Stereo 3D calibration is the process of calculating the position and orientation of two cameras relative to each other.
Calibration is important if images are captured using stereo 3D and need to be dewarped - without the calibration information, the stereo images will not flatten.
It is recommended that before any work using stereo 3D is done, this calibration process be completed first.
Calibration uses the same setup as stereo 3D capture. Refer to the Decapod Stereo 3D Guide.
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.
To ensure that this is done properly, follow the these steps:
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.
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.
Download Decapod 10x7 checkerboard
A minimum of 23 pairs of photos are required to perform calibration. More calibration images may yield better results.
Once the set of calibration photo pairs are ready (at least 23 pairs), they are processed through the Decapod Stereo 3D Calibration tool. The Stereo 3D Calibration tool generates a file containing the calibration information, which is then saved to a user-specified location.
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.
Stereo 3D Calibration expects at least 23 image pairs that follow this filename format:
capture-[capture #]-[camera #].[extension]
In this example, images are grouped in pairs. In each pair there is a left and right image as indicated by "-1" and "-2" respectively.
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.
Unlike untethered capture, tethered capture can make the calibration process easier by:
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.
If camera positions are changed, then the new positions need to be recorded by re-calibrating the cameras (retaking the 23 photos and re-running the Decapod Stereo 3D Calibration tool). Once the new calibration data is generated, any subsequent photos taken with these new camera positions should only be used with this new calibration data.
Mixing and matching different stereo image sets and different calibration data is strongly discouraged.
Once all checkerboard calibration images are taken, calibration data needs to be generated by running the Decapod Stereo 3D Calibration tool.
<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.
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.
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.
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.