaccurate results.
- 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.
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.
- Ensure proper filenames of left and right calibration images (see above).
- Create a ZIP file containing all calibration image pairs (at least 23 pairs / 46 images).
- Launch Firefox and load the Stereo 3D Calibration tool by entering the server’s address in the location bar. By default the address is: http://localhost:8080/Image Removed . If the Decapod server can not be loaded at the default address, or if the server is not running, please see your Decapod administrator for assistance.
- Add the ZIP file containing the calibration image pairs (created in Step 2 above) and select “Calibrate” to begin the calibration process.
- Calibration may take 2 hours to complete with high resolution images.
- When calibration is complete, save the file calibration.zip to a location when prompted.
<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.
When the Decapod Capture interface loads, the attached cameras are checked to ensure they will function properly (you may hear the cameras take pictures at this time). If the cameras are matching and supported by the system, then you will receive a message stating that capture is ready and that stereo 3D capture is available.
Before capturing in stereo, it is recommended that Stereo 3D Calibration be run. Without the calibration information, dewarping the stereo 3D images will not be possible.
When all capturing is complete, the stereo images can be saved by selecting the “Download Captures” button. After a short delay, there will be a prompt to download and save the archive containing all the captured images.
To dewarp stereo images, the camera positions used for Stereo Capture need to be recorded and its calibration information generated. To do this, it is recommended that Decapod’s Stereo 3D Calibration tool be run before doing stereo capture work.
For more information about stereo 3D calibration, see the Help documentation in the Decapod Stereo 3D Calibration tool, or the Decapod wiki.
Page Seperator and Background Colour
Stereo 3D capture in Decapod requires a solid coloured background, and an object to serve as a page seperator.
The background is recommended to be a bright green or bright blue, similar to the characteristics of ChromaKey blue and ChromaKey green. ChomaKey blue has an RGB value (0 0 256), and ChromaKey green has RGB value (0 256 0). When positioning the book on the background, it is recommended that some background is visible by both cameras.
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